diff --git a/pepdraft-0435.txt b/pepdraft-0435.txt index 4747868ce..a61b45644 100644 --- a/pepdraft-0435.txt +++ b/pepdraft-0435.txt @@ -64,8 +64,10 @@ Module & type name ================== We propose to add a module named ``enum`` to the standard library. The main -type exposed by this module is ``Enum``. +type exposed by this module is ``Enum``. Hence, to import the ``Enum`` type +user code will run:: + >>> from enum import Enum Proposed semantics for the new enumeration type =============================================== @@ -76,8 +78,8 @@ Creating an Enum Enumerations are created using the class syntax, which makes them easy to read and write. Every enumeration value must have a unique integer value and the only restriction on their names is that they must be valid Python identifiers. -To define an enumeration, derive from the Enum class and add attributes with -assignment to their integer values. +To define an enumeration, derive from the ``Enum`` class and add attributes with +assignment to their integer values:: >>> from enum import Enum >>> class Colors(Enum): @@ -85,7 +87,7 @@ assignment to their integer values. ... green = 2 ... blue = 3 -Enumeration values are compared by identity. +Enumeration values are compared by identity:: >>> Colors.red is Colors.red True @@ -96,17 +98,17 @@ Enumeration values are compared by identity. >>> Colors.blue is Colors.red False -Enumeration values have nice, human readable string representations... +Enumeration values have nice, human readable string representations:: >>> print(Colors.red) Colors.red -...while their repr has more information. +...while their repr has more information:: >>> print(repr(Colors.red)) -The enumeration value names are available through the class members. +The enumeration value names are available through the class members:: >>> for member in Colors.__members__: ... print(member) @@ -115,13 +117,13 @@ The enumeration value names are available through the class members. blue Let's say you wanted to encode an enumeration value in a database. You might -want to get the enumeration class object from an enumeration value. +want to get the enumeration class object from an enumeration value:: >>> cls = Colors.red.enum >>> print(cls.__name__) Colors -Enums also have a property that contains just their item name. +Enums also have a property that contains just their item name:: >>> print(Colors.red.name) red @@ -130,21 +132,21 @@ Enums also have a property that contains just their item name. >>> print(Colors.blue.name) blue -The str and repr of the enumeration class also provides useful information. +The str and repr of the enumeration class also provides useful information:: >>> print(Colors) >>> print(repr(Colors)) -You can extend previously defined Enums by subclassing. +You can extend previously defined Enums by subclassing:: >>> class MoreColors(Colors): ... pink = 4 ... cyan = 5 When extended in this way, the base enumeration's values are identical to the -same named values in the derived class. +same named values in the derived class:: >>> Colors.red is MoreColors.red True @@ -153,7 +155,7 @@ same named values in the derived class. However, these are not doing comparisons against the integer equivalent values, because if you define an enumeration with similar item names and -integer values, they will not be identical. +integer values, they will not be identical:: >>> class OtherColors(Enum): ... red = 1 @@ -164,7 +166,7 @@ integer values, they will not be identical. >>> Colors.blue is not OtherColors.blue True -These enumeration values are not equal, nor do they hash equally. +These enumeration values are not equal, nor do they hash equally:: >>> Colors.red == OtherColors.red False @@ -172,7 +174,7 @@ These enumeration values are not equal, nor do they hash equally. 2 Ordered comparisons between enumeration values are *not* supported. Enums are -not integers! +not integers:: >>> Colors.red < Colors.blue Traceback (most recent call last): @@ -191,14 +193,14 @@ not integers! ... NotImplementedError -Equality comparisons are defined though. +Equality comparisons are defined though:: >>> Colors.blue == Colors.blue True >>> Colors.green != Colors.blue True -Enumeration values do not support ordered comparisons. +Enumeration values do not support ordered comparisons:: >>> Colors.red < Colors.blue Traceback (most recent call last): @@ -222,7 +224,7 @@ Enumeration values do not support ordered comparisons. NotImplementedError While equality comparisons are allowed, comparisons against non-enumeration -values will always compare not equal. +values will always compare not equal:: >>> Colors.green == 2 False @@ -235,7 +237,7 @@ values will always compare not equal. If you really want the integer equivalent values, you can convert enumeration values explicitly using the ``int()`` built-in. This is quite convenient for -storing enums in a database for example. +storing enums in a database for example:: >>> int(Colors.red) 1 @@ -244,8 +246,8 @@ storing enums in a database for example. >>> int(Colors.blue) 3 -You can also convert back to the enumeration value by calling the Enum class, -passing in the integer value for the item you want. +You can also convert back to the enumeration value by calling the Enum subclass, +passing in the integer value for the item you want:: >>> Colors(1) @@ -256,14 +258,14 @@ passing in the integer value for the item you want. >>> Colors(1) is Colors.red True -The Enum class also accepts the string name of the enumeration value. +The Enum subclass also accepts the string name of the enumeration value:: >>> Colors('red') >>> Colors('blue') is Colors.blue True -You get exceptions though, if you try to use invalid arguments. +You get exceptions though, if you try to use invalid arguments:: >>> Colors('magenta') Traceback (most recent call last): @@ -275,7 +277,7 @@ You get exceptions though, if you try to use invalid arguments. ValueError: 99 The Enum base class also supports getitem syntax, exactly equivalent to the -class's call semantics. +class's call semantics:: >>> Colors[1] @@ -299,7 +301,7 @@ class's call semantics. ValueError: 99 The integer equivalent values serve another purpose. You may not define two -enumeration values with the same integer value. +enumeration values with the same integer value:: >>> class Bad(Enum): ... cartman = 1 @@ -311,7 +313,7 @@ enumeration values with the same integer value. ... TypeError: Multiple enum values: 3 -You also may not duplicate values in derived enumerations. +You also may not duplicate values in derived enumerations:: >>> class BadColors(Colors): ... yellow = 4 @@ -321,14 +323,14 @@ You also may not duplicate values in derived enumerations. TypeError: Multiple enum values: 2 The Enum class support iteration. Enumeration values are returned in the -sorted order of their integer equivalent values. +sorted order of their integer equivalent values:: >>> [v.name for v in MoreColors] ['red', 'green', 'blue', 'pink', 'cyan'] >>> [int(v) for v in MoreColors] [1, 2, 3, 4, 5] -Enumeration values are hashable, so they can be used in dictionaries and sets. +Enumeration values are hashable, so they can be used in dictionaries and sets:: >>> apples = {} >>> apples[Colors.red] = 'red delicious' @@ -342,7 +344,7 @@ Enumeration values are hashable, so they can be used in dictionaries and sets. Pickling -------- -Enumerations created with the class syntax can also be pickled and unpickled: +Enumerations created with the class syntax can also be pickled and unpickled:: >>> from enum.tests.fruit import Fruit >>> from pickle import dumps, loads @@ -358,25 +360,25 @@ which takes an iterable object or dictionary to provide the item names and values. ``make()`` is a static method. The first argument to ``make()`` is the name of the enumeration, and it returns -the so-named `Enum` subclass. The second argument is a `source` which can be -either an iterable or a dictionary. In the most basic usage, `source` returns +the so-named `Enum` subclass. The second argument is a *source* which can be +either an iterable or a dictionary. In the most basic usage, *source* returns a sequence of strings which name the enumeration items. In this case, the values are automatically assigned starting from 1:: - >>> from enum import make - >>> make('Animals', ('ant', 'bee', 'cat', 'dog')) + >>> import enum + >>> enum.make('Animals', ('ant', 'bee', 'cat', 'dog')) The items in source can also be 2-tuples, where the first item is the enumeration value name and the second is the integer value to assign to the -value. If 2-tuples are used, all items must be 2-tuples. +value. If 2-tuples are used, all items must be 2-tuples:: >>> def enumiter(): ... start = 1 ... while True: ... yield start ... start <<= 1 - >>> make('Flags', zip(list('abcdefg'), enumiter())) + >>> enum.make('Flags', zip(list('abcdefg'), enumiter())) @@ -402,24 +404,24 @@ common values in derived classes are identical (a singleton model). While PEP complexity, though minimal, is hidden from users of the enumeration. Unlike PEP 354, enumeration values can only be tested by identity comparison. -This is to emphasis the fact that enumeration values are singletons, much like +This is to emphasise the fact that enumeration values are singletons, much like ``None``. Acknowledgments =============== -The ``flufl.enum`` implementation is based on an example by Jeremy Hylton. It -has been modified and extended by Barry Warsaw for use in the `GNU Mailman`_ -project. Ben Finney is the author of the earlier enumeration PEP 354. - -.. _`GNU Mailman`: http://www.list.org +This PEP describes the ``flufl.enum`` package by Barry Warsaw. ``flufl.enum`` +is based on an example by Jeremy Hylton. It has been modified and extended +by Barry Warsaw for use in the GNU Mailman [#]_ project. Ben Finney is the +author of the earlier enumeration PEP 354. References ========== .. [#] http://mail.python.org/pipermail/python-ideas/2013-January/019003.html .. [#] http://mail.python.org/pipermail/python-ideas/2013-February/019373.html +.. [#] http://www.list.org Copyright ========= @@ -429,10 +431,15 @@ This document has been placed in the public domain. Todo ==== - * Mark PEP 354 "superseded by" this one - * New package name within stdlib - * ``from enum import make`` creates a not-very-descriptive "make" name. Maybe - ``make_enum`` or ``enum`` is better? + * Mark PEP 354 "superseded by" this one, if accepted + * New package name within stdlib - enum? (top-level) + * "Convenience API" says "make() is a static method" - what does this mean? + make seems to be a simple module-level function in the implementation. + * For make, can we add an API like namedtuple's? + make('Animals, 'ant bee cat dog') + I.e. when make sees a string argument it splits it, making it similar to a + tuple but with far less manual quote typing. OTOH, it just saves a ".split" + so may not be worth the effort ? .. Local Variables: