8000 [3.7] bpo-37479: on Enum subclasses with mixins, __format__ uses over… · ethanfurman/cpython@03c803b · GitHub
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[3.7] bpo-37479: on Enum subclasses with mixins, __format__ uses overridden __str__ (pythonGH-14545)
* bpo-37479: on Enum subclasses with mixins, __format__ uses overridden __str__. (cherry picked from commit 2f19e82) Co-authored-by: thatneat <thatneat@users.noreply.github.com>
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  • Doc/library
  • Lib
  • Misc
    • ACKS
    • NEWS.d/next/Library
      • 2019-07-02-12-43-57.bpo-37479.O53a5S.rst

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‎Doc/library/enum.rst

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@@ -743,9 +743,11 @@ Some rules:
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:meth:`__str__` and :meth:`__repr__` respectively; other codes (such as
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`%i` or `%h` for IntEnum) treat the enum member as its mixed-in type.
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5. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`,
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and :func:`format` will use the mixed-in
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type's :meth:`__format__`. If the :class:`Enum` class's :func:`str` or
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:func:`repr` is desired, use the `!s` or `!r` format codes.
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and :func:`format` will use the mixed-in type's :meth:`__format__`
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unless :meth:`__str__` or :meth:`__format__` is overridden in the subclass,
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in which case the overridden methods or :class:`Enum` methods will be used.
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Use the !s and !r format codes to force usage of the :class:`Enum` class's
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:meth:`__str__` and :meth:`__repr__` methods.
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Interesting examples

‎Lib/enum.py

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@@ -602,8 +602,9 @@ def __format__(self, format_spec):
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# we can get strange results with the Enum name showing up instead of
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# the value
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# pure Enum branch
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if self._member_type_ is object:
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# pure Enum branch, or branch with __str__ explicitly overridden
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str_overridden = type(self).__str__ != Enum.__str__
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if self._member_type_ is object or str_overridden:
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cls = str
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val = str(self)
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# mix-in branch

‎Lib/test/test_enum.py

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@@ -453,12 +453,63 @@ def test_format_enum(self):
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self.assertEqual('{:<20}'.format(Season.SPRING),
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'{:<20}'.format(str(Season.SPRING)))
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def test_format_enum_custom(self):
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def test_str_override_enum(self):
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class EnumWithStrOverrides(Enum):
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one = auto()
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two = auto()
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def __str__(self):
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return 'Str!'
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self.assertEqual(str(EnumWithStrOverrides.one), 'Str!')
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self.assertEqual('{}'.format(EnumWithStrOverrides.one), 'Str!')
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def test_format_override_enum(self):
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class EnumWithFormatOverride(Enum):
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one = 1.0
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two = 2.0
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def __format__(self, spec):
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return 'Format!!'
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self.assertEqual(str(EnumWithFormatOverride.one), 'EnumWithFormatOverride.one')
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self.assertEqual('{}'.format(EnumWithFormatOverride.one), 'Format!!')
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def test_str_and_format_override_enum(self):
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class EnumWithStrFormatOverrides(Enum):
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one = auto()
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two = auto()
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def __str__(self):
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return 'Str!'
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def __format__(self, spec):
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return 'Format!'
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self.assertEqual(str(EnumWithStrFormatOverrides.one), 'Str!')
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self.assertEqual('{}'.format(EnumWithStrFormatOverrides.one), 'Format!')
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def test_str_override_mixin(self):
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class MixinEnumWithStrOverride(float, Enum):
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one = 1.0
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two = 2.0
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def __str__(self):
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return 'Overridden!'
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self.assertEqual(str(MixinEnumWithStrOverride.one), 'Overridden!')
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self.assertEqual('{}'.format(MixinEnumWithStrOverride.one), 'Overridden!')
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def test_str_and_format_override_mixin(self):
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class MixinWithStrFormatOverrides(float, Enum):
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one = 1.0
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two = 2.0
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def __str__(self):
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return 'Str!'
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def __format__(self, spec):
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return 'Format!'
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self.assertEqual(str(MixinWithStrFormatOverrides.one), 'Str!')
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self.assertEqual('{}'.format(MixinWithStrFormatOverrides.one), 'Format!')
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def test_format_override_mixin(self):
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class TestFloat(float, Enum):
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one = 1.0
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two = 2.0
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def __format__(self, spec):
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return 'TestFloat success!'
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self.assertEqual(str(TestFloat.one), 'TestFloat.one')
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self.assertEqual('{}'.format(TestFloat.one), 'TestFloat success!')
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def assertFormatIsValue(self, spec, member):

‎Misc/ACKS

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@@ -356,6 +356,8 @@ Tom Culliton
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Raúl Cumplido
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Antonio Cuni
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Brian Curtin
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Jason Curtis
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Paul Dagnelie
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Lisandro Dalcin
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Darren Dale
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Andrew Dalke

‎Misc/NEWS.d/next/Library/2019-07-02-12-43-57.bpo-37479.O53a5S.rst

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@@ -0,0 +1,2 @@
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When `Enum.__str__` is overridden in a derived class, the override will be
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used by `Enum.__format__` regardless of whether mixin classes are present.

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