bpo-40066: [Enum] update str() and format() output (GH-30582)

Undo rejected PEP-663 changes:

- restore `repr()` to its 3.10 status
- restore `str()` to its 3.10 status

New changes:

- `IntEnum` and `IntFlag` now leave `__str__` as the original `int.__str__` so that str() and format() return the same result
- zero-valued flags without a name have a slightly changed repr(), e.g. `repr(Color(0)) == '<Color: 0>'`
- update `dir()` for mixed-in types to return all the methods and attributes of the mixed-in type
- added `_numeric_repr_` to `Flag` to control display of unnamed values
- enums without doc strings have a more comprehensive doc string added
- `ReprEnum` added -- inheriting from this makes it so only `__repr__` is replaced, not `__str__` nor `__format__`; `IntEnum`, `IntFlag`, and `StrEnum` all inherit from `ReprEnum`
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@ -2,15 +2,10 @@
Enum HOWTO
==========
:Author: Ethan Furman <ethan at stoneleaf dot us>
.. _enum-basic-tutorial:
.. currentmodule:: enum
Basic Enum Tutorial
-------------------
An :class:`Enum` is a set of symbolic names bound to unique values. They are
similar to global variables, but they offer a more useful :func:`repr()`,
grouping, type-safety, and a few other features.
@ -28,6 +23,14 @@ selection of values. For example, the days of the week::
... SATURDAY = 6
... SUNDAY = 7
Or perhaps the RGB primary colors::
>>> from enum import Enum
>>> class Color(Enum):
... RED = 1
... GREEN = 2
... BLUE = 3
As you can see, creating an :class:`Enum` is as simple as writing a class that
inherits from :class:`Enum` itself.
@ -41,13 +44,14 @@ important, but either way that value can be used to get the corresponding
member::
>>> Weekday(3)
Weekday.WEDNESDAY
<Weekday.WEDNESDAY: 3>
As you can see, the ``repr()`` of a member shows the enum name and the
member name. The ``str()`` on a member shows only its name::
As you can see, the ``repr()`` of a member shows the enum name, the member name,
and the value. The ``str()`` of a member shows only the enum name and member
name::
>>> print(Weekday.THURSDAY)
THURSDAY
Weekday.THURSDAY
The *type* of an enumeration member is the enum it belongs to::
@ -97,8 +101,8 @@ The complete :class:`Weekday` enum now looks like this::
Now we can find out what today is! Observe::
>>> from datetime import date
>>> Weekday.from_date(date.today())
Weekday.TUESDAY
>>> Weekday.from_date(date.today()) # doctest: +SKIP
<Weekday.TUESDAY: 2>
Of course, if you're reading this on some other day, you'll see that day instead.
@ -124,21 +128,21 @@ Just like the original :class:`Weekday` enum above, we can have a single selecti
>>> first_week_day = Weekday.MONDAY
>>> first_week_day
Weekday.MONDAY
<Weekday.MONDAY: 1>
But :class:`Flag` also allows us to combine several members into a single
variable::
>>> weekend = Weekday.SATURDAY | Weekday.SUNDAY
>>> weekend
Weekday.SATURDAY|Weekday.SUNDAY
<Weekday.SATURDAY|SUNDAY: 96>
You can even iterate over a :class:`Flag` variable::
>>> for day in weekend:
... print(day)
SATURDAY
SUNDAY
Weekday.SATURDAY
Weekday.SUNDAY
Okay, let's get some chores set up::
@ -173,6 +177,7 @@ yourself some work and use :func:`auto()` for the values::
.. _enum-advanced-tutorial:
Programmatic access to enumeration members and their attributes
---------------------------------------------------------------
@ -181,16 +186,16 @@ situations where ``Color.RED`` won't do because the exact color is not known
at program-writing time). ``Enum`` allows such access::
>>> Color(1)
Color.RED
<Color.RED: 1>
>>> Color(3)
Color.BLUE
<Color.BLUE: 3>
If you want to access enum members by *name*, use item access::
>>> Color['RED']
Color.RED
<Color.RED: 1>
>>> Color['GREEN']
Color.GREEN
<Color.GREEN: 2>
If you have an enum member and need its :attr:`name` or :attr:`value`::
@ -212,7 +217,7 @@ Having two enum members with the same name is invalid::
...
Traceback (most recent call last):
...
TypeError: 'SQUARE' already defined as: 2
TypeError: 'SQUARE' already defined as 2
However, an enum member can have other names associated with it. Given two
entries ``A`` and ``B`` with the same value (and ``A`` defined first), ``B``
@ -227,11 +232,11 @@ By-name lookup of ``B`` will also return the member ``A``::
... ALIAS_FOR_SQUARE = 2
...
>>> Shape.SQUARE
Shape.SQUARE
<Shape.SQUARE: 2>
>>> Shape.ALIAS_FOR_SQUARE
Shape.SQUARE
<Shape.SQUARE: 2>
>>> Shape(2)
Shape.SQUARE
<Shape.SQUARE: 2>
.. note::
@ -299,7 +304,7 @@ Iteration
Iterating over the members of an enum does not provide the aliases::
>>> list(Shape)
[Shape.SQUARE, Shape.DIAMOND, Shape.CIRCLE]
[<Shape.SQUARE: 2>, <Shape.DIAMOND: 1>, <Shape.CIRCLE: 3>]
The special attribute ``__members__`` is a read-only ordered mapping of names
to members. It includes all names defined in the enumeration, including the
@ -308,10 +313,10 @@ aliases::
>>> for name, member in Shape.__members__.items():
... name, member
...
('SQUARE', Shape.SQUARE)
('DIAMOND', Shape.DIAMOND)
('CIRCLE', Shape.CIRCLE)
('ALIAS_FOR_SQUARE', Shape.SQUARE)
('SQUARE', <Shape.SQUARE: 2>)
('DIAMOND', <Shape.DIAMOND: 1>)
('CIRCLE', <Shape.CIRCLE: 3>)
('ALIAS_FOR_SQUARE', <Shape.SQUARE: 2>)
The ``__members__`` attribute can be used for detailed programmatic access to
the enumeration members. For example, finding all the aliases::
@ -360,8 +365,8 @@ below)::
Allowed members and attributes of enumerations
----------------------------------------------
Most of the examples above use integers for enumeration values. Using integers is
short and handy (and provided by default by the `Functional API`_), but not
Most of the examples above use integers for enumeration values. Using integers
is short and handy (and provided by default by the `Functional API`_), but not
strictly enforced. In the vast majority of use-cases, one doesn't care what
the actual value of an enumeration is. But if the value *is* important,
enumerations can have arbitrary values.
@ -389,7 +394,7 @@ usual. If we have this enumeration::
Then::
>>> Mood.favorite_mood()
Mood.HAPPY
<Mood.HAPPY: 3>
>>> Mood.HAPPY.describe()
('HAPPY', 3)
>>> str(Mood.FUNKY)
@ -425,7 +430,7 @@ any members. So this is forbidden::
...
Traceback (most recent call last):
...
TypeError: MoreColor: cannot extend enumeration 'Color'
TypeError: <enum 'MoreColor'> cannot extend <enum 'Color'>
But this is allowed::
@ -476,11 +481,9 @@ The :class:`Enum` class is callable, providing the following functional API::
>>> Animal
<enum 'Animal'>
>>> Animal.ANT
Animal.ANT
>>> Animal.ANT.value
1
<Animal.ANT: 1>
>>> list(Animal)
[Animal.ANT, Animal.BEE, Animal.CAT, Animal.DOG]
[<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]
The semantics of this API resemble :class:`~collections.namedtuple`. The first
argument of the call to :class:`Enum` is the name of the enumeration.
@ -625,16 +628,7 @@ StrEnum
The second variation of :class:`Enum` that is provided is also a subclass of
:class:`str`. Members of a :class:`StrEnum` can be compared to strings;
by extension, string enumerations of different types can also be compared
to each other. :class:`StrEnum` exists to help avoid the problem of getting
an incorrect member::
>>> from enum import StrEnum
>>> class Directions(StrEnum):
... NORTH = 'north', # notice the trailing comma
... SOUTH = 'south'
Before :class:`StrEnum`, ``Directions.NORTH`` would have been the :class:`tuple`
``('north',)``.
to each other.
.. versionadded:: 3.11
@ -645,9 +639,8 @@ IntFlag
The next variation of :class:`Enum` provided, :class:`IntFlag`, is also based
on :class:`int`. The difference being :class:`IntFlag` members can be combined
using the bitwise operators (&, \|, ^, ~) and the result is still an
:class:`IntFlag` member, if possible. However, as the name implies, :class:`IntFlag`
members also subclass :class:`int` and can be used wherever an :class:`int` is
used.
:class:`IntFlag` member, if possible. Like :class:`IntEnum`, :class:`IntFlag`
members are also integers and can be used wherever an :class:`int` is used.
.. note::
@ -670,7 +663,7 @@ Sample :class:`IntFlag` class::
... X = 1
...
>>> Perm.R | Perm.W
Perm.R|Perm.W
<Perm.R|W: 6>
>>> Perm.R + Perm.W
6
>>> RW = Perm.R | Perm.W
@ -685,11 +678,11 @@ It is also possible to name the combinations::
... X = 1
... RWX = 7
>>> Perm.RWX
Perm.RWX
<Perm.RWX: 7>
>>> ~Perm.RWX
Perm(0)
<Perm: 0>
>>> Perm(7)
Perm.RWX
<Perm.RWX: 7>
.. note::
@ -702,7 +695,7 @@ Another important difference between :class:`IntFlag` and :class:`Enum` is that
if no flags are set (the value is 0), its boolean evaluation is :data:`False`::
>>> Perm.R & Perm.X
Perm(0)
<Perm: 0>
>>> bool(Perm.R & Perm.X)
False
@ -710,7 +703,7 @@ Because :class:`IntFlag` members are also subclasses of :class:`int` they can
be combined with them (but may lose :class:`IntFlag` membership::
>>> Perm.X | 4
Perm.R|Perm.X
<Perm.R|X: 5>
>>> Perm.X | 8
9
@ -726,7 +719,7 @@ be combined with them (but may lose :class:`IntFlag` membership::
:class:`IntFlag` members can also be iterated over::
>>> list(RW)
[Perm.R, Perm.W]
[<Perm.R: 4>, <Perm.W: 2>]
.. versionadded:: 3.11
@ -753,7 +746,7 @@ flags being set, the boolean evaluation is :data:`False`::
... GREEN = auto()
...
>>> Color.RED & Color.GREEN
Color(0)
<Color: 0>
>>> bool(Color.RED & Color.GREEN)
False
@ -767,7 +760,7 @@ while combinations of flags won't::
... WHITE = RED | BLUE | GREEN
...
>>> Color.WHITE
Color.WHITE
<Color.WHITE: 7>
Giving a name to the "no flags set" condition does not change its boolean
value::
@ -779,7 +772,7 @@ value::
... GREEN = auto()
...
>>> Color.BLACK
Color.BLACK
<Color.BLACK: 0>
>>> bool(Color.BLACK)
False
@ -787,7 +780,7 @@ value::
>>> purple = Color.RED | Color.BLUE
>>> list(purple)
[Color.RED, Color.BLUE]
[<Color.RED: 1>, <Color.BLUE: 2>]
.. versionadded:: 3.11
@ -812,16 +805,16 @@ simple to implement independently::
pass
This demonstrates how similar derived enumerations can be defined; for example
a :class:`StrEnum` that mixes in :class:`str` instead of :class:`int`.
a :class:`FloatEnum` that mixes in :class:`float` instead of :class:`int`.
Some rules:
1. When subclassing :class:`Enum`, mix-in types must appear before
:class:`Enum` itself in the sequence of bases, as in the :class:`IntEnum`
example above.
2. Mix-in types must be subclassable. For example,
:class:`bool` and :class:`range` are not subclassable
and will throw an error during Enum creation if used as the mix-in type.
2. Mix-in types must be subclassable. For example, :class:`bool` and
:class:`range` are not subclassable and will throw an error during Enum
creation if used as the mix-in type.
3. While :class:`Enum` can have members of any type, once you mix in an
additional type, all the members must have values of that type, e.g.
:class:`int` above. This restriction does not apply to mix-ins which only
@ -829,15 +822,18 @@ Some rules:
4. When another data type is mixed in, the :attr:`value` attribute is *not the
same* as the enum member itself, although it is equivalent and will compare
equal.
5. %-style formatting: `%s` and `%r` call the :class:`Enum` class's
5. %-style formatting: ``%s`` and ``%r`` call the :class:`Enum` class's
:meth:`__str__` and :meth:`__repr__` respectively; other codes (such as
`%i` or `%h` for IntEnum) treat the enum member as its mixed-in type.
``%i`` or ``%h`` for IntEnum) treat the enum member as its mixed-in type.
6. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`,
and :func:`format` will use the mixed-in type's :meth:`__format__`
unless :meth:`__str__` or :meth:`__format__` is overridden in the subclass,
in which case the overridden methods or :class:`Enum` methods will be used.
Use the !s and !r format codes to force usage of the :class:`Enum` class's
:meth:`__str__` and :meth:`__repr__` methods.
and :func:`format` will use the enum's :meth:`__str__` method.
.. note::
Because :class:`IntEnum`, :class:`IntFlag`, and :class:`StrEnum` are
designed to be drop-in replacements for existing constants, their
:meth:`__str__` method has been reset to their data types
:meth:`__str__` method.
When to use :meth:`__new__` vs. :meth:`__init__`
------------------------------------------------
@ -866,10 +862,10 @@ want one of them to be the value::
...
>>> print(Coordinate['PY'])
PY
Coordinate.PY
>>> print(Coordinate(3))
VY
Coordinate.VY
Finer Points
@ -927,8 +923,8 @@ and raise an error if the two do not match::
Traceback (most recent call last):
...
TypeError: member order does not match _order_:
['RED', 'BLUE', 'GREEN']
['RED', 'GREEN', 'BLUE']
['RED', 'BLUE', 'GREEN']
['RED', 'GREEN', 'BLUE']
.. note::
@ -949,35 +945,36 @@ but remain normal attributes.
""""""""""""""""""""
Enum members are instances of their enum class, and are normally accessed as
``EnumClass.member``. In Python versions ``3.5`` to ``3.9`` you could access
members from other members -- this practice was discouraged, and in ``3.12``
:class:`Enum` will return to not allowing it, while in ``3.10`` and ``3.11``
it will raise a :exc:`DeprecationWarning`::
``EnumClass.member``. In Python versions ``3.5`` to ``3.10`` you could access
members from other members -- this practice was discouraged, and in ``3.11``
:class:`Enum` returns to not allowing it::
>>> class FieldTypes(Enum):
... name = 0
... value = 1
... size = 2
...
>>> FieldTypes.value.size # doctest: +SKIP
DeprecationWarning: accessing one member from another is not supported,
and will be disabled in 3.12
<FieldTypes.size: 2>
>>> FieldTypes.value.size
Traceback (most recent call last):
...
AttributeError: <enum 'FieldTypes'> member has no attribute 'size'
.. versionchanged:: 3.5
.. versionchanged:: 3.11
Creating members that are mixed with other data types
"""""""""""""""""""""""""""""""""""""""""""""""""""""
When subclassing other data types, such as :class:`int` or :class:`str`, with
an :class:`Enum`, all values after the `=` are passed to that data type's
an :class:`Enum`, all values after the ``=`` are passed to that data type's
constructor. For example::
>>> class MyEnum(IntEnum):
... example = '11', 16 # '11' will be interpreted as a hexadecimal
... # number
>>> MyEnum.example.value
>>> class MyEnum(IntEnum): # help(int) -> int(x, base=10) -> integer
... example = '11', 16 # so x='11' and base=16
...
>>> MyEnum.example.value # and hex(11) is...
17
@ -1000,13 +997,12 @@ Plain :class:`Enum` classes always evaluate as :data:`True`.
"""""""""""""""""""""""""""""
If you give your enum subclass extra methods, like the `Planet`_
class below, those methods will show up in a :func:`dir` of the member and the
class. Attributes defined in an :func:`__init__` method will only show up in a
:func:`dir` of the member::
class below, those methods will show up in a :func:`dir` of the member,
but not of the class::
>>> dir(Planet)
['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS', 'VENUS', '__class__', '__doc__', '__init__', '__members__', '__module__', 'surface_gravity']
>>> dir(Planet.EARTH)
>>> dir(Planet) # doctest: +SKIP
['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS', 'VENUS', '__class__', '__doc__', '__members__', '__module__']
>>> dir(Planet.EARTH) # doctest: +SKIP
['__class__', '__doc__', '__module__', 'mass', 'name', 'radius', 'surface_gravity', 'value']
@ -1025,19 +1021,10 @@ are comprised of a single bit::
... CYAN = GREEN | BLUE
...
>>> Color(3) # named combination
Color.YELLOW
<Color.YELLOW: 3>
>>> Color(7) # not named combination
Color.RED|Color.GREEN|Color.BLUE
<Color.RED|GREEN|BLUE: 7>
``StrEnum`` and :meth:`str.__str__`
"""""""""""""""""""""""""""""""""""
An important difference between :class:`StrEnum` and other Enums is the
:meth:`__str__` method; because :class:`StrEnum` members are strings, some
parts of Python will read the string data directly, while others will call
:meth:`str()`. To make those two operations have the same result,
:meth:`StrEnum.__str__` will be the same as :meth:`str.__str__` so that
``str(StrEnum.member) == StrEnum.member`` is true.
``Flag`` and ``IntFlag`` minutia
""""""""""""""""""""""""""""""""
@ -1060,16 +1047,16 @@ the following are true:
- only canonical flags are returned during iteration::
>>> list(Color.WHITE)
[Color.RED, Color.GREEN, Color.BLUE]
[<Color.RED: 1>, <Color.GREEN: 2>, <Color.BLUE: 4>]
- negating a flag or flag set returns a new flag/flag set with the
corresponding positive integer value::
>>> Color.BLUE
Color.BLUE
<Color.BLUE: 4>
>>> ~Color.BLUE
Color.RED|Color.GREEN
<Color.RED|GREEN: 3>
- names of pseudo-flags are constructed from their members' names::
@ -1079,25 +1066,29 @@ the following are true:
- multi-bit flags, aka aliases, can be returned from operations::
>>> Color.RED | Color.BLUE
Color.PURPLE
<Color.PURPLE: 5>
>>> Color(7) # or Color(-1)
Color.WHITE
<Color.WHITE: 7>
>>> Color(0)
Color.BLACK
<Color.BLACK: 0>
- membership / containment checking has changed slightly -- zero-valued flags
are never considered to be contained::
- membership / containment checking: zero-valued flags are always considered
to be contained::
>>> Color.BLACK in Color.WHITE
False
True
otherwise, if all bits of one flag are in the other flag, True is returned::
otherwise, only if all bits of one flag are in the other flag will True
be returned::
>>> Color.PURPLE in Color.WHITE
True
>>> Color.GREEN in Color.PURPLE
False
There is a new boundary mechanism that controls how out-of-range / invalid
bits are handled: ``STRICT``, ``CONFORM``, ``EJECT``, and ``KEEP``:
@ -1181,7 +1172,7 @@ Using :class:`auto` would look like::
... GREEN = auto()
...
>>> Color.GREEN
<Color.GREEN>
<Color.GREEN: 3>
Using :class:`object`
@ -1194,10 +1185,24 @@ Using :class:`object` would look like::
... GREEN = object()
... BLUE = object()
...
>>> Color.GREEN # doctest: +SKIP
<Color.GREEN: <object object at 0x...>>
This is also a good example of why you might want to write your own
:meth:`__repr__`::
>>> class Color(Enum):
... RED = object()
... GREEN = object()
... BLUE = object()
... def __repr__(self):
... return "<%s.%s>" % (self.__class__.__name__, self._name_)
...
>>> Color.GREEN
<Color.GREEN>
Using a descriptive string
""""""""""""""""""""""""""
@ -1209,9 +1214,7 @@ Using a string as the value would look like::
... BLUE = 'too fast!'
...
>>> Color.GREEN
<Color.GREEN>
>>> Color.GREEN.value
'go'
<Color.GREEN: 'go'>
Using a custom :meth:`__new__`
@ -1232,9 +1235,7 @@ Using an auto-numbering :meth:`__new__` would look like::
... BLUE = ()
...
>>> Color.GREEN
<Color.GREEN>
>>> Color.GREEN.value
2
<Color.GREEN: 2>
To make a more general purpose ``AutoNumber``, add ``*args`` to the signature::
@ -1257,7 +1258,7 @@ to handle any extra arguments::
... BLEACHED_CORAL = () # New color, no Pantone code yet!
...
>>> Swatch.SEA_GREEN
<Swatch.SEA_GREEN>
<Swatch.SEA_GREEN: 2>
>>> Swatch.SEA_GREEN.pantone
'1246'
>>> Swatch.BLEACHED_CORAL.pantone
@ -1384,30 +1385,9 @@ An example to show the :attr:`_ignore_` attribute in use::
... Period['day_%d' % i] = i
...
>>> list(Period)[:2]
[Period.day_0, Period.day_1]
[<Period.day_0: datetime.timedelta(0)>, <Period.day_1: datetime.timedelta(days=1)>]
>>> list(Period)[-2:]
[Period.day_365, Period.day_366]
Conforming input to Flag
^^^^^^^^^^^^^^^^^^^^^^^^
To create a :class:`Flag` enum that is more resilient to out-of-bounds results
from mathematical operations, you can use the :attr:`FlagBoundary.CONFORM`
setting::
>>> from enum import Flag, CONFORM, auto
>>> class Weekday(Flag, boundary=CONFORM):
... MONDAY = auto()
... TUESDAY = auto()
... WEDNESDAY = auto()
... THURSDAY = auto()
... FRIDAY = auto()
... SATURDAY = auto()
... SUNDAY = auto()
>>> today = Weekday.TUESDAY
>>> Weekday(today + 22) # what day is three weeks from tomorrow?
>>> Weekday.WEDNESDAY
[<Period.day_365: datetime.timedelta(days=365)>, <Period.day_366: datetime.timedelta(days=366)>]
.. _enumtype-examples: