annotations.po

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#: ../../howto/annotations.rst:5
msgid "Annotations Best Practices"
msgstr ""

#: ../../howto/annotations.rst:0
msgid "author"
msgstr "author"

#: ../../howto/annotations.rst:7
msgid "Larry Hastings"
msgstr "Larry Hastings"

#: ../../howto/annotations.rst-1
msgid "Abstract"
msgstr "概要"

#: ../../howto/annotations.rst:11
msgid ""
"This document is designed to encapsulate the best practices for working with "
"annotations dicts.  If you write Python code that examines "
"``__annotations__`` on Python objects, we encourage you to follow the "
"guidelines described below."
msgstr ""

#: ../../howto/annotations.rst:16
msgid ""
"The document is organized into four sections: best practices for accessing "
"the annotations of an object in Python versions 3.10 and newer, best "
"practices for accessing the annotations of an object in Python versions 3.9 "
"and older, other best practices for ``__annotations__`` that apply to any "
"Python version, and quirks of ``__annotations__``."
msgstr ""

#: ../../howto/annotations.rst:26
msgid ""
"Note that this document is specifically about working with "
"``__annotations__``, not uses *for* annotations. If you're looking for "
"information on how to use \"type hints\" in your code, please see the :mod:"
"`typing` module."
msgstr ""

#: ../../howto/annotations.rst:33
msgid "Accessing The Annotations Dict Of An Object In Python 3.10 And Newer"
msgstr ""

#: ../../howto/annotations.rst:35
msgid ""
"Python 3.10 adds a new function to the standard library: :func:`inspect."
"get_annotations`.  In Python versions 3.10 and newer, calling this function "
"is the best practice for accessing the annotations dict of any object that "
"supports annotations.  This function can also \"un-stringize\" stringized "
"annotations for you."
msgstr ""

#: ../../howto/annotations.rst:42
msgid ""
"If for some reason :func:`inspect.get_annotations` isn't viable for your use "
"case, you may access the ``__annotations__`` data member manually.  Best "
"practice for this changed in Python 3.10 as well: as of Python 3.10, ``o."
"__annotations__`` is guaranteed to *always* work on Python functions, "
"classes, and modules.  If you're certain the object you're examining is one "
"of these three *specific* objects, you may simply use ``o.__annotations__`` "
"to get at the object's annotations dict."
msgstr ""

#: ../../howto/annotations.rst:52
msgid ""
"However, other types of callables--for example, callables created by :func:"
"`functools.partial`--may not have an ``__annotations__`` attribute defined.  "
"When accessing the ``__annotations__`` of a possibly unknown object,  best "
"practice in Python versions 3.10 and newer is to call :func:`getattr` with "
"three arguments, for example ``getattr(o, '__annotations__', None)``."
msgstr ""

#: ../../howto/annotations.rst:60
msgid ""
"Before Python 3.10, accessing ``__annotations__`` on a class that defines no "
"annotations but that has a parent class with annotations would return the "
"parent's ``__annotations__``. In Python 3.10 and newer, the child class's "
"annotations will be an empty dict instead."
msgstr ""

#: ../../howto/annotations.rst:68
msgid "Accessing The Annotations Dict Of An Object In Python 3.9 And Older"
msgstr ""

#: ../../howto/annotations.rst:70
msgid ""
"In Python 3.9 and older, accessing the annotations dict of an object is much "
"more complicated than in newer versions. The problem is a design flaw in "
"these older versions of Python, specifically to do with class annotations."
msgstr ""

#: ../../howto/annotations.rst:75
msgid ""
"Best practice for accessing the annotations dict of other objects--"
"functions, other callables, and modules--is the same as best practice for "
"3.10, assuming you aren't calling :func:`inspect.get_annotations`: you "
"should use three-argument :func:`getattr` to access the object's "
"``__annotations__`` attribute."
msgstr ""

#: ../../howto/annotations.rst:82
msgid ""
"Unfortunately, this isn't best practice for classes.  The problem is that, "
"since ``__annotations__`` is optional on classes, and because classes can "
"inherit attributes from their base classes, accessing the "
"``__annotations__`` attribute of a class may inadvertently return the "
"annotations dict of a *base class.* As an example::"
msgstr ""

#: ../../howto/annotations.rst:89
msgid ""
"class Base:\n"
"    a: int = 3\n"
"    b: str = 'abc'\n"
"\n"
"class Derived(Base):\n"
"    pass\n"
"\n"
"print(Derived.__annotations__)"
msgstr ""

#: ../../howto/annotations.rst:98
msgid "This will print the annotations dict from ``Base``, not ``Derived``."
msgstr ""

#: ../../howto/annotations.rst:101
msgid ""
"Your code will have to have a separate code path if the object you're "
"examining is a class (``isinstance(o, type)``). In that case, best practice "
"relies on an implementation detail of Python 3.9 and before: if a class has "
"annotations defined, they are stored in the class's :attr:`~type.__dict__` "
"dictionary.  Since the class may or may not have annotations defined, best "
"practice is to call the :meth:`~dict.get` method on the class dict."
msgstr ""

#: ../../howto/annotations.rst:109
msgid ""
"To put it all together, here is some sample code that safely accesses the "
"``__annotations__`` attribute on an arbitrary object in Python 3.9 and "
"before::"
msgstr ""

#: ../../howto/annotations.rst:113
msgid ""
"if isinstance(o, type):\n"
"    ann = o.__dict__.get('__annotations__', None)\n"
"else:\n"
"    ann = getattr(o, '__annotations__', None)"
msgstr ""

#: ../../howto/annotations.rst:118
msgid ""
"After running this code, ``ann`` should be either a dictionary or ``None``.  "
"You're encouraged to double-check the type of ``ann`` using :func:"
"`isinstance` before further examination."
msgstr ""

#: ../../howto/annotations.rst:123
msgid ""
"Note that some exotic or malformed type objects may not have a :attr:`~type."
"__dict__` attribute, so for extra safety you may also wish to use :func:"
"`getattr` to access :attr:`!__dict__`."
msgstr ""

#: ../../howto/annotations.rst:129
msgid "Manually Un-Stringizing Stringized Annotations"
msgstr ""

#: ../../howto/annotations.rst:131
msgid ""
"In situations where some annotations may be \"stringized\", and you wish to "
"evaluate those strings to produce the Python values they represent, it "
"really is best to call :func:`inspect.get_annotations` to do this work for "
"you."
msgstr ""

#: ../../howto/annotations.rst:137
msgid ""
"If you're using Python 3.9 or older, or if for some reason you can't use :"
"func:`inspect.get_annotations`, you'll need to duplicate its logic.  You're "
"encouraged to examine the implementation of :func:`inspect.get_annotations` "
"in the current Python version and follow a similar approach."
msgstr ""

#: ../../howto/annotations.rst:143
msgid ""
"In a nutshell, if you wish to evaluate a stringized annotation on an "
"arbitrary object ``o``:"
msgstr ""

#: ../../howto/annotations.rst:146
msgid ""
"If ``o`` is a module, use ``o.__dict__`` as the ``globals`` when calling :"
"func:`eval`."
msgstr ""

#: ../../howto/annotations.rst:148
msgid ""
"If ``o`` is a class, use ``sys.modules[o.__module__].__dict__`` as the "
"``globals``, and ``dict(vars(o))`` as the ``locals``, when calling :func:"
"`eval`."
msgstr ""

#: ../../howto/annotations.rst:151
msgid ""
"If ``o`` is a wrapped callable using :func:`functools.update_wrapper`, :func:"
"`functools.wraps`, or :func:`functools.partial`, iteratively unwrap it by "
"accessing either ``o.__wrapped__`` or ``o.func`` as appropriate, until you "
"have found the root unwrapped function."
msgstr ""

#: ../../howto/annotations.rst:155
msgid ""
"If ``o`` is a callable (but not a class), use :attr:`o.__globals__ <function."
"__globals__>` as the globals when calling :func:`eval`."
msgstr ""

#: ../../howto/annotations.rst:159
msgid ""
"However, not all string values used as annotations can be successfully "
"turned into Python values by :func:`eval`. String values could theoretically "
"contain any valid string, and in practice there are valid use cases for type "
"hints that require annotating with string values that specifically *can't* "
"be evaluated.  For example:"
msgstr ""

#: ../../howto/annotations.rst:166
msgid ""
":pep:`604` union types using ``|``, before support for this was added to "
"Python 3.10."
msgstr ""

#: ../../howto/annotations.rst:168
msgid ""
"Definitions that aren't needed at runtime, only imported when :const:`typing."
"TYPE_CHECKING` is true."
msgstr ""

#: ../../howto/annotations.rst:171
msgid ""
"If :func:`eval` attempts to evaluate such values, it will fail and raise an "
"exception.  So, when designing a library API that works with annotations, "
"it's recommended to only attempt to evaluate string values when explicitly "
"requested to by the caller."
msgstr ""

#: ../../howto/annotations.rst:179
msgid "Best Practices For ``__annotations__`` In Any Python Version"
msgstr ""

#: ../../howto/annotations.rst:181
msgid ""
"You should avoid assigning to the ``__annotations__`` member of objects "
"directly.  Let Python manage setting ``__annotations__``."
msgstr ""

#: ../../howto/annotations.rst:184
msgid ""
"If you do assign directly to the ``__annotations__`` member of an object, "
"you should always set it to a ``dict`` object."
msgstr ""

#: ../../howto/annotations.rst:187
msgid ""
"If you directly access the ``__annotations__`` member of an object, you "
"should ensure that it's a dictionary before attempting to examine its "
"contents."
msgstr ""

#: ../../howto/annotations.rst:191
msgid "You should avoid modifying ``__annotations__`` dicts."
msgstr ""

#: ../../howto/annotations.rst:193
msgid ""
"You should avoid deleting the ``__annotations__`` attribute of an object."
msgstr ""

#: ../../howto/annotations.rst:198
msgid "``__annotations__`` Quirks"
msgstr ""

#: ../../howto/annotations.rst:200
msgid ""
"In all versions of Python 3, function objects lazy-create an annotations "
"dict if no annotations are defined on that object.  You can delete the "
"``__annotations__`` attribute using ``del fn.__annotations__``, but if you "
"then access ``fn.__annotations__`` the object will create a new empty dict "
"that it will store and return as its annotations.  Deleting the annotations "
"on a function before it has lazily created its annotations dict will throw "
"an ``AttributeError``; using ``del fn.__annotations__`` twice in a row is "
"guaranteed to always throw an ``AttributeError``."
msgstr ""

#: ../../howto/annotations.rst:210
msgid ""
"Everything in the above paragraph also applies to class and module objects "
"in Python 3.10 and newer."
msgstr ""

#: ../../howto/annotations.rst:213
msgid ""
"In all versions of Python 3, you can set ``__annotations__`` on a function "
"object to ``None``.  However, subsequently accessing the annotations on that "
"object using ``fn.__annotations__`` will lazy-create an empty dictionary as "
"per the first paragraph of this section.  This is *not* true of modules and "
"classes, in any Python version; those objects permit setting "
"``__annotations__`` to any Python value, and will retain whatever value is "
"set."
msgstr ""

#: ../../howto/annotations.rst:221
msgid ""
"If Python stringizes your annotations for you (using ``from __future__ "
"import annotations``), and you specify a string as an annotation, the string "
"will itself be quoted.  In effect the annotation is quoted *twice.*  For "
"example::"
msgstr ""

#: ../../howto/annotations.rst:227
msgid ""
"from __future__ import annotations\n"
"def foo(a: \"str\"): pass\n"
"\n"
"print(foo.__annotations__)"
msgstr ""

#: ../../howto/annotations.rst:232
msgid ""
"This prints ``{'a': \"'str'\"}``.  This shouldn't really be considered a "
"\"quirk\"; it's mentioned here simply because it might be surprising."
msgstr ""