Add `CommaSeparatedStrings` datatype (#274)

* Add CommaSeparatedStrings datatype

* Version 0.9.9

docs/config.md

@@ -9,7 +9,7 @@ that is not committed to source control.
 ```python
 from starlette.applications import Starlette
 from starlette.config import Config
-from starlette.datastructures import DatabaseURL, Secret
+from starlette.datastructures import CommaSeparatedStrings, DatabaseURL, Secret
 
 # Config will be read from environment variables and/or ".env" files.
 config = Config(".env")
@@ -17,6 +17,7 @@ config = Config(".env")
 DEBUG = config('DEBUG', cast=bool, default=False)
 DATABASE_URL = config('DATABASE_URL', cast=DatabaseURL)
 SECRET_KEY = config('SECRET_KEY', cast=Secret)
+ALLOWED_HOSTS = config('ALLOWED_HOSTS', cast=CommaSeparatedStrings)
 
 app = Starlette()
 app.debug = DEBUG
@@ -31,6 +32,7 @@ app.debug = DEBUG
 DEBUG=True
 DATABASE_URL=postgresql://localhost/myproject
 SECRET_KEY=43n080musdfjt54t-09sdgr
+ALLOWED_HOSTS="127.0.0.1", "localhost"
 ```
 
 ## Configuration precedence
@@ -45,8 +47,8 @@ If none of those match, then `config(...)` will raise an error.
 
 ## Secrets
 
-For sensitive keys, the `Secret` class is useful, since it prevents the value from
+For sensitive keys, the `Secret` class is useful, since it helps minimize
-leaking out into tracebacks or logging.
+occasions where the value it holds could leak out into tracebacks or logging.
 
 To get the value of a `Secret` instance, you must explicitly cast it to a string.
 You should only do this at the point at which the value is used.

starlette/__init__.py

@@ -1 +1 @@
-__version__ = "0.9.8"
+__version__ = "0.9.9"

starlette/datastructures.py

@@ -1,5 +1,7 @@
 import typing
 from collections import namedtuple
+from collections.abc import Sequence
+from shlex import shlex
 from urllib.parse import ParseResult, parse_qsl, urlencode, urlparse
 
 from starlette.types import Scope
@@ -195,6 +197,33 @@ class Secret:
         return self._value
 
 
+class CommaSeparatedStrings(Sequence):
+    def __init__(self, value: typing.Union[str, typing.Sequence[str]]):
+        if isinstance(value, str):
+            splitter = shlex(value, posix=True)
+            splitter.whitespace = ","
+            splitter.whitespace_split = True
+            self._items = [item.strip() for item in splitter]
+        else:
+            self._items = list(value)
+
+    def __len__(self) -> int:
+        return len(self._items)
+
+    def __getitem__(self, index: typing.Union[int, slice]) -> typing.Any:
+        return self._items[index]
+
+    def __iter__(self) -> typing.Iterator[str]:
+        return iter(self._items)
+
+    def __repr__(self) -> str:
+        list_repr = repr([item for item in self])
+        return "%s(%s)" % (self.__class__.__name__, list_repr)
+
+    def __str__(self) -> str:
+        return ", ".join([repr(item) for item in self])
+
+
 class QueryParams(typing.Mapping[str, str]):
     """
     An immutable multidict.

tests/test_datastructures.py

@@ -1,5 +1,6 @@
 from starlette.datastructures import (
     URL,
+    CommaSeparatedStrings,
     DatabaseURL,
     Headers,
     MutableHeaders,
@@ -59,6 +60,30 @@ def test_database_url():
     assert u.driver == "asyncpg"
 
 
+def test_csv():
+    csv = CommaSeparatedStrings('"localhost", "127.0.0.1", 0.0.0.0')
+    assert list(csv) == ["localhost", "127.0.0.1", "0.0.0.0"]
+    assert repr(csv) == "CommaSeparatedStrings(['localhost', '127.0.0.1', '0.0.0.0'])"
+    assert str(csv) == "'localhost', '127.0.0.1', '0.0.0.0'"
+    assert csv[0] == "localhost"
+    assert len(csv) == 3
+
+    csv = CommaSeparatedStrings("'localhost', '127.0.0.1', 0.0.0.0")
+    assert list(csv) == ["localhost", "127.0.0.1", "0.0.0.0"]
+    assert repr(csv) == "CommaSeparatedStrings(['localhost', '127.0.0.1', '0.0.0.0'])"
+    assert str(csv) == "'localhost', '127.0.0.1', '0.0.0.0'"
+
+    csv = CommaSeparatedStrings("localhost, 127.0.0.1, 0.0.0.0")
+    assert list(csv) == ["localhost", "127.0.0.1", "0.0.0.0"]
+    assert repr(csv) == "CommaSeparatedStrings(['localhost', '127.0.0.1', '0.0.0.0'])"
+    assert str(csv) == "'localhost', '127.0.0.1', '0.0.0.0'"
+
+    csv = CommaSeparatedStrings(["localhost", "127.0.0.1", "0.0.0.0"])
+    assert list(csv) == ["localhost", "127.0.0.1", "0.0.0.0"]
+    assert repr(csv) == "CommaSeparatedStrings(['localhost', '127.0.0.1', '0.0.0.0'])"
+    assert str(csv) == "'localhost', '127.0.0.1', '0.0.0.0'"
+
+
 def test_url_from_scope():
     u = URL(
         scope={"path": "/path/to/somewhere", "query_string": b"abc=123", "headers": []}