django/tests/utils_tests/test_functional.py

from unittest import mock

from django.test import SimpleTestCase
from django.utils.functional import cached_property, lazy


class FunctionalTests(SimpleTestCase):
    def test_lazy(self):
        t = lazy(lambda: tuple(range(3)), list, tuple)
        for a, b in zip(t(), range(3)):
            self.assertEqual(a, b)

    def test_lazy_base_class(self):
        """lazy also finds base class methods in the proxy object"""
        class Base:
            def base_method(self):
                pass

        class Klazz(Base):
            pass

        t = lazy(lambda: Klazz(), Klazz)()
        self.assertIn('base_method', dir(t))

    def test_lazy_base_class_override(self):
        """lazy finds the correct (overridden) method implementation"""
        class Base:
            def method(self):
                return 'Base'

        class Klazz(Base):
            def method(self):
                return 'Klazz'

        t = lazy(lambda: Klazz(), Base)()
        self.assertEqual(t.method(), 'Klazz')

    def test_lazy_object_to_string(self):

        class Klazz:
            def __str__(self):
                return "Î am ā Ǩlâzz."

            def __bytes__(self):
                return b"\xc3\x8e am \xc4\x81 binary \xc7\xa8l\xc3\xa2zz."

        t = lazy(lambda: Klazz(), Klazz)()
        self.assertEqual(str(t), "Î am ā Ǩlâzz.")
        self.assertEqual(bytes(t), b"\xc3\x8e am \xc4\x81 binary \xc7\xa8l\xc3\xa2zz.")

    def assertCachedPropertyWorks(self, attr, Class):
        with self.subTest(attr=attr):
            def get(source):
                return getattr(source, attr)

            obj = Class()

            class SubClass(Class):
                pass

            subobj = SubClass()
            # Docstring is preserved.
            self.assertEqual(get(Class).__doc__, 'Here is the docstring...')
            self.assertEqual(get(SubClass).__doc__, 'Here is the docstring...')
            # It's cached.
            self.assertEqual(get(obj), get(obj))
            self.assertEqual(get(subobj), get(subobj))
            # The correct value is returned.
            self.assertEqual(get(obj)[0], 1)
            self.assertEqual(get(subobj)[0], 1)
            # State isn't shared between instances.
            obj2 = Class()
            subobj2 = SubClass()
            self.assertNotEqual(get(obj), get(obj2))
            self.assertNotEqual(get(subobj), get(subobj2))
            # It behaves like a property when there's no instance.
            self.assertIsInstance(get(Class), cached_property)
            self.assertIsInstance(get(SubClass), cached_property)
            # 'other_value' doesn't become a property.
            self.assertTrue(callable(obj.other_value))
            self.assertTrue(callable(subobj.other_value))

    def test_cached_property(self):
        """cached_property caches its value and behaves like a property."""
        class Class:
            @cached_property
            def value(self):
                """Here is the docstring..."""
                return 1, object()

            @cached_property
            def __foo__(self):
                """Here is the docstring..."""
                return 1, object()

            def other_value(self):
                """Here is the docstring..."""
                return 1, object()

            other = cached_property(other_value, name='other')

        attrs = ['value', 'other', '__foo__']
        for attr in attrs:
            self.assertCachedPropertyWorks(attr, Class)

    def test_cached_property_auto_name(self):
        """
        cached_property caches its value and behaves like a property
        on mangled methods or when the name kwarg isn't set.
        """
        class Class:
            @cached_property
            def __value(self):
                """Here is the docstring..."""
                return 1, object()

            def other_value(self):
                """Here is the docstring..."""
                return 1, object()

            other = cached_property(other_value)
            other2 = cached_property(other_value, name='different_name')

        attrs = ['_Class__value', 'other']
        for attr in attrs:
            self.assertCachedPropertyWorks(attr, Class)

        # An explicit name is ignored.
        obj = Class()
        obj.other2
        self.assertFalse(hasattr(obj, 'different_name'))

    def test_cached_property_reuse_different_names(self):
        """Disallow this case because the decorated function wouldn't be cached."""
        with self.assertRaises(RuntimeError) as ctx:
            class ReusedCachedProperty:
                @cached_property
                def a(self):
                    pass

                b = a

        self.assertEqual(
            str(ctx.exception.__context__),
            str(TypeError(
                "Cannot assign the same cached_property to two different "
                "names ('a' and 'b')."
            ))
        )

    def test_cached_property_reuse_same_name(self):
        """
        Reusing a cached_property on different classes under the same name is
        allowed.
        """
        counter = 0

        @cached_property
        def _cp(_self):
            nonlocal counter
            counter += 1
            return counter

        class A:
            cp = _cp

        class B:
            cp = _cp

        a = A()
        b = B()
        self.assertEqual(a.cp, 1)
        self.assertEqual(b.cp, 2)
        self.assertEqual(a.cp, 1)

    def test_cached_property_set_name_not_called(self):
        cp = cached_property(lambda s: None)

        class Foo:
            pass

        Foo.cp = cp
        msg = 'Cannot use cached_property instance without calling __set_name__() on it.'
        with self.assertRaisesMessage(TypeError, msg):
            Foo().cp

    def test_lazy_equality(self):
        """
        == and != work correctly for Promises.
        """
        lazy_a = lazy(lambda: 4, int)
        lazy_b = lazy(lambda: 4, int)
        lazy_c = lazy(lambda: 5, int)

        self.assertEqual(lazy_a(), lazy_b())
        self.assertNotEqual(lazy_b(), lazy_c())

    def test_lazy_repr_text(self):
        original_object = 'Lazy translation text'
        lazy_obj = lazy(lambda: original_object, str)
        self.assertEqual(repr(original_object), repr(lazy_obj()))

    def test_lazy_repr_int(self):
        original_object = 15
        lazy_obj = lazy(lambda: original_object, int)
        self.assertEqual(repr(original_object), repr(lazy_obj()))

    def test_lazy_repr_bytes(self):
        original_object = b'J\xc3\xbcst a str\xc3\xadng'
        lazy_obj = lazy(lambda: original_object, bytes)
        self.assertEqual(repr(original_object), repr(lazy_obj()))

    def test_lazy_class_preparation_caching(self):
        # lazy() should prepare the proxy class only once i.e. the first time
        # it's used.
        lazified = lazy(lambda: 0, int)
        __proxy__ = lazified().__class__
        with mock.patch.object(__proxy__, '__prepare_class__') as mocked:
            lazified()
            mocked.assert_not_called()