Fixed #29478 -- Added support for mangled names to cached_property.
Co-Authored-By: Sergey Fedoseev <fedoseev.sergey@gmail.com>
This commit is contained in:
Thomas Grainger
Tim Graham
parent
80ba7a881f
commit
0607699902
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@ -3,6 +3,8 @@ import itertools
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import operator
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from functools import total_ordering, wraps
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from django.utils.version import PY36, get_docs_version
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# You can't trivially replace this with `functools.partial` because this binds
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# to classes and returns bound instances, whereas functools.partial (on
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@ -18,13 +20,54 @@ class cached_property:
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Decorator that converts a method with a single self argument into a
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property cached on the instance.
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Optional ``name`` argument allows you to make cached properties of other
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methods. (e.g. url = cached_property(get_absolute_url, name='url') )
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A cached property can be made out of an existing method:
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(e.g. ``url = cached_property(get_absolute_url)``).
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On Python < 3.6, the optional ``name`` argument must be provided, e.g.
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``url = cached_property(get_absolute_url, name='url')``.
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"""
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name = None
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@staticmethod
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def func(instance):
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raise TypeError(
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'Cannot use cached_property instance without calling '
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'__set_name__() on it.'
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)
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@staticmethod
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def _is_mangled(name):
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return name.startswith('__') and not name.endswith('__')
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def __init__(self, func, name=None):
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self.func = func
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if PY36:
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self.real_func = func
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else:
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func_name = func.__name__
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name = name or func_name
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if not (isinstance(name, str) and name.isidentifier()):
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raise ValueError(
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"%r can't be used as the name of a cached_property." % name,
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)
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if self._is_mangled(name):
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raise ValueError(
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'cached_property does not work with mangled methods on '
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'Python < 3.6 without the appropriate `name` argument. See '
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'https://docs.djangoproject.com/en/%s/ref/utils/'
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'#cached-property-mangled-name' % get_docs_version(),
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)
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self.name = name
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self.func = func
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self.__doc__ = getattr(func, '__doc__')
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self.name = name or func.__name__
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def __set_name__(self, owner, name):
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if self.name is None:
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self.name = name
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self.func = self.real_func
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elif name != self.name:
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raise TypeError(
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"Cannot assign the same cached_property to two different names "
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"(%r and %r)." % (self.name, name)
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)
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def __get__(self, instance, cls=None):
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"""
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@ -492,13 +492,19 @@ https://web.archive.org/web/20110718035220/http://diveintomark.org/archives/2004
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database by some other process in the brief interval between subsequent
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invocations of a method on the same instance.
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You can use the ``name`` argument to make cached properties of other
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methods. For example, if you had an expensive ``get_friends()`` method and
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wanted to allow calling it without retrieving the cached value, you could
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write::
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You can make cached properties of methods. For example, if you had an
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expensive ``get_friends()`` method and wanted to allow calling it without
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retrieving the cached value, you could write::
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friends = cached_property(get_friends, name='friends')
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You only need the ``name`` argument for Python < 3.6 support.
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.. versionchanged:: 2.2
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Older versions of Django require the ``name`` argument for all versions
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of Python.
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While ``person.get_friends()`` will recompute the friends on each call, the
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value of the cached property will persist until you delete it as described
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above::
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@ -510,8 +516,11 @@ https://web.archive.org/web/20110718035220/http://diveintomark.org/archives/2004
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.. warning::
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``cached_property`` doesn't work properly with a mangled__ name unless
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it's passed a ``name`` of the form ``_Class__attribute``::
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.. _cached-property-mangled-name:
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On Python < 3.6, ``cached_property`` doesn't work properly with a
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mangled__ name unless it's passed a ``name`` of the form
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``_Class__attribute``::
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__friends = cached_property(get_friends, name='_Person__friends')
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@ -351,6 +351,35 @@ To simplify a few parts of Django's database handling, `sqlparse
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<https://pypi.org/project/sqlparse/>`_ is now a required dependency. It's
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automatically installed along with Django.
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``cached_property`` aliases
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---------------------------
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In usage like::
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from django.utils.functional import cached_property
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class A:
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@cached_property
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def base(self):
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return ...
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alias = base
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``alias`` is not cached. Such usage now raises ``TypeError: Cannot assign the
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same cached_property to two different names ('base' and 'alias').`` on Python
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3.6 and later.
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Use this instead::
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import operator
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class A:
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...
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alias = property(operator.attrgetter('base'))
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Miscellaneous
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-------------
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@ -1,9 +1,11 @@
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import unittest
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from django.test import SimpleTestCase
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from django.utils.functional import cached_property, lazy
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from django.utils.version import PY36
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class FunctionalTestCase(unittest.TestCase):
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class FunctionalTests(SimpleTestCase):
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def test_lazy(self):
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t = lazy(lambda: tuple(range(3)), list, tuple)
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for a, b in zip(t(), range(3)):
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@ -47,43 +49,168 @@ class FunctionalTestCase(unittest.TestCase):
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self.assertEqual(str(t), "Î am ā Ǩlâzz.")
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self.assertEqual(bytes(t), b"\xc3\x8e am \xc4\x81 binary \xc7\xa8l\xc3\xa2zz.")
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def test_cached_property(self):
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"""
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cached_property caches its value and that it behaves like a property
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"""
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class A:
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def assertCachedPropertyWorks(self, attr, Class):
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with self.subTest(attr=attr):
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def get(source):
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return getattr(source, attr)
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obj = Class()
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class SubClass(Class):
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pass
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subobj = SubClass()
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# Docstring is preserved.
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self.assertEqual(get(Class).__doc__, 'Here is the docstring...')
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self.assertEqual(get(SubClass).__doc__, 'Here is the docstring...')
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# It's cached.
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self.assertEqual(get(obj), get(obj))
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self.assertEqual(get(subobj), get(subobj))
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# The correct value is returned.
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self.assertEqual(get(obj)[0], 1)
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self.assertEqual(get(subobj)[0], 1)
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# State isn't shared between instances.
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obj2 = Class()
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subobj2 = SubClass()
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self.assertNotEqual(get(obj), get(obj2))
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self.assertNotEqual(get(subobj), get(subobj2))
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# It behaves like a property when there's no instance.
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self.assertIsInstance(get(Class), cached_property)
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self.assertIsInstance(get(SubClass), cached_property)
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# 'other_value' doesn't become a property.
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self.assertTrue(callable(obj.other_value))
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self.assertTrue(callable(subobj.other_value))
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def test_cached_property(self):
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"""cached_property caches its value and behaves like a property."""
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class Class:
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@cached_property
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def value(self):
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"""Here is the docstring..."""
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return 1, object()
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@cached_property
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def __foo__(self):
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"""Here is the docstring..."""
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return 1, object()
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def other_value(self):
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return 1
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"""Here is the docstring..."""
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return 1, object()
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other = cached_property(other_value, name='other')
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# docstring should be preserved
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self.assertEqual(A.value.__doc__, "Here is the docstring...")
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attrs = ['value', 'other', '__foo__']
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for attr in attrs:
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self.assertCachedPropertyWorks(attr, Class)
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@unittest.skipUnless(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_auto_name(self):
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"""
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cached_property caches its value and behaves like a property
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on mangled methods or when the name kwarg isn't set.
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"""
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class Class:
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@cached_property
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def __value(self):
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"""Here is the docstring..."""
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return 1, object()
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def other_value(self):
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"""Here is the docstring..."""
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return 1, object()
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other = cached_property(other_value)
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other2 = cached_property(other_value, name='different_name')
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attrs = ['_Class__value', 'other']
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for attr in attrs:
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self.assertCachedPropertyWorks(attr, Class)
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# An explicit name is ignored.
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obj = Class()
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obj.other2
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self.assertFalse(hasattr(obj, 'different_name'))
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@unittest.skipUnless(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_reuse_different_names(self):
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"""Disallow this case because the decorated function wouldn't be cached."""
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with self.assertRaises(RuntimeError) as ctx:
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class ReusedCachedProperty:
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@cached_property
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def a(self):
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pass
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b = a
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self.assertEqual(
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str(ctx.exception.__context__),
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str(TypeError(
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"Cannot assign the same cached_property to two different "
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"names ('a' and 'b')."
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))
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)
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@unittest.skipUnless(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_reuse_same_name(self):
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"""
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Reusing a cached_property on different classes under the same name is
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allowed.
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"""
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counter = 0
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@cached_property
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def _cp(_self):
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nonlocal counter
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counter += 1
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return counter
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class A:
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cp = _cp
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class B:
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cp = _cp
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a = A()
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b = B()
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self.assertEqual(a.cp, 1)
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self.assertEqual(b.cp, 2)
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self.assertEqual(a.cp, 1)
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# check that it is cached
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self.assertEqual(a.value, a.value)
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@unittest.skipUnless(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_set_name_not_called(self):
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cp = cached_property(lambda s: None)
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# check that it returns the right thing
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self.assertEqual(a.value[0], 1)
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class Foo:
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pass
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# check that state isn't shared between instances
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a2 = A()
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self.assertNotEqual(a.value, a2.value)
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Foo.cp = cp
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msg = 'Cannot use cached_property instance without calling __set_name__() on it.'
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with self.assertRaisesMessage(TypeError, msg):
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Foo().cp
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# check that it behaves like a property when there's no instance
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self.assertIsInstance(A.value, cached_property)
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@unittest.skipIf(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_mangled_error(self):
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msg = (
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'cached_property does not work with mangled methods on '
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'Python < 3.6 without the appropriate `name` argument.'
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)
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with self.assertRaisesMessage(ValueError, msg):
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@cached_property
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def __value(self):
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pass
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with self.assertRaisesMessage(ValueError, msg):
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def func(self):
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pass
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cached_property(func, name='__value')
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# check that overriding name works
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self.assertEqual(a.other, 1)
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self.assertTrue(callable(a.other_value))
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@unittest.skipIf(PY36, '__set_name__ is new in Python 3.6')
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def test_cached_property_name_validation(self):
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msg = "%s can't be used as the name of a cached_property."
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with self.assertRaisesMessage(ValueError, msg % "'<lambda>'"):
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cached_property(lambda x: None)
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with self.assertRaisesMessage(ValueError, msg % 42):
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cached_property(str, name=42)
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def test_lazy_equality(self):
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"""
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