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Add development docs for Language and code conventions (#8745) 

* WIP: add dev docs for Language / config [ci skip]

* Add section on initialization [ci skip]

* Fix wording [ci skip]

* Add code conventions WIP [ci skip]

* Update code convention docs [ci skip]

* Update contributing guide and conventions [ci skip]

* Update Code Conventions.md [ci skip]

* Clarify sourced components + vectors

* Apply suggestions from code review [ci skip]

Co-authored-by: Sofie Van Landeghem <svlandeg@users.noreply.github.com>

* Update wording and add link [ci skip]

* restructure slightly + extended index

* remove paragraph that breaks flow and is repeated in more detail later

* fix anchors

Co-authored-by: Adriane Boyd <adrianeboyd@gmail.com>
Co-authored-by: Sofie Van Landeghem <svlandeg@users.noreply.github.com>
Co-authored-by: svlandeg <sofie.vanlandeghem@gmail.com>
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CONTRIBUTING.md
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@ -185,7 +185,6 @@ Each time a `git commit` is initiated, `black` and `flake8` will run automatical
In case of error, or when `black` modified a file, the modified file needs to be `git add` once again and a new
`git commit` has to be issued.
### Code formatting
[`black`](https://github.com/ambv/black) is an opinionated Python code
@ -414,14 +413,7 @@ all test files and test functions need to be prefixed with `test_`.
When adding tests, make sure to use descriptive names, keep the code short and
concise and only test for one behavior at a time. Try to `parametrize` test
cases wherever possible, use our pre-defined fixtures for spaCy components and
avoid unnecessary imports.
Extensive tests that take a long time should be marked with `@pytest.mark.slow`.
Tests that require the model to be loaded should be marked with
`@pytest.mark.models`. Loading the models is expensive and not necessary if
you're not actually testing the model performance. If all you need is a `Doc`
object with annotations like heads, POS tags or the dependency parse, you can
use the `Doc` constructor to construct it manually.
avoid unnecessary imports. Extensive tests that take a long time should be marked with `@pytest.mark.slow`.
📖 **For more guidelines and information on how to add tests, check out the [tests README](spacy/tests/README.md).**

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# Code Conventions
For a general overview of code conventions for contributors, see the [section in the contributing guide](https://github.com/explosion/spaCy/blob/master/CONTRIBUTING.md#code-conventions).
1. [Code compatibility](#code-compatibility)
2. [Auto-formatting](#auto-formatting)
3. [Linting](#linting)
4. [Documenting code](#documenting-code)
5. [Type hints](#type-hints)
6. [Structuring logic](#structuring-logic)
7. [Naming](#naming)
8. [Error handling](#error-handling)
9. [Writing tests](#writing-tests)
## Code compatibility
spaCy supports **Python 3.6** and above, so all code should be written compatible with 3.6. This means that there are certain new syntax features that we won't be able to use until we drop support for older Python versions. Some newer features provide backports that we can conditionally install for older versions, although we only want to do this if it's absolutely necessary. If we need to use conditional imports based on the Python version or other custom compatibility-specific helpers, those should live in `compat.py`.
## Auto-formatting
spaCy uses `black` for auto-formatting (which is also available as a pre-commit hook). It's recommended to configure your editor to perform this automatically, either triggered manually or whenever you save a file. We also have a GitHub action that regularly formats the code base and submits a PR if changes are available. Note that auto-formatting is currently only available for `.py` (Python) files, not for `.pyx` (Cython).
As a rule of thumb, if the auto-formatting produces output that looks messy, it can often indicate that there's a better way to structure the code to make it more concise.
```diff
- range_suggester = registry.misc.get("spacy.ngram_range_suggester.v1")(
- min_size=1, max_size=3
- )
+ suggester_factory = registry.misc.get("spacy.ngram_range_suggester.v1")
+ range_suggester = suggester_factory(min_size=1, max_size=3)
```
In some specific cases, e.g. in the tests, it can make sense to disable auto-formatting for a specific block. You can do this by wrapping the code in `# fmt: off` and `# fmt: on`:
```diff
+ # fmt: off
text = "I look forward to using Thingamajig. I've been told it will make my life easier..."
deps = ["nsubj", "ROOT", "advmod", "prep", "pcomp", "dobj", "punct", "",
"nsubjpass", "aux", "auxpass", "ROOT", "nsubj", "aux", "ccomp",
"poss", "nsubj", "ccomp", "punct"]
+ # fmt: on
```
## Linting
[`flake8`](http://flake8.pycqa.org/en/latest/) is a tool for enforcing code style. It scans one or more files and outputs errors and warnings. This feedback can help you stick to general standards and conventions, and can be very useful for spotting potential mistakes and inconsistencies in your code. Code you write should be compatible with our flake8 rules and not cause any warnings.
```bash
flake8 spacy
```
The most common problems surfaced by linting are:
- **Trailing or missing whitespace.** This is related to formatting and should be fixed automatically by running `black`.
- **Unused imports.** Those should be removed if the imports aren't actually used. If they're required, e.g. to expose them so they can be imported from the given module, you can add a comment and `# noqa: F401` exception (see details below).
- **Unused variables.** This can often indicate bugs, e.g. a variable that's declared and not correctly passed on or returned. To prevent ambiguity here, your code shouldn't contain unused variables. If you're unpacking a list of tuples and end up with variables you don't need, you can call them `_` to indicate that they're unused.
- **Redefinition of function.** This can also indicate bugs, e.g. a copy-pasted function that you forgot to rename and that now replaces the original function.
- **Repeated dictionary keys.** This either indicates a bug or unnecessary duplication.
- **Comparison with `True`, `False`, `None`**. This is mostly a stylistic thing: when checking whether a value is `True`, `False` or `None`, you should be using `is` instead of `==`. For example, `if value is None`.
### Ignoring linter rules for special cases
To ignore a given line, you can add a comment like `# noqa: F401`, specifying the code of the error or warning we want to ignore. It's also possible to ignore several comma-separated codes at once, e.g. `# noqa: E731,E123`. In general, you should always **specify the code(s)** you want to ignore – otherwise, you may end up missing actual problems.
```python
# The imported class isn't used in this file, but imported here, so it can be
# imported *from* here by another module.
from .submodule import SomeClass # noqa: F401
try:
do_something()
except: # noqa: E722
# This bare except is justified, for some specific reason
do_something_else()
```
## Documenting code
All functions and methods you write should be documented with a docstring inline. The docstring can contain a simple summary, and an overview of the arguments and their (simplified) types. Modern editors will show this information to users when they call the function or method in their code.
If it's part of the public API and there's a documentation section available, we usually add the link as `DOCS:` at the end. This allows us to keep the docstrings simple and concise, while also providing additional information and examples if necessary.
```python
def has_pipe(self, name: str) -> bool:
"""Check if a component name is present in the pipeline. Equivalent to
`name in nlp.pipe_names`.
name (str): Name of the component.
RETURNS (bool): Whether a component of the name exists in the pipeline.
DOCS: https://spacy.io/api/language#has_pipe
"""
...
```
We specifically chose this approach of maintaining the docstrings and API reference separately, instead of auto-generating the API docs from the docstrings like other packages do. We want to be able to provide extensive explanations and examples in the documentation and use our own custom markup for it that would otherwise clog up the docstrings. We also want to be able to update the documentation independently of the code base. It's slightly more work, but it's absolutely worth it in terms of user and developer experience.
### Inline code comments
We don't expect you to add inline comments for everything you're doing – this should be obvious from reading the code. If it's not, the first thing to check is whether your code can be improved to make it more explicit. That said, if your code includes complex logic or aspects that may be unintuitive at first glance (or even included a subtle bug that you ended up fixing), you should leave a quick comment that provides more context.
```diff
token_index = indices[value]
+ # Index describes Token.i of last token but Span indices are inclusive
span = doc[prev_token_index:token_index + 1]
```
```diff
+ # To create the components we need to use the final interpolated config
+ # so all values are available (if component configs use variables).
+ # Later we replace the component config with the raw config again.
interpolated = filled.interpolate() if not filled.is_interpolated else filled
```
Don't be shy about including comments for tricky parts that _you_ found hard to implement or get right – those may come in handy for the next person working on this code, or even future you!
If your change implements a fix to a specific issue, it can often be helpful to include the issue number in the comment, especially if it's a relatively straightforward adjustment:
```diff
+ # Ensure object is a Span, not a Doc (#1234)
if isinstance(obj, Doc):
obj = obj[obj.start:obj.end]
```
### Including TODOs
It's fine to include code comments that indicate future TODOs, using the `TODO:` prefix. Modern editors typically format this in a different color, so it's easy to spot. TODOs don't necessarily have to be things that are absolutely critical to fix fight now – those should already be addressed in your pull request once it's ready for review. But they can include notes about potential future improvements.
```diff
+ # TODO: this is currently pretty slow
dir_checksum = hashlib.md5()
for sub_file in sorted(fp for fp in path.rglob("*") if fp.is_file()):
dir_checksum.update(sub_file.read_bytes())
```
If any of the TODOs you've added are important and should be fixed soon, you should add a task for this on Explosion's internal Ora board or an issue on the public issue tracker to make sure we don't forget to address it.
## Type hints
We use Python type hints across the `.py` files wherever possible. This makes it easy to understand what a function expects and returns, and modern editors will be able to show this information to you when you call an annotated function. Type hints are not currently used in the `.pyx` (Cython) code, except for definitions of registered functions and component factories, where they're used for config validation.
If possible, you should always use the more descriptive type hints like `List[str]` or even `List[Any]` instead of only `list`. We also annotate arguments and return types of `Callable` – although, you can simplify this if the type otherwise gets too verbose (e.g. functions that return factories to create callbacks). Remember that `Callable` takes two values: a **list** of the argument type(s) in order, and the return values.
```diff
- def func(some_arg: dict) -> None:
+ def func(some_arg: Dict[str, Any]) -> None:
...
```
```python
def create_callback(some_arg: bool) -> Callable[[str, int], List[str]]:
def callback(arg1: str, arg2: int) -> List[str]:
...
return callback
```
For model architectures, Thinc also provides a collection of [custom types](https://thinc.ai/docs/api-types), including more specific types for arrays and model inputs/outputs. Even outside of static type checking, using these types will make the code a lot easier to read and follow, since it's always clear what array types are expected (and what might go wrong if the output is different from the expected type).
```python
def build_tagger_model(
tok2vec: Model[List[Doc], List[Floats2d]], nO: Optional[int] = None
) -> Model[List[Doc], List[Floats2d]]:
...
```
If you need to use a type hint that refers to something later declared in the same module, or the class that a method belongs to, you can use a string value instead:
```python
class SomeClass:
def from_bytes(self, data: bytes) -> "SomeClass":
...
```
In some cases, you won't be able to import a class from a different module to use it as a type hint because it'd cause circular imports. For instance, `spacy/util.py` includes various helper functions that return an instance of `Language`, but we couldn't import it, because `spacy/language.py` imports `util` itself. In this case, we can provide `"Language"` as a string and make the import conditional on `typing.TYPE_CHECKING` so it only runs when the code is evaluated by a type checker:
```python
from typing TYPE_CHECKING
if TYPE_CHECKING:
from .language import Language
def load_model(name: str) -> "Language":
...
```
## Structuring logic
### Positional and keyword arguments
We generally try to avoid writing functions and methods with too many arguments, and use keyword-only arguments wherever possible. Python lets you define arguments as keyword-only by separating them with a `, *`. If you're writing functions with additional arguments that customize the behavior, you typically want to make those arguments keyword-only, so their names have to be provided explicitly.
```diff
- def do_something(name: str, validate: bool = False):
+ def do_something(name: str, *, validate: bool = False):
...
- do_something("some_name", True)
+ do_something("some_name", validate=True)
```
This makes the function calls easier to read, because it's immediately clear what the additional values mean. It also makes it easier to extend arguments or change their order later on, because you don't end up with any function calls that depend on a specific positional order.
### Avoid mutable default arguments
A common Python gotcha are [mutable default arguments](https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments): if your argument defines a mutable default value like `[]` or `{}` and then goes and mutates it, the default value is created _once_ when the function is created and the same object is then mutated every time the function is called. This can be pretty unintuitive when you first encounter it. We therefore avoid writing logic that does this.
If your arguments need to default to an empty list or dict, you can use the `SimpleFrozenList` and `SimpleFrozenDict` helpers provided by spaCy. They are simple frozen implementations that raise an error if they're being mutated to prevent bugs and logic that accidentally mutates default arguments.
```diff
- def to_bytes(self, *, exclude: List[str] = []):
+ def to_bytes(self, *, exclude: List[str] = SimpleFrozenList()):
...
```
```diff
def do_something(values: List[str] = SimpleFrozenList()):
if some_condition:
- values.append("foo") # raises an error
+ values = [*values, "foo"]
return values
```
### Don't use `try`/`except` for control flow
We strongly discourage using `try`/`except` blocks for anything that's not third-party error handling or error handling that we otherwise have little control over. There's typically always a way to anticipate the _actual_ problem and **check for it explicitly**, which makes the code easier to follow and understand, and prevents bugs:
```diff
- try:
- token = doc[i]
- except IndexError:
- token = doc[-1]
+ if i < len(doc):
+ token = doc[i]
+ else:
+ token = doc[-1]
```
Even if you end up having to check for multiple conditions explicitly, this is still preferred over a catch-all `try`/`except`. It can be very helpful to think about the exact scenarios you need to cover, and what could go wrong at each step, which often leads to better code and fewer bugs. `try/except` blocks can also easily mask _other_ bugs and problems that raise the same errors you're catching, which is obviously bad.
If you have to use `try`/`except`, make sure to only include what's **absolutely necessary** in the `try` block and define the exception(s) explicitly. Otherwise, you may end up masking very different exceptions caused by other bugs.
```diff
- try:
- value1 = get_some_value()
- value2 = get_some_other_value()
- score = external_library.compute_some_score(value1, value2)
- except:
- score = 0.0
+ value1 = get_some_value()
+ value2 = get_some_other_value()
+ try:
+ score = external_library.compute_some_score(value1, value2)
+ except ValueError:
+ score = 0.0
```
### Avoid lambda functions
`lambda` functions can be useful for defining simple anonymous functions in a single line, but they also introduce problems: for instance, they require [additional logic](https://stackoverflow.com/questions/25348532/can-python-pickle-lambda-functions) in order to be pickled and are pretty ugly to type-annotate. So we typically avoid them in the code base and only use them in the serialization handlers and within tests for simplicity. Instead of `lambda`s, check if your code can be refactored to not need them, or use helper functions instead.
```diff
- split_string: Callable[[str], List[str]] = lambda value: [v.strip() for v in value.split(",")]
+ def split_string(value: str) -> List[str]:
+ return [v.strip() for v in value.split(",")]
```
### Iteration and comprehensions
We generally avoid using built-in functions like `filter` or `map` in favor of list or generator comprehensions.
```diff
- filtered = filter(lambda x: x in ["foo", "bar"], values)
+ filtered = (x for x in values if x in ["foo", "bar"])
- filtered = list(filter(lambda x: x in ["foo", "bar"], values))
+ filtered = [x for x in values if x in ["foo", "bar"]]
- result = map(lambda x: { x: x in ["foo", "bar"]}, values)
+ result = ({x: x in ["foo", "bar"]} for x in values)
- result = list(map(lambda x: { x: x in ["foo", "bar"]}, values))
+ result = [{x: x in ["foo", "bar"]} for x in values]
```
If your logic is more complex, it's often better to write a loop instead, even if it adds more lines of code in total. The result will be much easier to follow and understand.
```diff
- result = [{"key": key, "scores": {f"{i}": score for i, score in enumerate(scores)}} for key, scores in values]
+ result = []
+ for key, scores in values:
+ scores_dict = {f"{i}": score for i, score in enumerate(scores)}
+ result.append({"key": key, "scores": scores_dict})
```
### Composition vs. inheritance
Although spaCy uses a lot of classes, **inheritance is viewed with some suspicion** — it's seen as a mechanism of last resort. You should discuss plans to extend the class hierarchy before implementing. Unless you're implementing a new data structure or pipeline component, you typically shouldn't have to use classes at all.
### Don't use `print`
The core library never `print`s anything. While we encourage using `print` statements for simple debugging (it's the most straightforward way of looking at what's happening), make sure to clean them up once you're ready to submit your pull request. If you want to output warnings or debugging information for users, use the respective dedicated mechanisms for this instead (see sections on warnings and logging for details).
The only exceptions are the CLI functions, which pretty-print messages for the user, and methods that are explicitly intended for printing things, e.g. `Language.analyze_pipes` with `pretty=True` enabled. For this, we use our lightweight helper library [`wasabi`](https://github.com/ines/wasabi).
## Naming
Naming is hard and often a topic of long internal discussions. We don't expect you to come up with the perfect names for everything you write – finding the right names is often an iterative and collaborative process. That said, we do try to follow some basic conventions.
Consistent with general Python conventions, we use `CamelCase` for class names including dataclasses, `snake_case` for methods, functions and variables, and `UPPER_SNAKE_CASE` for constants, typically defined at the top of a module. We also avoid using variable names that shadow the names of built-in functions, e.g. `input`, `help` or `list`.
### Naming variables
Variable names should always make it clear _what exactly_ the variable is and what it's used for. Instances of common classes should use the same consistent names. For example, you should avoid naming a text string (or anything else that's not a `Doc` object) `doc`. The most common class-to-variable mappings are:
| Class | Variable | Example |
| ---------- | --------------------- | ------------------------------------------- |
| `Language` | `nlp` | `nlp = spacy.blank("en")` |
| `Doc` | `doc` | `doc = nlp("Some text")` |
| `Span` | `span`, `ent`, `sent` | `span = doc[1:4]`, `ent = doc.ents[0]` |
| `Token` | `token` | `token = doc[0]` |
| `Lexeme` | `lexeme`, `lex` | `lex = nlp.vocab["foo"]` |
| `Vocab` | `vocab` | `vocab = Vocab()` |
| `Example` | `example`, `eg` | `example = Example.from_dict(doc, gold)` |
| `Config` | `config`, `cfg` | `config = Config().from_disk("config.cfg")` |
We try to avoid introducing too many temporary variables, as these clutter your namespace. It's okay to re-assign to an existing variable, but only if the value has the same type.
```diff
ents = get_a_list_of_entities()
ents = [ent for ent in doc.ents if ent.label_ == "PERSON"]
- ents = {(ent.start, ent.end): ent.label_ for ent in ents}
+ ent_mappings = {(ent.start, ent.end): ent.label_ for ent in ents}
```
### Naming methods and functions
Try choosing short and descriptive names wherever possible and imperative verbs for methods that do something, e.g. `disable_pipes`, `add_patterns` or `get_vector`. Private methods and functions that are not intended to be part of the user-facing API should be prefixed with an underscore `_`. It's often helpful to look at the existing classes for inspiration.
Objects that can be serialized, e.g. data structures and pipeline components, should implement the same consistent methods for serialization. Those usually include at least `to_disk`, `from_disk`, `to_bytes` and `from_bytes`. Some objects can also implement more specific methods like `{to/from}_dict` or `{to/from}_str`.
## Error handling
We always encourage writing helpful and detailed custom error messages for everything we can anticipate going wrong, and including as much detail as possible. spaCy provides a directory of error messages in `errors.py` with unique codes for each message. This allows us to keep the code base more concise and avoids long and nested blocks of texts throughout the code that disrupt the reading flow. The codes make it easy to find references to the same error in different places, and also helps identify problems reported by users (since we can just search for the error code).
Errors can be referenced via their code, e.g. `Errors.E123`. Messages can also include placeholders for values, that can be populated by formatting the string with `.format()`.
```python
class Errors:
E123 = "Something went wrong"
E456 = "Unexpected value: {value}"
```
```diff
if something_went_wrong:
- raise ValueError("Something went wrong!")
+ raise ValueError(Errors.E123)
if not isinstance(value, int):
- raise ValueError(f"Unexpected value: {value}")
+ raise ValueError(Errors.E456.format(value=value))
```
As a general rule of thumb, all error messages raised within the **core library** should be added to `Errors`. The only place where we write errors and messages as strings is `spacy.cli`, since these functions typically pretty-print and generate a lot of output that'd otherwise be very difficult to separate from the actual logic.
### Re-raising exceptions
If we anticipate possible errors in third-party code that we don't control, or our own code in a very different context, we typically try to provide custom and more specific error messages if possible. If we need to re-raise an exception within a `try`/`except` block, we can re-raise a custom exception.
[Re-raising `from`](https://docs.python.org/3/tutorial/errors.html#exception-chaining) the original caught exception lets us chain the exceptions, so the user sees both the original error, as well as the custom message with a note "The above exception was the direct cause of the following exception".
```diff
try:
run_third_party_code_that_might_fail()
except ValueError as e:
+ raise ValueError(Errors.E123) from e
```
In some cases, it makes sense to suppress the original exception, e.g. if we know what it is and know that it's not particularly helpful. In that case, we can raise `from None`. This prevents clogging up the user's terminal with multiple and irrelevant chained exceptions.
```diff
try:
run_our_own_code_that_might_fail_confusingly()
except ValueError:
+ raise ValueError(Errors.E123) from None
```
### Avoid using naked `assert`
During development, it can sometimes be helpful to add `assert` statements throughout your code to make sure that the values you're working with are what you expect. However, as you clean up your code, those should either be removed or replaced by more explicit error handling:
```diff
- assert score >= 0.0
+ if score < 0.0:
+ raise ValueError(Errors.789.format(score=score))
```
Otherwise, the user will get to see a naked `AssertionError` with no further explanation, which is very unhelpful. Instead of adding an error message to `assert`, it's always better to `raise` more explicit errors for specific conditions. If you're checking for something that _has to be right_ and would otherwise be a bug in spaCy, you can express this in the error message:
```python
E161 = ("Found an internal inconsistency when predicting entity links. "
"This is likely a bug in spaCy, so feel free to open an issue: "
"https://github.com/explosion/spaCy/issues")
```
### Warnings
Instead of raising an error, some parts of the code base can raise warnings to notify the user of a potential problem. This is done using Python's `warnings.warn` and the messages defined in `Warnings` in the `errors.py`. Whether or not warnings are shown can be controlled by the user, including custom filters for disabling specific warnings using a regular expression matching our internal codes, e.g. `W123`.
```diff
- print("Warning: No examples provided for validation")
+ warnings.warn(Warnings.W123)
```
When adding warnings, make sure you're not calling `warnings.warn` repeatedly, e.g. in a loop, which will clog up the terminal output. Instead, you can collect the potential problems first and then raise a single warning. If the problem is critical, consider raising an error instead.
```diff
+ n_empty = 0
for spans in lots_of_annotations:
if len(spans) == 0:
- warnings.warn(Warnings.456)
+ n_empty += 1
+ warnings.warn(Warnings.456.format(count=n_empty))
```
### Logging
Log statements can be added via spaCy's `logger`, which uses Python's native `logging` module under the hood. We generally only use logging for debugging information that **the user may choose to see** in debugging mode or that's **relevant during training** but not at runtime.
```diff
+ logger.info("Set up nlp object from config")
config = nlp.config.interpolate()
```
`spacy train` and similar CLI commands will enable all log statements of level `INFO` by default (which is not the case at runtime). This allows outputting specific information within certain parts of the core library during training, without having it shown at runtime. `DEBUG`-level logs are only shown if the user enables `--verbose` logging during training. They can be used to provide more specific and potentially more verbose details, especially in areas that can indicate bugs or problems, or to surface more details about what spaCy does under the hood. You should only use logging statements if absolutely necessary and important.
## Writing tests
spaCy uses the [`pytest`](http://doc.pytest.org/) framework for testing. Tests for spaCy modules and classes live in their own directories of the same name and all test files should be prefixed with `test_`. Tests included in the core library only cover the code and do not depend on any trained pipelines. When implementing a new feature or fixing a bug, it's usually good to start by writing some tests that describe what _should_ happen. As you write your code, you can then keep running the relevant tests until all of them pass.
### Test suite structure
When adding tests, make sure to use descriptive names and only test for one behavior at a time. Tests should be grouped into modules dedicated to the same type of functionality and some test modules are organized as directories of test files related to the same larger area of the library, e.g. `matcher` or `tokenizer`.
Regression tests are tests that refer to bugs reported in specific issues. They should live in the `regression` module and are named according to the issue number (e.g. `test_issue1234.py`). This system allows us to relate tests for specific bugs back to the original reported issue, which is especially useful if we introduce a regression and a previously passing regression tests suddenly fails again. When fixing a bug, it's often useful to create a regression test for it first. Every once in a while, we go through the `regression` module and group tests together into larger files by issue number, in groups of 500 to 1000 numbers. This prevents us from ending up with too many individual files over time.
The test suite also provides [fixtures](https://github.com/explosion/spaCy/blob/master/spacy/tests/conftest.py) for different language tokenizers that can be used as function arguments of the same name and will be passed in automatically. Those should only be used for tests related to those specific languages. We also have [test utility functions](https://github.com/explosion/spaCy/blob/master/spacy/tests/util.py) for common operations, like creating a temporary file.
### Constructing objects and state
Test functions usually follow the same simple structure: they set up some state, perform the operation you want to test and `assert` conditions that you expect to be true, usually before and after the operation.
Tests should focus on exactly what they're testing and avoid dependencies on other unrelated library functionality wherever possible. If all your test needs is a `Doc` object with certain annotations set, you should always construct it manually:
```python
def test_doc_creation_with_pos():
doc = Doc(Vocab(), words=["hello", "world"], pos=["NOUN", "VERB"])
assert doc[0].pos_ == "NOUN"
assert doc[1].pos_ == "VERB"
```
### Parametrizing tests
If you need to run the same test function over different input examples, you usually want to parametrize the test cases instead of using a loop within your test. This lets you keep a better separation between test cases and test logic, and it'll result in more useful output because `pytest` will be able to tell you which exact test case failed.
The `@pytest.mark.parametrize` decorator takes two arguments: a string defining one or more comma-separated arguments that should be passed to the test function and a list of corresponding test cases (or a list of tuples to provide multiple arguments).
```python
@pytest.mark.parametrize("words", [["hello", "world"], ["this", "is", "a", "test"]])
def test_doc_length(words):
doc = Doc(Vocab(), words=words)
assert len(doc) == len(words)
```
```python
@pytest.mark.parametrize("text,expected_len", [("hello world", 2), ("I can't!", 4)])
def test_token_length(en_tokenizer, text, expected_len): # en_tokenizer is a fixture
doc = en_tokenizer(text)
assert len(doc) == expected_len
```
You can also stack `@pytest.mark.parametrize` decorators, although this is not recommended unless it's absolutely needed or required for the test. When stacking decorators, keep in mind that this will run the test with all possible combinations of the respective parametrized values, which is often not what you want and can slow down the test suite.
### Handling failing tests
`xfail` means that a test **should pass but currently fails**, i.e. is expected to fail. You can mark a test as currently xfailing by adding the `@pytest.mark.xfail` decorator. This should only be used for tests that don't yet work, not for logic that cause errors we raise on purpose (see the section on testing errors for this). It's often very helpful to implement tests for edge cases that we don't yet cover and mark them as `xfail`. You can also provide a `reason` keyword argument to the decorator with an explanation of why the test currently fails.
```diff
+ @pytest.mark.xfail(reason="Issue #225 - not yet implemented")
def test_en_tokenizer_splits_em_dash_infix(en_tokenizer):
doc = en_tokenizer("Will this road take me to Puddleton?\u2014No.")
assert doc[8].text == "\u2014"
```
When you run the test suite, you may come across tests that are reported as `xpass`. This means that they're marked as `xfail` but didn't actually fail. This is worth looking into: sometimes, it can mean that we have since fixed a bug that caused the test to previously fail, so we can remove the decorator. In other cases, especially when it comes to machine learning model implementations, it can also indicate that the **test is flaky**: it sometimes passes and sometimes fails. This can be caused by a bug, or by constraints being too narrowly defined. If a test shows different behavior depending on whether its run in isolation or not, this can indicate that it reacts to global state set in a previous test, which is unideal and should be avoided.
### Writing slow tests
If a test is useful but potentially quite slow, you can mark it with the `@pytest.mark.slow` decorator. This is a special marker we introduced and tests decorated with it only run if you run the test suite with `--slow`, but not as part of the main CI process. Before introducing a slow test, double-check that there isn't another and more efficient way to test for the behavior. You should also consider adding a simpler test with maybe only a subset of the test cases that can always run, so we at least have some coverage.
### Skipping tests
The `@pytest.mark.skip` decorator lets you skip tests entirely. You only want to do this for failing tests that may be slow to run or cause memory errors or segfaults, which would otherwise terminate the entire process and wouldn't be caught by `xfail`. We also sometimes use the `skip` decorator for old and outdated regression tests that we want to keep around but that don't apply anymore. When using the `skip` decorator, make sure to provide the `reason` keyword argument with a quick explanation of why you chose to skip this test.
### Testing errors and warnings
`pytest` lets you check whether a given error is raised by using the `pytest.raises` contextmanager. This is very useful when implementing custom error handling, so make sure you're not only testing for the correct behavior but also for errors resulting from incorrect inputs. If you're testing errors, you should always check for `pytest.raises` explicitly and not use `xfail`.
```python
words = ["a", "b", "c", "d", "e"]
ents = ["Q-PERSON", "I-PERSON", "O", "I-PERSON", "I-GPE"]
with pytest.raises(ValueError):
Doc(Vocab(), words=words, ents=ents)
```
You can also use the `pytest.warns` contextmanager to check that a given warning type is raised. The first argument is the warning type or `None` (which will capture a list of warnings that you can `assert` is empty).
```python
def test_phrase_matcher_validation(en_vocab):
doc1 = Doc(en_vocab, words=["Test"], deps=["ROOT"])
doc2 = Doc(en_vocab, words=["Test"])
matcher = PhraseMatcher(en_vocab, validate=True)
with pytest.warns(UserWarning):
# Warn about unnecessarily parsed document
matcher.add("TEST1", [doc1])
with pytest.warns(None) as record:
matcher.add("TEST2", [docs])
assert not record.list
```
Keep in mind that your tests will fail if you're using the `pytest.warns` contextmanager with a given warning and the warning is _not_ shown. So you should only use it to check that spaCy handles and outputs warnings correctly. If your test outputs a warning that's expected but not relevant to what you're testing, you can use the `@pytest.mark.filterwarnings` decorator and ignore specific warnings starting with a given code:
```python
@pytest.mark.filterwarnings("ignore:\\[W036")
def test_matcher_empty(en_vocab):
matcher = Matcher(en_vocab)
matcher(Doc(en_vocab, words=["test"]))
```
### Testing trained pipelines
Our regular test suite does not depend on any of the trained pipelines, since their outputs can vary and aren't generally required to test the library functionality. We test pipelines separately using the tests included in the [`spacy-models`](https://github.com/explosion/spacy-models) repository, which run whenever we train a new suite of models. The tests here mostly focus on making sure that the packages can be loaded and that the predictions seam reasonable, and they include checks for common bugs we encountered previously. If your test does not primarily focus on verifying a model's predictions, it should be part of the core library tests and construct the required objects manually, instead of being added to the models tests.
Keep in mind that specific predictions may change, and we can't test for all incorrect predictions reported by users. Different models make different mistakes, so even a model that's significantly more accurate overall may end up making wrong predictions that it previously didn't. However, some surprising incorrect predictions may indicate deeper bugs that we definitely want to investigate.

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# Language
> Reference: `spacy/language.py`
1. [Constructing the `nlp` object from a config](#1-constructing-the-nlp-object-from-a-config)
- [A. Overview of `Language.from_config`](#1a-overview)
- [B. Component factories](#1b-how-pipeline-component-factories-work-in-the-config)
- [C. Sourcing a component](#1c-sourcing-a-pipeline-component)
- [D. Tracking components as they're modified](#1d-tracking-components-as-theyre-modified)
- [E. spaCy's config utility function](#1e-spacys-config-utility-functions)
2. [Initialization](#initialization)
- [A. Initialization for training](#2a-initialization-for-training): `init_nlp`
- [B. Initializing the `nlp` object](#2b-initializing-the-nlp-object): `Language.initialize`
- [C. Initializing the vocab](#2c-initializing-the-vocab): `init_vocab`
## 1. Constructing the `nlp` object from a config
### 1A. Overview
Most of the functions referenced in the config are regular functions with arbitrary arguments registered via the function registry. However, the pipeline components are a bit special: they don't only receive arguments passed in via the config file, but also the current `nlp` object and the string `name` of the individual component instance (so a user can have multiple components created with the same factory, e.g. `ner_one` and `ner_two`). This name can then be used by the components to add to the losses and scores. This special requirement means that pipeline components can't just be resolved via the config the "normal" way: we need to retrieve the component functions manually and pass them their arguments, plus the `nlp` and `name`.
The `Language.from_config` classmethod takes care of constructing the `nlp` object from a config. It's the single place where this happens and what `spacy.load` delegates to under the hood. Its main responsibilities are:
- **Load and validate the config**, and optionally **auto-fill** all missing values that we either have defaults for in the config template or that registered function arguments define defaults for. This helps ensure backwards-compatibility, because we're able to add a new argument `foo: str = "bar"` to an existing function, without breaking configs that don't specity it.
- **Execute relevant callbacks** for pipeline creation, e.g. optional functions called before and after creation of the `nlp` object and pipeline.
- **Initialize language subclass and create tokenizer**. The `from_config` classmethod will always be called on a language subclass, e.g. `English`, not on `Language` directly. Initializing the subclass takes a callback to create the tokenizer.
- **Set up the pipeline components**. Components can either refer to a component factory or a `source`, i.e. an existing pipeline that's loaded and that the component is then copied from. We also need to ensure that we update the information about which components are disabled.
- **Manage listeners.** If sourced components "listen" to other components (`tok2vec`, `transformer`), we need to ensure that the references are valid. If the config specifies that listeners should be replaced by copies (e.g. to give the `ner` component its own `tok2vec` model instead of listening to the shared `tok2vec` component in the pipeline), we also need to take care of that.
Note that we only resolve and load **selected sections** in `Language.from_config`, i.e. only the parts that are relevant at runtime, which is `[nlp]` and `[components]`. We don't want to be resolving anything related to training or initialization, since this would mean loading and constructing unnecessary functions, including functions that require information that isn't necessarily available at runtime, like `paths.train`.
### 1B. How pipeline component factories work in the config
As opposed to regular registered functions that refer to a registry and function name (e.g. `"@misc": "foo.v1"`), pipeline components follow a different format and refer to their component `factory` name. This corresponds to the name defined via the `@Language.component` or `@Language.factory` decorator. We need this decorator to define additional meta information for the components, like their default config and score weights.
```ini
[components.my_component]
factory = "foo"
some_arg = "bar"
other_arg = ${paths.some_path}
```
This means that we need to create and resolve the `config["components"]` separately from the rest of the config. There are some important considerations and things we need to manage explicitly to avoid unexpected behavior:
#### Variable interpolation
When a config is resolved, references to variables are replaced, so that the functions receive the correct value instead of just the variable name. To interpolate a config, we need it in its entirety: we couldn't just interpolate a subsection that refers to variables defined in a different subsection. So we first interpolate the entire config.
However, the `nlp.config` should include the original config with variables intact – otherwise, loading a pipeline and saving it to disk will destroy all logic implemented via variables and hard-code the values all over the place. This means that when we create the components, we need to keep two versions of the config: the interpolated config with the "real" values and the `raw_config` including the variable references.
#### Factory registry
Component factories are special and use the `@Language.factory` or `@Language.component` decorator to register themselves and their meta. When the decorator runs, it performs some basic validation, stores the meta information for the factory on the `Language` class (default config, scores etc.) and then adds the factory function to `registry.factories`. The `component` decorator can be used for registering simple functions that just take a `Doc` object and return it so in that case, we create the factory for the user automatically.
There's one important detail to note about how factories are registered via entry points: A package that wants to expose spaCy components still needs to register them via the `@Language` decorators so we have the component meta information and can perform required checks. All we care about here is that the decorated function is **loaded and imported**. When it is, the `@Language` decorator takes care of everything, including actually registering the component factory.
Normally, adding to the registry via an entry point will just add the function to the registry under the given name. But for `spacy_factories`, we don't actually want that: all we care about is that the function decorated with `@Language` is imported so the decorator runs. So we only exploit Python's entry point system to automatically import the function, and the `spacy_factories` entry point group actually adds to a **separate registry**, `registry._factories`, under the hood. Its only purpose is that the functions are imported. The decorator then runs, creates the factory if needed and adds it to the `registry.factories` registry.
#### Language-specific factories
spaCy supports registering factories on the `Language` base class, as well as language-specific subclasses like `English` or `German`. This allows providing different factories depending on the language, e.g. a different default lemmatizer. The `Language.get_factory_name` classmethod constructs the factory name as `{lang}.{name}` if a language is available (i.e. if it's a subclass) and falls back to `{name}` otherwise. So `@German.factory("foo")` will add a factory `de.foo` under the hood. If you add `nlp.add_pipe("foo")`, we first check if there's a factory for `{nlp.lang}.foo` and if not, we fall back to checking for a factory `foo`.
#### Creating a pipeline component from a factory
`Language.add_pipe` takes care of adding a pipeline component, given its factory name, its config. If no source pipeline to copy the component from is provided, it delegates to `Language.create_pipe`, which sets up the actual component function.
- Validate the config and make sure that the factory was registered via the decorator and that we have meta for it.
- Update the component config with any defaults specified by the component's `default_config`, if available. This is done by merging the values we receive into the defaults. It ensures that you can still add a component without having to specify its _entire_ config including more complex settings like `model`. If no `model` is defined, we use the default.
- Check if we have a language-specific factory for the given `nlp.lang` and if not, fall back to the global factory.
- Construct the component config, consisting of whatever arguments were provided, plus the current `nlp` object and `name`, which are default expected arguments of all factories. We also add a reference to the `@factories` registry, so we can resolve the config via the registry, like any other config. With the added `nlp` and `name`, it should now include all expected arguments of the given function.
- Fill the config to make sure all unspecified defaults from the function arguments are added and update the `raw_config` (uninterpolated with variables intact) with that information, so the component config we store in `nlp.config` is up to date. We do this by adding the `raw_config` _into_ the filled config – otherwise, the references to variables would be overwritten.
- Resolve the config and create all functions it refers to (e.g. `model`). This gives us the actual component function that we can insert into the pipeline.
### 1C. Sourcing a pipeline component
```ini
[components.ner]
source = "en_core_web_sm"
```
spaCy also allows ["sourcing" a component](https://spacy.io/usage/processing-pipelines#sourced-components), which will copy it over from an existing pipeline. In this case, `Language.add_pipe` will delegate to `Language.create_pipe_from_source`. In order to copy a component effectively and validate it, the source pipeline first needs to be loaded. This is done in `Language.from_config`, so a source pipeline only has to be loaded once if multiple components source from it. Sourcing a component will perform the following checks and modifications:
- For each sourced pipeline component loaded in `Language.from_config`, a hash of the vectors data from the source pipeline is stored in the pipeline meta so we're able to check whether the vectors match and warn if not (since different vectors that are used as features in components can lead to degraded performance). Because the vectors are not loaded at the point when components are sourced, the check is postponed to `init_vocab` as part of `Language.initialize`.
- If the sourced pipeline component is loaded through `Language.add_pipe(source=)`, the vectors are already loaded and can be compared directly. The check compares the shape and keys first and finally falls back to comparing the actual byte representation of the vectors (which is slower).
- Ensure that the component is available in the pipeline.
- Interpolate the entire config of the source pipeline so all variables are replaced and the component's config that's copied over doesn't include references to variables that are not available in the destination config.
- Add the source `vocab.strings` to the destination's `vocab.strings` so we don't end up with unavailable strings in the final pipeline (which would also include labels used by the sourced component).
Note that there may be other incompatibilities that we're currently not checking for and that could cause a sourced component to not work in the destination pipeline. We're interested in adding more checks here but there'll always be a small number of edge cases we'll never be able to catch, including a sourced component depending on other pipeline state that's not available in the destination pipeline.
### 1D. Tracking components as they're modified
The `Language` class implements methods for removing, replacing or renaming pipeline components. Whenever we make these changes, we need to update the information stored on the `Language` object to ensure that it matches the current state of the pipeline. If a user just writes to `nlp.config` manually, we obviously can't ensure that the config matches the reality – but since we offer modification via the pipe methods, it's expected that spaCy keeps the config in sync under the hood. Otherwise, saving a modified pipeline to disk and loading it back wouldn't work. The internal attributes we need to keep in sync here are:
| Attribute | Type | Description |
| ------------------------ | ---------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `Language._components` | `List[Tuple[str, Callable]]` | All pipeline components as `(name, func)` tuples. This is used as the source of truth for `Language.pipeline`, `Language.pipe_names` and `Language.components`. |
| `Language._pipe_meta` | `Dict[str, FactoryMeta]` | The meta information of a component's factory, keyed by component name. This can include multiple components referring to the same factory meta. |
| `Language._pipe_configs` | `Dict[str, Config]` | The component's config, keyed by component name. |
| `Language._disabled` | `Set[str]` | Names of components that are currently disabled. |
| `Language._config` | `Config` | The underlying config. This is only internals and will be used as the basis for constructing the config in the `Language.config` property. |
In addition to the actual component settings in `[components]`, the config also allows specifying component-specific arguments via the `[initialize.components]` block, which are passed to the component's `initialize` method during initialization if it's available. So we also need to keep this in sync in the underlying config.
### 1E. spaCy's config utility functions
When working with configs in spaCy, make sure to use the utility functions provided by spaCy if available, instead of calling the respective `Config` methods. The utilities take care of providing spaCy-specific error messages and ensure a consistent order of config sections by setting the `section_order` argument. This ensures that exported configs always have the same consistent format.
- `util.load_config`: load a config from a file
- `util.load_config_from_str`: load a confirm from a string representation
- `util.copy_config`: deepcopy a config
## 2. Initialization
Initialization is a separate step of the [config lifecycle](https://spacy.io/usage/training#config-lifecycle) that's not performed at runtime. It's implemented via the `training.initialize.init_nlp` helper and calls into `Language.initialize` method, which sets up the pipeline and component models before training. The `initialize` method takes a callback that returns a sample of examples, which is used to initialize the component models, add all required labels and perform shape inference if applicable.
Components can also define custom initialization setting via the `[initialize.components]` block, e.g. if they require external data like lookup tables to be loaded in. All config settings defined here will be passed to the component's `initialize` method, if it implements one. Components are expected to handle their own serialization after they're initialized so that any data or settings they require are saved with the pipeline and will be available from disk when the pipeline is loaded back at runtime.
### 2A. Initialization for training
The `init_nlp` function is called before training and returns an initialized `nlp` object that can be updated with the examples. It only needs the config and does the following:
- Load and validate the config. In order to validate certain settings like the `seed`, we also interpolate the config to get the final value (because in theory, a user could provide this via a variable).
- Set up the GPU allocation, if required.
- Create the `nlp` object from the raw, uninterpolated config, which delegates to `Language.from_config`. Since this method may modify and auto-fill the config and pipeline component settings, we then use the interpolated version of `nlp.config` going forward, to ensure that what we're training with is up to date.
- Resolve the `[training]` block of the config and perform validation, e.g. to check that the corpora are available.
- Determine the components that should be frozen (not updated during training) or resumed (sourced components from a different pipeline that should be updated from the examples and not reset and re-initialized). To resume training, we can call the `nlp.resume_training` method.
- Initialize the `nlp` object via `nlp.initialize` and pass it a `get_examples` callback that returns the training corpus (used for shape inference, setting up labels etc.). If the training corpus is streamed, we only provide a small sample of the data, which can potentially be infinite. `nlp.initialize` will delegate to the components as well and pass the data sample forward.
- Check the listeners and warn about components dependencies, e.g. if a frozen component listens to a component that is retrained, or vice versa (which can degrade results).
### 2B. Initializing the `nlp` object
The `Language.initialize` method does the following:
- **Resolve the config** defined in the `[initialize]` block separately (since everything else is already available in the loaded `nlp` object), based on the fully interpolated config.
- **Execute callbacks**, i.e. `before_init` and `after_init`, if they're defined.
- **Initialize the vocab**, including vocab data, lookup tables and vectors.
- **Initialize the tokenizer** if it implements an `initialize` method. This is not the case for the default tokenizers, but it allows custom tokenizers to depend on external data resources that are loaded in on initialization.
- **Initialize all pipeline components** if they implement an `initialize` method and pass them the `get_examples` callback, the current `nlp` object as well as well additional initialization config settings provided in the component-specific block.
- **Initialize pretraining** if a `[pretraining]` block is available in the config. This allows loading pretrained tok2vec weights in `spacy pretrain`.
- **Register listeners** if token-to-vector embedding layers of a component model "listen" to a previous component (`tok2vec`, `transformer`) in the pipeline.
- **Create an optimizer** on the `Language` class, either by adding the optimizer passed as `sgd` to `initialize`, or by creating the optimizer defined in the config's training settings.
### 2C. Initializing the vocab
Vocab initialization is handled in the `training.initialize.init_vocab` helper. It takes the relevant loaded functions and values from the config and takes care of the following:
- Add lookup tables defined in the config initialization, e.g. custom lemmatization tables. Those will be added to `nlp.vocab.lookups` from where they can be accessed by components.
- Add JSONL-formatted [vocabulary data](https://spacy.io/api/data-formats#vocab-jsonl) to pre-populate the lexical attributes.
- Load vectors into the pipeline. Vectors are defined as a name or path to a saved `nlp` object containing the vectors, e.g. `en_vectors_web_lg`. It's loaded and the vectors are ported over, while ensuring that all source strings are available in the destination strings. We also warn if there's a mismatch between sourced vectors, since this can lead to problems.

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<a href="https://explosion.ai"><img src="https://explosion.ai/assets/img/logo.svg" width="125" height="125" align="right" /></a>
# Developer Documentation
This directory includes additional documentation and explanations of spaCy's internals. It's mostly intended for the spaCy core development team and contributors interested in the more complex parts of the library. The documents generally focus on more abstract implementation details and how specific methods and algorithms work, and they assume knowledge of what's already available in the [usage documentation](https://spacy.io/usage) and [API reference](https://spacy.io/api).
If you're looking to contribute to spaCy, make sure to check out the documentation and [contributing guide](https://github.com/explosion/spaCy/blob/master/CONTRIBUTING.md) first.