mirror of https://github.com/explosion/spaCy.git
1483 lines
59 KiB
Markdown
1483 lines
59 KiB
Markdown
---
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title: Linguistic Features
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next: /usage/rule-based-matching
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menu:
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- ['POS Tagging', 'pos-tagging']
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- ['Dependency Parse', 'dependency-parse']
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- ['Named Entities', 'named-entities']
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- ['Entity Linking', 'entity-linking']
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- ['Tokenization', 'tokenization']
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- ['Merging & Splitting', 'retokenization']
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- ['Sentence Segmentation', 'sbd']
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---
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Processing raw text intelligently is difficult: most words are rare, and it's
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common for words that look completely different to mean almost the same thing.
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The same words in a different order can mean something completely different.
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Even splitting text into useful word-like units can be difficult in many
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languages. While it's possible to solve some problems starting from only the raw
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characters, it's usually better to use linguistic knowledge to add useful
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information. That's exactly what spaCy is designed to do: you put in raw text,
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and get back a [`Doc`](/api/doc) object, that comes with a variety of
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annotations.
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## Part-of-speech tagging {#pos-tagging model="tagger, parser"}
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import PosDeps101 from 'usage/101/\_pos-deps.md'
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<PosDeps101 />
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<Infobox title="📖 Part-of-speech tag scheme">
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For a list of the fine-grained and coarse-grained part-of-speech tags assigned
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by spaCy's models across different languages, see the
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[POS tag scheme documentation](/api/annotation#pos-tagging).
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</Infobox>
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### Rule-based morphology {#rule-based-morphology}
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Inflectional morphology is the process by which a root form of a word is
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modified by adding prefixes or suffixes that specify its grammatical function
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but do not changes its part-of-speech. We say that a **lemma** (root form) is
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**inflected** (modified/combined) with one or more **morphological features** to
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create a surface form. Here are some examples:
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| Context | Surface | Lemma | POS | Morphological Features |
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| ---------------------------------------- | ------- | ----- | ---- | ---------------------------------------- |
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| I was reading the paper | reading | read | verb | `VerbForm=Ger` |
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| I don't watch the news, I read the paper | read | read | verb | `VerbForm=Fin`, `Mood=Ind`, `Tense=Pres` |
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| I read the paper yesterday | read | read | verb | `VerbForm=Fin`, `Mood=Ind`, `Tense=Past` |
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English has a relatively simple morphological system, which spaCy handles using
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rules that can be keyed by the token, the part-of-speech tag, or the combination
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of the two. The system works as follows:
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1. The tokenizer consults a
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[mapping table](/usage/adding-languages#tokenizer-exceptions)
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`TOKENIZER_EXCEPTIONS`, which allows sequences of characters to be mapped to
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multiple tokens. Each token may be assigned a part of speech and one or more
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morphological features.
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2. The part-of-speech tagger then assigns each token an **extended POS tag**. In
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the API, these tags are known as `Token.tag`. They express the part-of-speech
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(e.g. `VERB`) and some amount of morphological information, e.g. that the
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verb is past tense.
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3. For words whose POS is not set by a prior process, a
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[mapping table](/usage/adding-languages#tag-map) `TAG_MAP` maps the tags to a
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part-of-speech and a set of morphological features.
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4. Finally, a **rule-based deterministic lemmatizer** maps the surface form, to
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a lemma in light of the previously assigned extended part-of-speech and
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morphological information, without consulting the context of the token. The
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lemmatizer also accepts list-based exception files, acquired from
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[WordNet](https://wordnet.princeton.edu/).
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## Dependency Parsing {#dependency-parse model="parser"}
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spaCy features a fast and accurate syntactic dependency parser, and has a rich
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API for navigating the tree. The parser also powers the sentence boundary
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detection, and lets you iterate over base noun phrases, or "chunks". You can
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check whether a [`Doc`](/api/doc) object has been parsed with the
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`doc.is_parsed` attribute, which returns a boolean value. If this attribute is
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`False`, the default sentence iterator will raise an exception.
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### Noun chunks {#noun-chunks}
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Noun chunks are "base noun phrases" – flat phrases that have a noun as their
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head. You can think of noun chunks as a noun plus the words describing the noun
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– for example, "the lavish green grass" or "the world’s largest tech fund". To
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get the noun chunks in a document, simply iterate over
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[`Doc.noun_chunks`](/api/doc#noun_chunks)
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Autonomous cars shift insurance liability toward manufacturers")
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for chunk in doc.noun_chunks:
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print(chunk.text, chunk.root.text, chunk.root.dep_,
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chunk.root.head.text)
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```
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> - **Text:** The original noun chunk text.
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> - **Root text:** The original text of the word connecting the noun chunk to
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> the rest of the parse.
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> - **Root dep:** Dependency relation connecting the root to its head.
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> - **Root head text:** The text of the root token's head.
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| Text | root.text | root.dep\_ | root.head.text |
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| ------------------- | ------------- | ---------- | -------------- |
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| Autonomous cars | cars | `nsubj` | shift |
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| insurance liability | liability | `dobj` | shift |
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| manufacturers | manufacturers | `pobj` | toward |
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### Navigating the parse tree {#navigating}
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spaCy uses the terms **head** and **child** to describe the words **connected by
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a single arc** in the dependency tree. The term **dep** is used for the arc
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label, which describes the type of syntactic relation that connects the child to
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the head. As with other attributes, the value of `.dep` is a hash value. You can
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get the string value with `.dep_`.
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Autonomous cars shift insurance liability toward manufacturers")
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for token in doc:
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print(token.text, token.dep_, token.head.text, token.head.pos_,
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[child for child in token.children])
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```
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> - **Text:** The original token text.
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> - **Dep:** The syntactic relation connecting child to head.
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> - **Head text:** The original text of the token head.
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> - **Head POS:** The part-of-speech tag of the token head.
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> - **Children:** The immediate syntactic dependents of the token.
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| Text | Dep | Head text | Head POS | Children |
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| ------------- | ---------- | --------- | -------- | ----------------------- |
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| Autonomous | `amod` | cars | `NOUN` | |
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| cars | `nsubj` | shift | `VERB` | Autonomous |
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| shift | `ROOT` | shift | `VERB` | cars, liability, toward |
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| insurance | `compound` | liability | `NOUN` | |
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| liability | `dobj` | shift | `VERB` | insurance |
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| toward | `prep` | shift | `NOUN` | manufacturers |
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| manufacturers | `pobj` | toward | `ADP` | |
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import DisplaCyLong2Html from 'images/displacy-long2.html'
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<Iframe title="displaCy visualization of dependencies and entities 2" html={DisplaCyLong2Html} height={450} />
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Because the syntactic relations form a tree, every word has **exactly one
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head**. You can therefore iterate over the arcs in the tree by iterating over
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the words in the sentence. This is usually the best way to match an arc of
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interest — from below:
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```python
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### {executable="true"}
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import spacy
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from spacy.symbols import nsubj, VERB
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Autonomous cars shift insurance liability toward manufacturers")
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# Finding a verb with a subject from below — good
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verbs = set()
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for possible_subject in doc:
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if possible_subject.dep == nsubj and possible_subject.head.pos == VERB:
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verbs.add(possible_subject.head)
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print(verbs)
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```
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If you try to match from above, you'll have to iterate twice. Once for the head,
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and then again through the children:
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```python
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# Finding a verb with a subject from above — less good
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verbs = []
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for possible_verb in doc:
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if possible_verb.pos == VERB:
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for possible_subject in possible_verb.children:
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if possible_subject.dep == nsubj:
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verbs.append(possible_verb)
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break
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```
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To iterate through the children, use the `token.children` attribute, which
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provides a sequence of [`Token`](/api/token) objects.
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#### Iterating around the local tree {#navigating-around}
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A few more convenience attributes are provided for iterating around the local
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tree from the token. [`Token.lefts`](/api/token#lefts) and
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[`Token.rights`](/api/token#rights) attributes provide sequences of syntactic
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children that occur before and after the token. Both sequences are in sentence
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order. There are also two integer-typed attributes,
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[`Token.n_lefts`](/api/token#n_lefts) and
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[`Token.n_rights`](/api/token#n_rights) that give the number of left and right
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children.
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("bright red apples on the tree")
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print([token.text for token in doc[2].lefts]) # ['bright', 'red']
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print([token.text for token in doc[2].rights]) # ['on']
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print(doc[2].n_lefts) # 2
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print(doc[2].n_rights) # 1
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```
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("de_core_news_sm")
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doc = nlp("schöne rote Äpfel auf dem Baum")
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print([token.text for token in doc[2].lefts]) # ['schöne', 'rote']
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print([token.text for token in doc[2].rights]) # ['auf']
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```
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You can get a whole phrase by its syntactic head using the
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[`Token.subtree`](/api/token#subtree) attribute. This returns an ordered
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sequence of tokens. You can walk up the tree with the
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[`Token.ancestors`](/api/token#ancestors) attribute, and check dominance with
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[`Token.is_ancestor`](/api/token#is_ancestor)
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> #### Projective vs. non-projective
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>
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> For the [default English model](/models/en), the parse tree is **projective**,
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> which means that there are no crossing brackets. The tokens returned by
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> `.subtree` are therefore guaranteed to be contiguous. This is not true for the
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> German model, which has many
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> [non-projective dependencies](https://explosion.ai/blog/german-model#word-order).
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Credit and mortgage account holders must submit their requests")
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root = [token for token in doc if token.head == token][0]
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subject = list(root.lefts)[0]
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for descendant in subject.subtree:
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assert subject is descendant or subject.is_ancestor(descendant)
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print(descendant.text, descendant.dep_, descendant.n_lefts,
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descendant.n_rights,
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[ancestor.text for ancestor in descendant.ancestors])
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```
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| Text | Dep | n_lefts | n_rights | ancestors |
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| -------- | ---------- | ------- | -------- | -------------------------------- |
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| Credit | `nmod` | `0` | `2` | holders, submit |
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| and | `cc` | `0` | `0` | holders, submit |
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| mortgage | `compound` | `0` | `0` | account, Credit, holders, submit |
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| account | `conj` | `1` | `0` | Credit, holders, submit |
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| holders | `nsubj` | `1` | `0` | submit |
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Finally, the `.left_edge` and `.right_edge` attributes can be especially useful,
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because they give you the first and last token of the subtree. This is the
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easiest way to create a `Span` object for a syntactic phrase. Note that
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`.right_edge` gives a token **within** the subtree — so if you use it as the
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end-point of a range, don't forget to `+1`!
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Credit and mortgage account holders must submit their requests")
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span = doc[doc[4].left_edge.i : doc[4].right_edge.i+1]
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with doc.retokenize() as retokenizer:
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retokenizer.merge(span)
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for token in doc:
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print(token.text, token.pos_, token.dep_, token.head.text)
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```
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| Text | POS | Dep | Head text |
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| ----------------------------------- | ------ | ------- | --------- |
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| Credit and mortgage account holders | `NOUN` | `nsubj` | submit |
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| must | `VERB` | `aux` | submit |
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| submit | `VERB` | `ROOT` | submit |
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| their | `ADJ` | `poss` | requests |
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| requests | `NOUN` | `dobj` | submit |
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<Infobox title="📖 Dependency label scheme">
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For a list of the syntactic dependency labels assigned by spaCy's models across
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different languages, see the
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[dependency label scheme documentation](/api/annotation#dependency-parsing).
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</Infobox>
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### Visualizing dependencies {#displacy}
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The best way to understand spaCy's dependency parser is interactively. To make
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this easier, spaCy v2.0+ comes with a visualization module. You can pass a `Doc`
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or a list of `Doc` objects to displaCy and run
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[`displacy.serve`](/api/top-level#displacy.serve) to run the web server, or
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[`displacy.render`](/api/top-level#displacy.render) to generate the raw markup.
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If you want to know how to write rules that hook into some type of syntactic
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construction, just plug the sentence into the visualizer and see how spaCy
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annotates it.
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```python
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### {executable="true"}
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import spacy
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from spacy import displacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("Autonomous cars shift insurance liability toward manufacturers")
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# Since this is an interactive Jupyter environment, we can use displacy.render here
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displacy.render(doc, style='dep')
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```
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<Infobox>
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For more details and examples, see the
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[usage guide on visualizing spaCy](/usage/visualizers). You can also test
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displaCy in our [online demo](https://explosion.ai/demos/displacy)..
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</Infobox>
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### Disabling the parser {#disabling}
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In the [default models](/models), the parser is loaded and enabled as part of
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the [standard processing pipeline](/usage/processing-pipelines). If you don't need
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any of the syntactic information, you should disable the parser. Disabling the
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parser will make spaCy load and run much faster. If you want to load the parser,
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but need to disable it for specific documents, you can also control its use on
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the `nlp` object.
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```python
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nlp = spacy.load("en_core_web_sm", disable=["parser"])
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nlp = English().from_disk("/model", disable=["parser"])
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doc = nlp("I don't want parsed", disable=["parser"])
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```
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<Infobox title="Important note: disabling pipeline components" variant="warning">
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Since spaCy v2.0 comes with better support for customizing the processing
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pipeline components, the `parser` keyword argument has been replaced with
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`disable`, which takes a list of
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[pipeline component names](/usage/processing-pipelines). This lets you disable
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both default and custom components when loading a model, or initializing a
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Language class via [`from_disk`](/api/language#from_disk).
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```diff
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+ nlp = spacy.load("en_core_web_sm", disable=["parser"])
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+ doc = nlp("I don't want parsed", disable=["parser"])
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- nlp = spacy.load("en_core_web_sm", parser=False)
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- doc = nlp("I don't want parsed", parse=False)
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```
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</Infobox>
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## Named Entity Recognition {#named-entities}
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spaCy features an extremely fast statistical entity recognition system, that
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assigns labels to contiguous spans of tokens. The default model identifies a
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variety of named and numeric entities, including companies, locations,
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organizations and products. You can add arbitrary classes to the entity
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recognition system, and update the model with new examples.
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### Named Entity Recognition 101 {#named-entities-101}
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import NER101 from 'usage/101/\_named-entities.md'
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<NER101 />
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### Accessing entity annotations {#accessing}
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The standard way to access entity annotations is the [`doc.ents`](/api/doc#ents)
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property, which produces a sequence of [`Span`](/api/span) objects. The entity
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type is accessible either as a hash value or as a string, using the attributes
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`ent.label` and `ent.label_`. The `Span` object acts as a sequence of tokens, so
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you can iterate over the entity or index into it. You can also get the text form
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of the whole entity, as though it were a single token.
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You can also access token entity annotations using the
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[`token.ent_iob`](/api/token#attributes) and
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[`token.ent_type`](/api/token#attributes) attributes. `token.ent_iob` indicates
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whether an entity starts, continues or ends on the tag. If no entity type is set
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on a token, it will return an empty string.
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> #### IOB Scheme
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>
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> - `I` – Token is inside an entity.
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> - `O` – Token is outside an entity.
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> - `B` – Token is the beginning of an entity.
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|
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```python
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### {executable="true"}
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import spacy
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("San Francisco considers banning sidewalk delivery robots")
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# document level
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ents = [(e.text, e.start_char, e.end_char, e.label_) for e in doc.ents]
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print(ents)
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# token level
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ent_san = [doc[0].text, doc[0].ent_iob_, doc[0].ent_type_]
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ent_francisco = [doc[1].text, doc[1].ent_iob_, doc[1].ent_type_]
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print(ent_san) # ['San', 'B', 'GPE']
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print(ent_francisco) # ['Francisco', 'I', 'GPE']
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```
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| Text | ent_iob | ent_iob\_ | ent_type\_ | Description |
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| --------- | ------- | --------- | ---------- | ---------------------- |
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| San | `3` | `B` | `"GPE"` | beginning of an entity |
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| Francisco | `1` | `I` | `"GPE"` | inside an entity |
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| considers | `2` | `O` | `""` | outside an entity |
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| banning | `2` | `O` | `""` | outside an entity |
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| sidewalk | `2` | `O` | `""` | outside an entity |
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| delivery | `2` | `O` | `""` | outside an entity |
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| robots | `2` | `O` | `""` | outside an entity |
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### Setting entity annotations {#setting-entities}
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To ensure that the sequence of token annotations remains consistent, you have to
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set entity annotations **at the document level**. However, you can't write
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directly to the `token.ent_iob` or `token.ent_type` attributes, so the easiest
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way to set entities is to assign to the [`doc.ents`](/api/doc#ents) attribute
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and create the new entity as a [`Span`](/api/span).
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|
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```python
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### {executable="true"}
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import spacy
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from spacy.tokens import Span
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nlp = spacy.load("en_core_web_sm")
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doc = nlp("fb is hiring a new vice president of global policy")
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ents = [(e.text, e.start_char, e.end_char, e.label_) for e in doc.ents]
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print('Before', ents)
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# the model didn't recognise "fb" as an entity :(
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|
||
fb_ent = Span(doc, 0, 1, label="ORG") # create a Span for the new entity
|
||
doc.ents = list(doc.ents) + [fb_ent]
|
||
|
||
ents = [(e.text, e.start_char, e.end_char, e.label_) for e in doc.ents]
|
||
print('After', ents)
|
||
# [('fb', 0, 2, 'ORG')] 🎉
|
||
```
|
||
|
||
Keep in mind that you need to create a `Span` with the start and end index of
|
||
the **token**, not the start and end index of the entity in the document. In
|
||
this case, "fb" is token `(0, 1)` – but at the document level, the entity will
|
||
have the start and end indices `(0, 2)`.
|
||
|
||
#### Setting entity annotations from array {#setting-from-array}
|
||
|
||
You can also assign entity annotations using the
|
||
[`doc.from_array`](/api/doc#from_array) method. To do this, you should include
|
||
both the `ENT_TYPE` and the `ENT_IOB` attributes in the array you're importing
|
||
from.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import numpy
|
||
import spacy
|
||
from spacy.attrs import ENT_IOB, ENT_TYPE
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp.make_doc("London is a big city in the United Kingdom.")
|
||
print("Before", doc.ents) # []
|
||
|
||
header = [ENT_IOB, ENT_TYPE]
|
||
attr_array = numpy.zeros((len(doc), len(header)), dtype="uint64")
|
||
attr_array[0, 0] = 3 # B
|
||
attr_array[0, 1] = doc.vocab.strings["GPE"]
|
||
doc.from_array(header, attr_array)
|
||
print("After", doc.ents) # [London]
|
||
```
|
||
|
||
#### Setting entity annotations in Cython {#setting-cython}
|
||
|
||
Finally, you can always write to the underlying struct, if you compile a
|
||
[Cython](http://cython.org/) function. This is easy to do, and allows you to
|
||
write efficient native code.
|
||
|
||
```python
|
||
# cython: infer_types=True
|
||
from spacy.tokens.doc cimport Doc
|
||
|
||
cpdef set_entity(Doc doc, int start, int end, int ent_type):
|
||
for i in range(start, end):
|
||
doc.c[i].ent_type = ent_type
|
||
doc.c[start].ent_iob = 3
|
||
for i in range(start+1, end):
|
||
doc.c[i].ent_iob = 2
|
||
```
|
||
|
||
Obviously, if you write directly to the array of `TokenC*` structs, you'll have
|
||
responsibility for ensuring that the data is left in a consistent state.
|
||
|
||
### Built-in entity types {#entity-types}
|
||
|
||
> #### Tip: Understanding entity types
|
||
>
|
||
> You can also use `spacy.explain()` to get the description for the string
|
||
> representation of an entity label. For example, `spacy.explain("LANGUAGE")`
|
||
> will return "any named language".
|
||
|
||
<Infobox title="Annotation scheme">
|
||
|
||
For details on the entity types available in spaCy's pretrained models, see the
|
||
[NER annotation scheme](/api/annotation#named-entities).
|
||
|
||
</Infobox>
|
||
|
||
### Training and updating {#updating}
|
||
|
||
To provide training examples to the entity recognizer, you'll first need to
|
||
create an instance of the [`GoldParse`](/api/goldparse) class. You can specify
|
||
your annotations in a stand-off format or as token tags. If a character offset
|
||
in your entity annotations doesn't fall on a token boundary, the `GoldParse`
|
||
class will treat that annotation as a missing value. This allows for more
|
||
realistic training, because the entity recognizer is allowed to learn from
|
||
examples that may feature tokenizer errors.
|
||
|
||
```python
|
||
train_data = [
|
||
("Who is Chaka Khan?", [(7, 17, "PERSON")]),
|
||
("I like London and Berlin.", [(7, 13, "LOC"), (18, 24, "LOC")]),
|
||
]
|
||
```
|
||
|
||
```python
|
||
doc = Doc(nlp.vocab, ["rats", "make", "good", "pets"])
|
||
gold = GoldParse(doc, entities=["U-ANIMAL", "O", "O", "O"])
|
||
```
|
||
|
||
<Infobox>
|
||
|
||
For more details on **training and updating** the named entity recognizer, see
|
||
the usage guides on [training](/usage/training) or check out the runnable
|
||
[training script](https://github.com/explosion/spaCy/tree/master/examples/training/train_ner.py)
|
||
on GitHub.
|
||
|
||
</Infobox>
|
||
|
||
### Visualizing named entities {#displacy}
|
||
|
||
The
|
||
[displaCy <sup>ENT</sup> visualizer](https://explosion.ai/demos/displacy-ent)
|
||
lets you explore an entity recognition model's behavior interactively. If you're
|
||
training a model, it's very useful to run the visualization yourself. To help
|
||
you do that, spaCy v2.0+ comes with a visualization module. You can pass a `Doc`
|
||
or a list of `Doc` objects to displaCy and run
|
||
[`displacy.serve`](/api/top-level#displacy.serve) to run the web server, or
|
||
[`displacy.render`](/api/top-level#displacy.render) to generate the raw markup.
|
||
|
||
For more details and examples, see the
|
||
[usage guide on visualizing spaCy](/usage/visualizers).
|
||
|
||
```python
|
||
### Named Entity example
|
||
import spacy
|
||
from spacy import displacy
|
||
|
||
text = "When Sebastian Thrun started working on self-driving cars at Google in 2007, few people outside of the company took him seriously."
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp(text)
|
||
displacy.serve(doc, style="ent")
|
||
```
|
||
|
||
import DisplacyEntHtml from 'images/displacy-ent2.html'
|
||
|
||
<Iframe title="displaCy visualizer for entities" html={DisplacyEntHtml} height={180} />
|
||
|
||
## Entity Linking {#entity-linking}
|
||
|
||
To ground the named entities into the "real world", spaCy provides functionality
|
||
to perform entity linking, which resolves a textual entity to a unique
|
||
identifier from a knowledge base (KB). You can create your own
|
||
[`KnowledgeBase`](/api/kb) and
|
||
[train a new Entity Linking model](/usage/training#entity-linker) using that
|
||
custom-made KB.
|
||
|
||
### Accessing entity identifiers {#entity-linking-accessing}
|
||
|
||
The annotated KB identifier is accessible as either a hash value or as a string,
|
||
using the attributes `ent.kb_id` and `ent.kb_id_` of a [`Span`](/api/span)
|
||
object, or the `ent_kb_id` and `ent_kb_id_` attributes of a
|
||
[`Token`](/api/token) object.
|
||
|
||
```python
|
||
import spacy
|
||
|
||
nlp = spacy.load("my_custom_el_model")
|
||
doc = nlp("Ada Lovelace was born in London")
|
||
|
||
# document level
|
||
ents = [(e.text, e.label_, e.kb_id_) for e in doc.ents]
|
||
print(ents) # [('Ada Lovelace', 'PERSON', 'Q7259'), ('London', 'GPE', 'Q84')]
|
||
|
||
# token level
|
||
ent_ada_0 = [doc[0].text, doc[0].ent_type_, doc[0].ent_kb_id_]
|
||
ent_ada_1 = [doc[1].text, doc[1].ent_type_, doc[1].ent_kb_id_]
|
||
ent_london_5 = [doc[5].text, doc[5].ent_type_, doc[5].ent_kb_id_]
|
||
print(ent_ada_0) # ['Ada', 'PERSON', 'Q7259']
|
||
print(ent_ada_1) # ['Lovelace', 'PERSON', 'Q7259']
|
||
print(ent_london_5) # ['London', 'GPE', 'Q84']
|
||
```
|
||
|
||
| Text | ent_type\_ | ent_kb_id\_ |
|
||
| -------- | ---------- | ----------- |
|
||
| Ada | `"PERSON"` | `"Q7259"` |
|
||
| Lovelace | `"PERSON"` | `"Q7259"` |
|
||
| was | - | - |
|
||
| born | - | - |
|
||
| in | - | - |
|
||
| London | `"GPE"` | `"Q84"` |
|
||
|
||
## Tokenization {#tokenization}
|
||
|
||
Tokenization is the task of splitting a text into meaningful segments, called
|
||
_tokens_. The input to the tokenizer is a unicode text, and the output is a
|
||
[`Doc`](/api/doc) object. To construct a `Doc` object, you need a
|
||
[`Vocab`](/api/vocab) instance, a sequence of `word` strings, and optionally a
|
||
sequence of `spaces` booleans, which allow you to maintain alignment of the
|
||
tokens into the original string.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
spaCy's tokenization is **non-destructive**, which means that you'll always be
|
||
able to reconstruct the original input from the tokenized output. Whitespace
|
||
information is preserved in the tokens and no information is added or removed
|
||
during tokenization. This is kind of a core principle of spaCy's `Doc` object:
|
||
`doc.text == input_text` should always hold true.
|
||
|
||
</Infobox>
|
||
|
||
import Tokenization101 from 'usage/101/\_tokenization.md'
|
||
|
||
<Tokenization101 />
|
||
|
||
### Tokenizer data {#101-data}
|
||
|
||
**Global** and **language-specific** tokenizer data is supplied via the language
|
||
data in
|
||
[`spacy/lang`](https://github.com/explosion/spaCy/tree/master/spacy/lang). The
|
||
tokenizer exceptions define special cases like "don't" in English, which needs
|
||
to be split into two tokens: `{ORTH: "do"}` and `{ORTH: "n't", NORM: "not"}`.
|
||
The prefixes, suffixes and infixes mostly define punctuation rules – for
|
||
example, when to split off periods (at the end of a sentence), and when to leave
|
||
tokens containing periods intact (abbreviations like "U.S.").
|
||
|
||
|
||
|
||
<Infobox title="📖 Language data">
|
||
|
||
For more details on the language-specific data, see the usage guide on
|
||
[adding languages](/usage/adding-languages).
|
||
|
||
</Infobox>
|
||
|
||
<Accordion title="Should I change the language data or add custom tokenizer rules?" id="lang-data-vs-tokenizer">
|
||
|
||
Tokenization rules that are specific to one language, but can be **generalized
|
||
across that language** should ideally live in the language data in
|
||
[`spacy/lang`](https://github.com/explosion/spaCy/tree/master/spacy/lang) – we
|
||
always appreciate pull requests! Anything that's specific to a domain or text
|
||
type – like financial trading abbreviations, or Bavarian youth slang – should be
|
||
added as a special case rule to your tokenizer instance. If you're dealing with
|
||
a lot of customizations, it might make sense to create an entirely custom
|
||
subclass.
|
||
|
||
</Accordion>
|
||
|
||
---
|
||
|
||
### Adding special case tokenization rules {#special-cases}
|
||
|
||
Most domains have at least some idiosyncrasies that require custom tokenization
|
||
rules. This could be very certain expressions, or abbreviations only used in
|
||
this specific field. Here's how to add a special case rule to an existing
|
||
[`Tokenizer`](/api/tokenizer) instance:
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.symbols import ORTH
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("gimme that") # phrase to tokenize
|
||
print([w.text for w in doc]) # ['gimme', 'that']
|
||
|
||
# Add special case rule
|
||
special_case = [{ORTH: "gim"}, {ORTH: "me"}]
|
||
nlp.tokenizer.add_special_case("gimme", special_case)
|
||
|
||
# Check new tokenization
|
||
print([w.text for w in nlp("gimme that")]) # ['gim', 'me', 'that']
|
||
```
|
||
|
||
The special case doesn't have to match an entire whitespace-delimited substring.
|
||
The tokenizer will incrementally split off punctuation, and keep looking up the
|
||
remaining substring:
|
||
|
||
```python
|
||
assert "gimme" not in [w.text for w in nlp("gimme!")]
|
||
assert "gimme" not in [w.text for w in nlp('("...gimme...?")')]
|
||
```
|
||
|
||
The special case rules have precedence over the punctuation splitting:
|
||
|
||
```python
|
||
nlp.tokenizer.add_special_case("...gimme...?", [{"ORTH": "...gimme...?"}])
|
||
assert len(nlp("...gimme...?")) == 1
|
||
```
|
||
|
||
### How spaCy's tokenizer works {#how-tokenizer-works}
|
||
|
||
spaCy introduces a novel tokenization algorithm, that gives a better balance
|
||
between performance, ease of definition, and ease of alignment into the original
|
||
string.
|
||
|
||
After consuming a prefix or suffix, we consult the special cases again. We want
|
||
the special cases to handle things like "don't" in English, and we want the same
|
||
rule to work for "(don't)!". We do this by splitting off the open bracket, then
|
||
the exclamation, then the close bracket, and finally matching the special case.
|
||
Here's an implementation of the algorithm in Python, optimized for readability
|
||
rather than performance:
|
||
|
||
```python
|
||
def tokenizer_pseudo_code(self, special_cases, prefix_search, suffix_search,
|
||
infix_finditer, token_match, url_match):
|
||
tokens = []
|
||
for substring in text.split():
|
||
suffixes = []
|
||
while substring:
|
||
while prefix_search(substring) or suffix_search(substring):
|
||
if token_match(substring):
|
||
tokens.append(substring)
|
||
substring = ''
|
||
break
|
||
if substring in special_cases:
|
||
tokens.extend(special_cases[substring])
|
||
substring = ''
|
||
break
|
||
if prefix_search(substring):
|
||
split = prefix_search(substring).end()
|
||
tokens.append(substring[:split])
|
||
substring = substring[split:]
|
||
if substring in special_cases:
|
||
continue
|
||
if suffix_search(substring):
|
||
split = suffix_search(substring).start()
|
||
suffixes.append(substring[split:])
|
||
substring = substring[:split]
|
||
if token_match(substring):
|
||
tokens.append(substring)
|
||
substring = ''
|
||
elif url_match(substring):
|
||
tokens.append(substring)
|
||
substring = ''
|
||
elif substring in special_cases:
|
||
tokens.extend(special_cases[substring])
|
||
substring = ''
|
||
elif list(infix_finditer(substring)):
|
||
infixes = infix_finditer(substring)
|
||
offset = 0
|
||
for match in infixes:
|
||
tokens.append(substring[offset : match.start()])
|
||
tokens.append(substring[match.start() : match.end()])
|
||
offset = match.end()
|
||
if substring[offset:]:
|
||
tokens.append(substring[offset:])
|
||
substring = ''
|
||
elif substring:
|
||
tokens.append(substring)
|
||
substring = ''
|
||
tokens.extend(reversed(suffixes))
|
||
return tokens
|
||
```
|
||
|
||
The algorithm can be summarized as follows:
|
||
|
||
1. Iterate over whitespace-separated substrings.
|
||
2. Look for a token match. If there is a match, stop processing and keep this
|
||
token.
|
||
3. Check whether we have an explicitly defined special case for this substring.
|
||
If we do, use it.
|
||
4. Otherwise, try to consume one prefix. If we consumed a prefix, go back to
|
||
#2, so that the token match and special cases always get priority.
|
||
5. If we didn't consume a prefix, try to consume a suffix and then go back to
|
||
#2.
|
||
6. If we can't consume a prefix or a suffix, look for a URL match.
|
||
7. If there's no URL match, then look for a special case.
|
||
8. Look for "infixes" — stuff like hyphens etc. and split the substring into
|
||
tokens on all infixes.
|
||
9. Once we can't consume any more of the string, handle it as a single token.
|
||
|
||
#### Debugging the tokenizer {#tokenizer-debug new="2.2.3"}
|
||
|
||
A working implementation of the pseudo-code above is available for debugging as
|
||
[`nlp.tokenizer.explain(text)`](/api/tokenizer#explain). It returns a list of
|
||
tuples showing which tokenizer rule or pattern was matched for each token. The
|
||
tokens produced are identical to `nlp.tokenizer()` except for whitespace tokens:
|
||
|
||
```python
|
||
### {executable="true"}
|
||
from spacy.lang.en import English
|
||
|
||
nlp = English()
|
||
text = '''"Let's go!"'''
|
||
doc = nlp(text)
|
||
tok_exp = nlp.tokenizer.explain(text)
|
||
assert [t.text for t in doc if not t.is_space] == [t[1] for t in tok_exp]
|
||
for t in tok_exp:
|
||
print(t[1], "\\t", t[0])
|
||
|
||
# " PREFIX
|
||
# Let SPECIAL-1
|
||
# 's SPECIAL-2
|
||
# go TOKEN
|
||
# ! SUFFIX
|
||
# " SUFFIX
|
||
```
|
||
|
||
### Customizing spaCy's Tokenizer class {#native-tokenizers}
|
||
|
||
Let's imagine you wanted to create a tokenizer for a new language or specific
|
||
domain. There are six things you may need to define:
|
||
|
||
1. A dictionary of **special cases**. This handles things like contractions,
|
||
units of measurement, emoticons, certain abbreviations, etc.
|
||
2. A function `prefix_search`, to handle **preceding punctuation**, such as open
|
||
quotes, open brackets, etc.
|
||
3. A function `suffix_search`, to handle **succeeding punctuation**, such as
|
||
commas, periods, close quotes, etc.
|
||
4. A function `infixes_finditer`, to handle non-whitespace separators, such as
|
||
hyphens etc.
|
||
5. An optional boolean function `token_match` matching strings that should never
|
||
be split, overriding the infix rules. Useful for things like numbers.
|
||
6. An optional boolean function `url_match`, which is similar to `token_match`
|
||
except that prefixes and suffixes are removed before applying the match.
|
||
|
||
<Infobox title="Important note: token match in spaCy v2.2" variant="warning">
|
||
|
||
In spaCy v2.2.2-v2.2.4, the `token_match` was equivalent to the `url_match`
|
||
above and there was no match pattern applied before prefixes and suffixes were
|
||
analyzed. As of spaCy v2.3.0, the `token_match` has been reverted to its
|
||
behavior in v2.2.1 and earlier with precedence over prefixes and suffixes.
|
||
|
||
The `url_match` is introduced in v2.3.0 to handle cases like URLs where the
|
||
tokenizer should remove prefixes and suffixes (e.g., a comma at the end of a
|
||
URL) before applying the match.
|
||
|
||
</Infobox>
|
||
|
||
You shouldn't usually need to create a `Tokenizer` subclass. Standard usage is
|
||
to use `re.compile()` to build a regular expression object, and pass its
|
||
`.search()` and `.finditer()` methods:
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import re
|
||
import spacy
|
||
from spacy.tokenizer import Tokenizer
|
||
|
||
special_cases = {":)": [{"ORTH": ":)"}]}
|
||
prefix_re = re.compile(r'''^[\[\("']''')
|
||
suffix_re = re.compile(r'''[\]\)"']$''')
|
||
infix_re = re.compile(r'''[-~]''')
|
||
simple_url_re = re.compile(r'''^https?://''')
|
||
|
||
def custom_tokenizer(nlp):
|
||
return Tokenizer(nlp.vocab, rules=special_cases,
|
||
prefix_search=prefix_re.search,
|
||
suffix_search=suffix_re.search,
|
||
infix_finditer=infix_re.finditer,
|
||
url_match=simple_url_re.match)
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
nlp.tokenizer = custom_tokenizer(nlp)
|
||
doc = nlp("hello-world. :)")
|
||
print([t.text for t in doc]) # ['hello', '-', 'world.', ':)']
|
||
```
|
||
|
||
If you need to subclass the tokenizer instead, the relevant methods to
|
||
specialize are `find_prefix`, `find_suffix` and `find_infix`.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
When customizing the prefix, suffix and infix handling, remember that you're
|
||
passing in **functions** for spaCy to execute, e.g. `prefix_re.search` – not
|
||
just the regular expressions. This means that your functions also need to define
|
||
how the rules should be applied. For example, if you're adding your own prefix
|
||
rules, you need to make sure they're only applied to characters at the
|
||
**beginning of a token**, e.g. by adding `^`. Similarly, suffix rules should
|
||
only be applied at the **end of a token**, so your expression should end with a
|
||
`$`.
|
||
|
||
</Infobox>
|
||
|
||
#### Modifying existing rule sets {#native-tokenizer-additions}
|
||
|
||
In many situations, you don't necessarily need entirely custom rules. Sometimes
|
||
you just want to add another character to the prefixes, suffixes or infixes. The
|
||
default prefix, suffix and infix rules are available via the `nlp` object's
|
||
`Defaults` and the `Tokenizer` attributes such as
|
||
[`Tokenizer.suffix_search`](/api/tokenizer#attributes) are writable, so you can
|
||
overwrite them with compiled regular expression objects using modified default
|
||
rules. spaCy ships with utility functions to help you compile the regular
|
||
expressions – for example,
|
||
[`compile_suffix_regex`](/api/top-level#util.compile_suffix_regex):
|
||
|
||
```python
|
||
suffixes = nlp.Defaults.suffixes + (r'''-+$''',)
|
||
suffix_regex = spacy.util.compile_suffix_regex(suffixes)
|
||
nlp.tokenizer.suffix_search = suffix_regex.search
|
||
```
|
||
|
||
Similarly, you can remove a character from the default suffixes:
|
||
|
||
```python
|
||
suffixes = list(nlp.Defaults.suffixes)
|
||
suffixes.remove("\\\\[")
|
||
suffix_regex = spacy.util.compile_suffix_regex(suffixes)
|
||
nlp.tokenizer.suffix_search = suffix_regex.search
|
||
```
|
||
|
||
The `Tokenizer.suffix_search` attribute should be a function which takes a
|
||
unicode string and returns a **regex match object** or `None`. Usually we use
|
||
the `.search` attribute of a compiled regex object, but you can use some other
|
||
function that behaves the same way.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
If you're using a statistical model, writing to the `nlp.Defaults` or
|
||
`English.Defaults` directly won't work, since the regular expressions are read
|
||
from the model and will be compiled when you load it. If you modify
|
||
`nlp.Defaults`, you'll only see the effect if you call
|
||
[`spacy.blank`](/api/top-level#spacy.blank) or `Defaults.create_tokenizer()`. If
|
||
you want to modify the tokenizer loaded from a statistical model, you should
|
||
modify `nlp.tokenizer` directly.
|
||
|
||
</Infobox>
|
||
|
||
The prefix, infix and suffix rule sets include not only individual characters
|
||
but also detailed regular expressions that take the surrounding context into
|
||
account. For example, there is a regular expression that treats a hyphen between
|
||
letters as an infix. If you do not want the tokenizer to split on hyphens
|
||
between letters, you can modify the existing infix definition from
|
||
[`lang/punctuation.py`](https://github.com/explosion/spaCy/blob/master/spacy/lang/punctuation.py):
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.lang.char_classes import ALPHA, ALPHA_LOWER, ALPHA_UPPER
|
||
from spacy.lang.char_classes import CONCAT_QUOTES, LIST_ELLIPSES, LIST_ICONS
|
||
from spacy.util import compile_infix_regex
|
||
|
||
# default tokenizer
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("mother-in-law")
|
||
print([t.text for t in doc]) # ['mother', '-', 'in', '-', 'law']
|
||
|
||
# modify tokenizer infix patterns
|
||
infixes = (
|
||
LIST_ELLIPSES
|
||
+ LIST_ICONS
|
||
+ [
|
||
r"(?<=[0-9])[+\\-\\*^](?=[0-9-])",
|
||
r"(?<=[{al}{q}])\\.(?=[{au}{q}])".format(
|
||
al=ALPHA_LOWER, au=ALPHA_UPPER, q=CONCAT_QUOTES
|
||
),
|
||
r"(?<=[{a}]),(?=[{a}])".format(a=ALPHA),
|
||
# EDIT: commented out regex that splits on hyphens between letters:
|
||
#r"(?<=[{a}])(?:{h})(?=[{a}])".format(a=ALPHA, h=HYPHENS),
|
||
r"(?<=[{a}0-9])[:<>=/](?=[{a}])".format(a=ALPHA),
|
||
]
|
||
)
|
||
|
||
infix_re = compile_infix_regex(infixes)
|
||
nlp.tokenizer.infix_finditer = infix_re.finditer
|
||
doc = nlp("mother-in-law")
|
||
print([t.text for t in doc]) # ['mother-in-law']
|
||
```
|
||
|
||
For an overview of the default regular expressions, see
|
||
[`lang/punctuation.py`](https://github.com/explosion/spaCy/blob/master/spacy/lang/punctuation.py)
|
||
and language-specific definitions such as
|
||
[`lang/de/punctuation.py`](https://github.com/explosion/spaCy/blob/master/spacy/lang/de/punctuation.py)
|
||
for German.
|
||
|
||
### Hooking an arbitrary tokenizer into the pipeline {#custom-tokenizer}
|
||
|
||
The tokenizer is the first component of the processing pipeline and the only one
|
||
that can't be replaced by writing to `nlp.pipeline`. This is because it has a
|
||
different signature from all the other components: it takes a text and returns a
|
||
`Doc`, whereas all other components expect to already receive a tokenized `Doc`.
|
||
|
||
|
||
|
||
To overwrite the existing tokenizer, you need to replace `nlp.tokenizer` with a
|
||
custom function that takes a text, and returns a `Doc`.
|
||
|
||
```python
|
||
nlp = spacy.load("en_core_web_sm")
|
||
nlp.tokenizer = my_tokenizer
|
||
```
|
||
|
||
| Argument | Type | Description |
|
||
| ----------- | ------- | ------------------------- |
|
||
| `text` | unicode | The raw text to tokenize. |
|
||
| **RETURNS** | `Doc` | The tokenized document. |
|
||
|
||
<Infobox title="Important note: using a custom tokenizer" variant="warning">
|
||
|
||
In spaCy v1.x, you had to add a custom tokenizer by passing it to the `make_doc`
|
||
keyword argument, or by passing a tokenizer "factory" to `create_make_doc`. This
|
||
was unnecessarily complicated. Since spaCy v2.0, you can write to
|
||
`nlp.tokenizer` instead. If your tokenizer needs the vocab, you can write a
|
||
function and use `nlp.vocab`.
|
||
|
||
```diff
|
||
- nlp = spacy.load("en_core_web_sm", make_doc=my_tokenizer)
|
||
- nlp = spacy.load("en_core_web_sm", create_make_doc=my_tokenizer_factory)
|
||
|
||
+ nlp.tokenizer = my_tokenizer
|
||
+ nlp.tokenizer = my_tokenizer_factory(nlp.vocab)
|
||
```
|
||
|
||
</Infobox>
|
||
|
||
### Example: A custom whitespace tokenizer {#custom-tokenizer-example}
|
||
|
||
To construct the tokenizer, we usually want attributes of the `nlp` pipeline.
|
||
Specifically, we want the tokenizer to hold a reference to the vocabulary
|
||
object. Let's say we have the following class as our tokenizer:
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.tokens import Doc
|
||
|
||
class WhitespaceTokenizer(object):
|
||
def __init__(self, vocab):
|
||
self.vocab = vocab
|
||
|
||
def __call__(self, text):
|
||
words = text.split(' ')
|
||
# All tokens 'own' a subsequent space character in this tokenizer
|
||
spaces = [True] * len(words)
|
||
return Doc(self.vocab, words=words, spaces=spaces)
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
nlp.tokenizer = WhitespaceTokenizer(nlp.vocab)
|
||
doc = nlp("What's happened to me? he thought. It wasn't a dream.")
|
||
print([t.text for t in doc])
|
||
```
|
||
|
||
As you can see, we need a `Vocab` instance to construct this — but we won't have
|
||
it until we get back the loaded `nlp` object. The simplest solution is to build
|
||
the tokenizer in two steps. This also means that you can reuse the "tokenizer
|
||
factory" and initialize it with different instances of `Vocab`.
|
||
|
||
### Bringing your own annotations {#own-annotations}
|
||
|
||
spaCy generally assumes by default that your data is raw text. However,
|
||
sometimes your data is partially annotated, e.g. with pre-existing tokenization,
|
||
part-of-speech tags, etc. The most common situation is that you have pre-defined
|
||
tokenization. If you have a list of strings, you can create a `Doc` object
|
||
directly. Optionally, you can also specify a list of boolean values, indicating
|
||
whether each word has a subsequent space.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.tokens import Doc
|
||
from spacy.lang.en import English
|
||
|
||
nlp = English()
|
||
doc = Doc(nlp.vocab, words=["Hello", ",", "world", "!"],
|
||
spaces=[False, True, False, False])
|
||
print([(t.text, t.text_with_ws, t.whitespace_) for t in doc])
|
||
```
|
||
|
||
If provided, the spaces list must be the same length as the words list. The
|
||
spaces list affects the `doc.text`, `span.text`, `token.idx`, `span.start_char`
|
||
and `span.end_char` attributes. If you don't provide a `spaces` sequence, spaCy
|
||
will assume that all words are whitespace delimited.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.tokens import Doc
|
||
from spacy.lang.en import English
|
||
|
||
nlp = English()
|
||
bad_spaces = Doc(nlp.vocab, words=["Hello", ",", "world", "!"])
|
||
good_spaces = Doc(nlp.vocab, words=["Hello", ",", "world", "!"],
|
||
spaces=[False, True, False, False])
|
||
|
||
print(bad_spaces.text) # 'Hello , world !'
|
||
print(good_spaces.text) # 'Hello, world!'
|
||
```
|
||
|
||
Once you have a [`Doc`](/api/doc) object, you can write to its attributes to set
|
||
the part-of-speech tags, syntactic dependencies, named entities and other
|
||
attributes. For details, see the respective usage pages.
|
||
|
||
### Aligning tokenization {#aligning-tokenization}
|
||
|
||
spaCy's tokenization is non-destructive and uses language-specific rules
|
||
optimized for compatibility with treebank annotations. Other tools and resources
|
||
can sometimes tokenize things differently – for example, `"I'm"` →
|
||
`["I", "'", "m"]` instead of `["I", "'m"]`.
|
||
|
||
In situations like that, you often want to align the tokenization so that you
|
||
can merge annotations from different sources together, or take vectors predicted
|
||
by a
|
||
[pretrained BERT model](https://github.com/huggingface/pytorch-transformers) and
|
||
apply them to spaCy tokens. spaCy's [`gold.align`](/api/goldparse#align) helper
|
||
returns a `(cost, a2b, b2a, a2b_multi, b2a_multi)` tuple describing the number
|
||
of misaligned tokens, the one-to-one mappings of token indices in both
|
||
directions and the indices where multiple tokens align to one single token.
|
||
|
||
> #### ✏️ Things to try
|
||
>
|
||
> 1. Change the capitalization in one of the token lists – for example,
|
||
> `"obama"` to `"Obama"`. You'll see that the alignment is case-insensitive.
|
||
> 2. Change `"podcasts"` in `other_tokens` to `"pod", "casts"`. You should see
|
||
> that there are now 4 misaligned tokens and that the new many-to-one mapping
|
||
> is reflected in `a2b_multi`.
|
||
> 3. Make `other_tokens` and `spacy_tokens` identical. You'll see that the
|
||
> `cost` is `0` and all corresponding mappings are also identical.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
from spacy.gold import align
|
||
|
||
other_tokens = ["i", "listened", "to", "obama", "'", "s", "podcasts", "."]
|
||
spacy_tokens = ["i", "listened", "to", "obama", "'s", "podcasts", "."]
|
||
cost, a2b, b2a, a2b_multi, b2a_multi = align(other_tokens, spacy_tokens)
|
||
print("Edit distance:", cost) # 3
|
||
print("One-to-one mappings a -> b", a2b) # array([0, 1, 2, 3, -1, -1, 5, 6])
|
||
print("One-to-one mappings b -> a", b2a) # array([0, 1, 2, 3, -1, 6, 7])
|
||
print("Many-to-one mappings a -> b", a2b_multi) # {4: 4, 5: 4}
|
||
print("Many-to-one mappings b-> a", b2a_multi) # {}
|
||
```
|
||
|
||
Here are some insights from the alignment information generated in the example
|
||
above:
|
||
|
||
- The edit distance (cost) is `3`: two deletions and one insertion.
|
||
- The one-to-one mappings for the first four tokens are identical, which means
|
||
they map to each other. This makes sense because they're also identical in the
|
||
input: `"i"`, `"listened"`, `"to"` and `"obama"`.
|
||
- The index mapped to `a2b[6]` is `5`, which means that `other_tokens[6]`
|
||
(`"podcasts"`) aligns to `spacy_tokens[5]` (also `"podcasts"`).
|
||
- `a2b[4]` is `-1`, which means that there is no one-to-one alignment for the
|
||
token at `other_tokens[4]`. The token `"'"` doesn't exist on its own in
|
||
`spacy_tokens`. The same goes for `a2b[5]` and `other_tokens[5]`, i.e. `"s"`.
|
||
- The dictionary `a2b_multi` shows that both tokens 4 and 5 of `other_tokens`
|
||
(`"'"` and `"s"`) align to token 4 of `spacy_tokens` (`"'s"`).
|
||
- The dictionary `b2a_multi` shows that there are no tokens in `spacy_tokens`
|
||
that map to multiple tokens in `other_tokens`.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
The current implementation of the alignment algorithm assumes that both
|
||
tokenizations add up to the same string. For example, you'll be able to align
|
||
`["I", "'", "m"]` and `["I", "'m"]`, which both add up to `"I'm"`, but not
|
||
`["I", "'m"]` and `["I", "am"]`.
|
||
|
||
</Infobox>
|
||
|
||
## Merging and splitting {#retokenization new="2.1"}
|
||
|
||
The [`Doc.retokenize`](/api/doc#retokenize) context manager lets you merge and
|
||
split tokens. Modifications to the tokenization are stored and performed all at
|
||
once when the context manager exits. To merge several tokens into one single
|
||
token, pass a `Span` to [`retokenizer.merge`](/api/doc#retokenizer.merge). An
|
||
optional dictionary of `attrs` lets you set attributes that will be assigned to
|
||
the merged token – for example, the lemma, part-of-speech tag or entity type. By
|
||
default, the merged token will receive the same attributes as the merged span's
|
||
root.
|
||
|
||
> #### ✏️ Things to try
|
||
>
|
||
> 1. Inspect the `token.lemma_` attribute with and without setting the `attrs`.
|
||
> You'll see that the lemma defaults to "New", the lemma of the span's root.
|
||
> 2. Overwrite other attributes like the `"ENT_TYPE"`. Since "New York" is also
|
||
> recognized as a named entity, this change will also be reflected in the
|
||
> `doc.ents`.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("I live in New York")
|
||
print("Before:", [token.text for token in doc])
|
||
|
||
with doc.retokenize() as retokenizer:
|
||
retokenizer.merge(doc[3:5], attrs={"LEMMA": "new york"})
|
||
print("After:", [token.text for token in doc])
|
||
```
|
||
|
||
> #### Tip: merging entities and noun phrases
|
||
>
|
||
> If you need to merge named entities or noun chunks, check out the built-in
|
||
> [`merge_entities`](/api/pipeline-functions#merge_entities) and
|
||
> [`merge_noun_chunks`](/api/pipeline-functions#merge_noun_chunks) pipeline
|
||
> components. When added to your pipeline using `nlp.add_pipe`, they'll take
|
||
> care of merging the spans automatically.
|
||
|
||
If an attribute in the `attrs` is a context-dependent token attribute, it will
|
||
be applied to the underlying [`Token`](/api/token). For example `LEMMA`, `POS`
|
||
or `DEP` only apply to a word in context, so they're token attributes. If an
|
||
attribute is a context-independent lexical attribute, it will be applied to the
|
||
underlying [`Lexeme`](/api/lexeme), the entry in the vocabulary. For example,
|
||
`LOWER` or `IS_STOP` apply to all words of the same spelling, regardless of the
|
||
context.
|
||
|
||
<Infobox variant="warning" title="Note on merging overlapping spans">
|
||
|
||
If you're trying to merge spans that overlap, spaCy will raise an error because
|
||
it's unclear how the result should look. Depending on the application, you may
|
||
want to match the shortest or longest possible span, so it's up to you to filter
|
||
them. If you're looking for the longest non-overlapping span, you can use the
|
||
[`util.filter_spans`](/api/top-level#util.filter_spans) helper:
|
||
|
||
```python
|
||
doc = nlp("I live in Berlin Kreuzberg")
|
||
spans = [doc[3:5], doc[3:4], doc[4:5]]
|
||
filtered_spans = filter_spans(spans)
|
||
```
|
||
|
||
</Infobox>
|
||
|
||
### Splitting tokens
|
||
|
||
The [`retokenizer.split`](/api/doc#retokenizer.split) method allows splitting
|
||
one token into two or more tokens. This can be useful for cases where
|
||
tokenization rules alone aren't sufficient. For example, you might want to split
|
||
"its" into the tokens "it" and "is" — but not the possessive pronoun "its". You
|
||
can write rule-based logic that can find only the correct "its" to split, but by
|
||
that time, the `Doc` will already be tokenized.
|
||
|
||
This process of splitting a token requires more settings, because you need to
|
||
specify the text of the individual tokens, optional per-token attributes and how
|
||
the should be attached to the existing syntax tree. This can be done by
|
||
supplying a list of `heads` – either the token to attach the newly split token
|
||
to, or a `(token, subtoken)` tuple if the newly split token should be attached
|
||
to another subtoken. In this case, "New" should be attached to "York" (the
|
||
second split subtoken) and "York" should be attached to "in".
|
||
|
||
> #### ✏️ Things to try
|
||
>
|
||
> 1. Assign different attributes to the subtokens and compare the result.
|
||
> 2. Change the heads so that "New" is attached to "in" and "York" is attached
|
||
> to "New".
|
||
> 3. Split the token into three tokens instead of two – for example,
|
||
> `["New", "Yo", "rk"]`.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy import displacy
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("I live in NewYork")
|
||
print("Before:", [token.text for token in doc])
|
||
displacy.render(doc) # displacy.serve if you're not in a Jupyter environment
|
||
|
||
with doc.retokenize() as retokenizer:
|
||
heads = [(doc[3], 1), doc[2]]
|
||
attrs = {"POS": ["PROPN", "PROPN"], "DEP": ["pobj", "compound"]}
|
||
retokenizer.split(doc[3], ["New", "York"], heads=heads, attrs=attrs)
|
||
print("After:", [token.text for token in doc])
|
||
displacy.render(doc) # displacy.serve if you're not in a Jupyter environment
|
||
```
|
||
|
||
Specifying the heads as a list of `token` or `(token, subtoken)` tuples allows
|
||
attaching split subtokens to other subtokens, without having to keep track of
|
||
the token indices after splitting.
|
||
|
||
| Token | Head | Description |
|
||
| -------- | ------------- | --------------------------------------------------------------------------------------------------- |
|
||
| `"New"` | `(doc[3], 1)` | Attach this token to the second subtoken (index `1`) that `doc[3]` will be split into, i.e. "York". |
|
||
| `"York"` | `doc[2]` | Attach this token to `doc[1]` in the original `Doc`, i.e. "in". |
|
||
|
||
If you don't care about the heads (for example, if you're only running the
|
||
tokenizer and not the parser), you can each subtoken to itself:
|
||
|
||
```python
|
||
### {highlight="3"}
|
||
doc = nlp("I live in NewYorkCity")
|
||
with doc.retokenize() as retokenizer:
|
||
heads = [(doc[3], 0), (doc[3], 1), (doc[3], 2)]
|
||
retokenizer.split(doc[3], ["New", "York", "City"], heads=heads)
|
||
```
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
When splitting tokens, the subtoken texts always have to match the original
|
||
token text – or, put differently `"".join(subtokens) == token.text` always needs
|
||
to hold true. If this wasn't the case, splitting tokens could easily end up
|
||
producing confusing and unexpected results that would contradict spaCy's
|
||
non-destructive tokenization policy.
|
||
|
||
```diff
|
||
doc = nlp("I live in L.A.")
|
||
with doc.retokenize() as retokenizer:
|
||
- retokenizer.split(doc[3], ["Los", "Angeles"], heads=[(doc[3], 1), doc[2]])
|
||
+ retokenizer.split(doc[3], ["L.", "A."], heads=[(doc[3], 1), doc[2]])
|
||
```
|
||
|
||
</Infobox>
|
||
|
||
### Overwriting custom extension attributes {#retokenization-extensions}
|
||
|
||
If you've registered custom
|
||
[extension attributes](/usage/processing-pipelines#custom-components-attributes),
|
||
you can overwrite them during tokenization by providing a dictionary of
|
||
attribute names mapped to new values as the `"_"` key in the `attrs`. For
|
||
merging, you need to provide one dictionary of attributes for the resulting
|
||
merged token. For splitting, you need to provide a list of dictionaries with
|
||
custom attributes, one per split subtoken.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
To set extension attributes during retokenization, the attributes need to be
|
||
**registered** using the [`Token.set_extension`](/api/token#set_extension)
|
||
method and they need to be **writable**. This means that they should either have
|
||
a default value that can be overwritten, or a getter _and_ setter. Method
|
||
extensions or extensions with only a getter are computed dynamically, so their
|
||
values can't be overwritten. For more details, see the
|
||
[extension attribute docs](/usage/processing-pipelines/#custom-components-attributes).
|
||
|
||
</Infobox>
|
||
|
||
> #### ✏️ Things to try
|
||
>
|
||
> 1. Add another custom extension – maybe `"music_style"`? – and overwrite it.
|
||
> 2. Change the extension attribute to use only a `getter` function. You should
|
||
> see that spaCy raises an error, because the attribute is not writable
|
||
> anymore.
|
||
> 3. Rewrite the code to split a token with `retokenizer.split`. Remember that
|
||
> you need to provide a list of extension attribute values as the `"_"`
|
||
> property, one for each split subtoken.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.tokens import Token
|
||
|
||
# Register a custom token attribute, token._.is_musician
|
||
Token.set_extension("is_musician", default=False)
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("I like David Bowie")
|
||
print("Before:", [(token.text, token._.is_musician) for token in doc])
|
||
|
||
with doc.retokenize() as retokenizer:
|
||
retokenizer.merge(doc[2:4], attrs={"_": {"is_musician": True}})
|
||
print("After:", [(token.text, token._.is_musician) for token in doc])
|
||
```
|
||
|
||
## Sentence Segmentation {#sbd}
|
||
|
||
A [`Doc`](/api/doc) object's sentences are available via the `Doc.sents`
|
||
property. Unlike other libraries, spaCy uses the dependency parse to determine
|
||
sentence boundaries. This is usually more accurate than a rule-based approach,
|
||
but it also means you'll need a **statistical model** and accurate predictions.
|
||
If your texts are closer to general-purpose news or web text, this should work
|
||
well out-of-the-box. For social media or conversational text that doesn't follow
|
||
the same rules, your application may benefit from a custom rule-based
|
||
implementation. You can either use the built-in
|
||
[`Sentencizer`](/api/sentencizer) or plug an entirely custom rule-based function
|
||
into your [processing pipeline](/usage/processing-pipelines).
|
||
|
||
spaCy's dependency parser respects already set boundaries, so you can preprocess
|
||
your `Doc` using custom rules _before_ it's parsed. Depending on your text, this
|
||
may also improve accuracy, since the parser is constrained to predict parses
|
||
consistent with the sentence boundaries.
|
||
|
||
### Default: Using the dependency parse {#sbd-parser model="parser"}
|
||
|
||
To view a `Doc`'s sentences, you can iterate over the `Doc.sents`, a generator
|
||
that yields [`Span`](/api/span) objects.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp("This is a sentence. This is another sentence.")
|
||
for sent in doc.sents:
|
||
print(sent.text)
|
||
```
|
||
|
||
### Rule-based pipeline component {#sbd-component}
|
||
|
||
The [`Sentencizer`](/api/sentencizer) component is a
|
||
[pipeline component](/usage/processing-pipelines) that splits sentences on
|
||
punctuation like `.`, `!` or `?`. You can plug it into your pipeline if you only
|
||
need sentence boundaries without the dependency parse.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
from spacy.lang.en import English
|
||
|
||
nlp = English() # just the language with no model
|
||
sentencizer = nlp.create_pipe("sentencizer")
|
||
nlp.add_pipe(sentencizer)
|
||
doc = nlp("This is a sentence. This is another sentence.")
|
||
for sent in doc.sents:
|
||
print(sent.text)
|
||
```
|
||
|
||
### Custom rule-based strategy {id="sbd-custom"}
|
||
|
||
If you want to implement your own strategy that differs from the default
|
||
rule-based approach of splitting on sentences, you can also create a
|
||
[custom pipeline component](/usage/processing-pipelines#custom-components) that
|
||
takes a `Doc` object and sets the `Token.is_sent_start` attribute on each
|
||
individual token. If set to `False`, the token is explicitly marked as _not_ the
|
||
start of a sentence. If set to `None` (default), it's treated as a missing value
|
||
and can still be overwritten by the parser.
|
||
|
||
<Infobox title="Important note" variant="warning">
|
||
|
||
To prevent inconsistent state, you can only set boundaries **before** a document
|
||
is parsed (and `Doc.is_parsed` is `False`). To ensure that your component is
|
||
added in the right place, you can set `before='parser'` or `first=True` when
|
||
adding it to the pipeline using [`nlp.add_pipe`](/api/language#add_pipe).
|
||
|
||
</Infobox>
|
||
|
||
Here's an example of a component that implements a pre-processing rule for
|
||
splitting on `'...'` tokens. The component is added before the parser, which is
|
||
then used to further segment the text. That's possible, because `is_sent_start`
|
||
is only set to `True` for some of the tokens – all others still specify `None`
|
||
for unset sentence boundaries. This approach can be useful if you want to
|
||
implement **additional** rules specific to your data, while still being able to
|
||
take advantage of dependency-based sentence segmentation.
|
||
|
||
```python
|
||
### {executable="true"}
|
||
import spacy
|
||
|
||
text = "this is a sentence...hello...and another sentence."
|
||
|
||
nlp = spacy.load("en_core_web_sm")
|
||
doc = nlp(text)
|
||
print("Before:", [sent.text for sent in doc.sents])
|
||
|
||
def set_custom_boundaries(doc):
|
||
for token in doc[:-1]:
|
||
if token.text == "...":
|
||
doc[token.i+1].is_sent_start = True
|
||
return doc
|
||
|
||
nlp.add_pipe(set_custom_boundaries, before="parser")
|
||
doc = nlp(text)
|
||
print("After:", [sent.text for sent in doc.sents])
|
||
```
|
||
|
||
## Rule-based matching {#rule-based-matching hidden="true"}
|
||
|
||
<div id="rule-based-matching">
|
||
<Infobox title="📖 Rule-based matching" id="rule-based-matching">
|
||
|
||
The documentation on rule-based matching
|
||
[has moved to its own page](/usage/rule-based-matching).
|
||
|
||
</Infobox>
|
||
</div>
|