summaryrefslogtreecommitdiffstats
path: root/Lib/enum.py
blob: 7d58f8d17a6ed39dc1982a2811a81d3ab843fb39 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
import sys
from collections import OrderedDict
from types import MappingProxyType, DynamicClassAttribute

__all__ = ['Enum', 'IntEnum', 'unique']


def _is_descriptor(obj):
    """Returns True if obj is a descriptor, False otherwise."""
    return (
            hasattr(obj, '__get__') or
            hasattr(obj, '__set__') or
            hasattr(obj, '__delete__'))


def _is_dunder(name):
    """Returns True if a __dunder__ name, False otherwise."""
    return (name[:2] == name[-2:] == '__' and
            name[2:3] != '_' and
            name[-3:-2] != '_' and
            len(name) > 4)


def _is_sunder(name):
    """Returns True if a _sunder_ name, False otherwise."""
    return (name[0] == name[-1] == '_' and
            name[1:2] != '_' and
            name[-2:-1] != '_' and
            len(name) > 2)


def _make_class_unpicklable(cls):
    """Make the given class un-picklable."""
    def _break_on_call_reduce(self):
        raise TypeError('%r cannot be pickled' % self)
    cls.__reduce__ = _break_on_call_reduce
    cls.__module__ = '<unknown>'


class _EnumDict(dict):
    """Track enum member order and ensure member names are not reused.

    EnumMeta will use the names found in self._member_names as the
    enumeration member names.

    """
    def __init__(self):
        super().__init__()
        self._member_names = []

    def __setitem__(self, key, value):
        """Changes anything not dundered or not a descriptor.

        If an enum member name is used twice, an error is raised; duplicate
        values are not checked for.

        Single underscore (sunder) names are reserved.

        """
        if _is_sunder(key):
            raise ValueError('_names_ are reserved for future Enum use')
        elif _is_dunder(key):
            pass
        elif key in self._member_names:
            # descriptor overwriting an enum?
            raise TypeError('Attempted to reuse key: %r' % key)
        elif not _is_descriptor(value):
            if key in self:
                # enum overwriting a descriptor?
                raise TypeError('Key already defined as: %r' % self[key])
            self._member_names.append(key)
        super().__setitem__(key, value)



# Dummy value for Enum as EnumMeta explicitly checks for it, but of course
# until EnumMeta finishes running the first time the Enum class doesn't exist.
# This is also why there are checks in EnumMeta like `if Enum is not None`
Enum = None


class EnumMeta(type):
    """Metaclass for Enum"""
    @classmethod
    def __prepare__(metacls, cls, bases):
        return _EnumDict()

    def __new__(metacls, cls, bases, classdict):
        # an Enum class is final once enumeration items have been defined; it
        # cannot be mixed with other types (int, float, etc.) if it has an
        # inherited __new__ unless a new __new__ is defined (or the resulting
        # class will fail).
        member_type, first_enum = metacls._get_mixins_(bases)
        __new__, save_new, use_args = metacls._find_new_(classdict, member_type,
                                                        first_enum)

        # save enum items into separate mapping so they don't get baked into
        # the new class
        members = {k: classdict[k] for k in classdict._member_names}
        for name in classdict._member_names:
            del classdict[name]

        # check for illegal enum names (any others?)
        invalid_names = set(members) & {'mro', }
        if invalid_names:
            raise ValueError('Invalid enum member name: {0}'.format(
                ','.join(invalid_names)))

        # create our new Enum type
        enum_class = super().__new__(metacls, cls, bases, classdict)
        enum_class._member_names_ = []               # names in definition order
        enum_class._member_map_ = OrderedDict()      # name->value map
        enum_class._member_type_ = member_type

        # Reverse value->name map for hashable values.
        enum_class._value2member_map_ = {}

        # check for a __getnewargs__, and if not present sabotage
        # pickling, since it won't work anyway
        if (member_type is not object and
            member_type.__dict__.get('__getnewargs__') is None
            ):
            _make_class_unpicklable(enum_class)

        # instantiate them, checking for duplicates as we go
        # we instantiate first instead of checking for duplicates first in case
        # a custom __new__ is doing something funky with the values -- such as
        # auto-numbering ;)
        for member_name in classdict._member_names:
            value = members[member_name]
            if not isinstance(value, tuple):
                args = (value, )
            else:
                args = value
            if member_type is tuple:   # special case for tuple enums
                args = (args, )     # wrap it one more time
            if not use_args:
                enum_member = __new__(enum_class)
                if not hasattr(enum_member, '_value_'):
                    enum_member._value_ = value
            else:
                enum_member = __new__(enum_class, *args)
                if not hasattr(enum_member, '_value_'):
                    enum_member._value_ = member_type(*args)
            value = enum_member._value_
            enum_member._name_ = member_name
            enum_member.__objclass__ = enum_class
            enum_member.__init__(*args)
            # If another member with the same value was already defined, the
            # new member becomes an alias to the existing one.
            for name, canonical_member in enum_class._member_map_.items():
                if canonical_member.value == enum_member._value_:
                    enum_member = canonical_member
                    break
            else:
                # Aliases don't appear in member names (only in __members__).
                enum_class._member_names_.append(member_name)
            enum_class._member_map_[member_name] = enum_member
            try:
                # This may fail if value is not hashable. We can't add the value
                # to the map, and by-value lookups for this value will be
                # linear.
                enum_class._value2member_map_[value] = enum_member
            except TypeError:
                pass

        # double check that repr and friends are not the mixin's or various
        # things break (such as pickle)
        for name in ('__repr__', '__str__', '__format__', '__getnewargs__'):
            class_method = getattr(enum_class, name)
            obj_method = getattr(member_type, name, None)
            enum_method = getattr(first_enum, name, None)
            if obj_method is not None and obj_method is class_method:
                setattr(enum_class, name, enum_method)

        # replace any other __new__ with our own (as long as Enum is not None,
        # anyway) -- again, this is to support pickle
        if Enum is not None:
            # if the user defined their own __new__, save it before it gets
            # clobbered in case they subclass later
            if save_new:
                enum_class.__new_member__ = __new__
            enum_class.__new__ = Enum.__new__
        return enum_class

    def __call__(cls, value, names=None, *, module=None, type=None):
        """Either returns an existing member, or creates a new enum class.

        This method is used both when an enum class is given a value to match
        to an enumeration member (i.e. Color(3)) and for the functional API
        (i.e. Color = Enum('Color', names='red green blue')).

        When used for the functional API: `module`, if set, will be stored in
        the new class' __module__ attribute; `type`, if set, will be mixed in
        as the first base class.

        Note: if `module` is not set this routine will attempt to discover the
        calling module by walking the frame stack; if this is unsuccessful
        the resulting class will not be pickleable.

        """
        if names is None:  # simple value lookup
            return cls.__new__(cls, value)
        # otherwise, functional API: we're creating a new Enum type
        return cls._create_(value, names, module=module, type=type)

    def __contains__(cls, member):
        return isinstance(member, cls) and member.name in cls._member_map_

    def __delattr__(cls, attr):
        # nicer error message when someone tries to delete an attribute
        # (see issue19025).
        if attr in cls._member_map_:
            raise AttributeError(
                    "%s: cannot delete Enum member." % cls.__name__)
        super().__delattr__(attr)

    def __dir__(self):
        return (['__class__', '__doc__', '__members__', '__module__'] +
                self._member_names_)

    def __getattr__(cls, name):
        """Return the enum member matching `name`

        We use __getattr__ instead of descriptors or inserting into the enum
        class' __dict__ in order to support `name` and `value` being both
        properties for enum members (which live in the class' __dict__) and
        enum members themselves.

        """
        if _is_dunder(name):
            raise AttributeError(name)
        try:
            return cls._member_map_[name]
        except KeyError:
            raise AttributeError(name) from None

    def __getitem__(cls, name):
        return cls._member_map_[name]

    def __iter__(cls):
        return (cls._member_map_[name] for name in cls._member_names_)

    def __len__(cls):
        return len(cls._member_names_)

    @property
    def __members__(cls):
        """Returns a mapping of member name->value.

        This mapping lists all enum members, including aliases. Note that this
        is a read-only view of the internal mapping.

        """
        return MappingProxyType(cls._member_map_)

    def __repr__(cls):
        return "<enum %r>" % cls.__name__

    def __reversed__(cls):
        return (cls._member_map_[name] for name in reversed(cls._member_names_))

    def __setattr__(cls, name, value):
        """Block attempts to reassign Enum members.

        A simple assignment to the class namespace only changes one of the
        several possible ways to get an Enum member from the Enum class,
        resulting in an inconsistent Enumeration.

        """
        member_map = cls.__dict__.get('_member_map_', {})
        if name in member_map:
            raise AttributeError('Cannot reassign members.')
        super().__setattr__(name, value)

    def _create_(cls, class_name, names=None, *, module=None, type=None):
        """Convenience method to create a new Enum class.

        `names` can be:

        * A string containing member names, separated either with spaces or
          commas.  Values are auto-numbered from 1.
        * An iterable of member names.  Values are auto-numbered from 1.
        * An iterable of (member name, value) pairs.
        * A mapping of member name -> value.

        """
        metacls = cls.__class__
        bases = (cls, ) if type is None else (type, cls)
        classdict = metacls.__prepare__(class_name, bases)

        # special processing needed for names?
        if isinstance(names, str):
            names = names.replace(',', ' ').split()
        if isinstance(names, (tuple, list)) and isinstance(names[0], str):
            names = [(e, i) for (i, e) in enumerate(names, 1)]

        # Here, names is either an iterable of (name, value) or a mapping.
        for item in names:
            if isinstance(item, str):
                member_name, member_value = item, names[item]
            else:
                member_name, member_value = item
            classdict[member_name] = member_value
        enum_class = metacls.__new__(metacls, class_name, bases, classdict)

        # TODO: replace the frame hack if a blessed way to know the calling
        # module is ever developed
        if module is None:
            try:
                module = sys._getframe(2).f_globals['__name__']
            except (AttributeError, ValueError) as exc:
                pass
        if module is None:
            _make_class_unpicklable(enum_class)
        else:
            enum_class.__module__ = module

        return enum_class

    @staticmethod
    def _get_mixins_(bases):
        """Returns the type for creating enum members, and the first inherited
        enum class.

        bases: the tuple of bases that was given to __new__

        """
        if not bases:
            return object, Enum

        # double check that we are not subclassing a class with existing
        # enumeration members; while we're at it, see if any other data
        # type has been mixed in so we can use the correct __new__
        member_type = first_enum = None
        for base in bases:
            if  (base is not Enum and
                    issubclass(base, Enum) and
                    base._member_names_):
                raise TypeError("Cannot extend enumerations")
        # base is now the last base in bases
        if not issubclass(base, Enum):
            raise TypeError("new enumerations must be created as "
                    "`ClassName([mixin_type,] enum_type)`")

        # get correct mix-in type (either mix-in type of Enum subclass, or
        # first base if last base is Enum)
        if not issubclass(bases[0], Enum):
            member_type = bases[0]     # first data type
            first_enum = bases[-1]  # enum type
        else:
            for base in bases[0].__mro__:
                # most common: (IntEnum, int, Enum, object)
                # possible:    (<Enum 'AutoIntEnum'>, <Enum 'IntEnum'>,
                #               <class 'int'>, <Enum 'Enum'>,
                #               <class 'object'>)
                if issubclass(base, Enum):
                    if first_enum is None:
                        first_enum = base
                else:
                    if member_type is None:
                        member_type = base

        return member_type, first_enum

    @staticmethod
    def _find_new_(classdict, member_type, first_enum):
        """Returns the __new__ to be used for creating the enum members.

        classdict: the class dictionary given to __new__
        member_type: the data type whose __new__ will be used by default
        first_enum: enumeration to check for an overriding __new__

        """
        # now find the correct __new__, checking to see of one was defined
        # by the user; also check earlier enum classes in case a __new__ was
        # saved as __new_member__
        __new__ = classdict.get('__new__', None)

        # should __new__ be saved as __new_member__ later?
        save_new = __new__ is not None

        if __new__ is None:
            # check all possibles for __new_member__ before falling back to
            # __new__
            for method in ('__new_member__', '__new__'):
                for possible in (member_type, first_enum):
                    target = getattr(possible, method, None)
                    if target not in {
                            None,
                            None.__new__,
                            object.__new__,
                            Enum.__new__,
                            }:
                        __new__ = target
                        break
                if __new__ is not None:
                    break
            else:
                __new__ = object.__new__

        # if a non-object.__new__ is used then whatever value/tuple was
        # assigned to the enum member name will be passed to __new__ and to the
        # new enum member's __init__
        if __new__ is object.__new__:
            use_args = False
        else:
            use_args = True

        return __new__, save_new, use_args


class Enum(metaclass=EnumMeta):
    """Generic enumeration.

    Derive from this class to define new enumerations.

    """
    def __new__(cls, value):
        # all enum instances are actually created during class construction
        # without calling this method; this method is called by the metaclass'
        # __call__ (i.e. Color(3) ), and by pickle
        if type(value) is cls:
            # For lookups like Color(Color.red)
            return value
        # by-value search for a matching enum member
        # see if it's in the reverse mapping (for hashable values)
        try:
            if value in cls._value2member_map_:
                return cls._value2member_map_[value]
        except TypeError:
            # not there, now do long search -- O(n) behavior
            for member in cls._member_map_.values():
                if member.value == value:
                    return member
        raise ValueError("%s is not a valid %s" % (value, cls.__name__))

    def __repr__(self):
        return "<%s.%s: %r>" % (
                self.__class__.__name__, self._name_, self._value_)

    def __str__(self):
        return "%s.%s" % (self.__class__.__name__, self._name_)

    def __dir__(self):
        added_behavior = [m for m in self.__class__.__dict__ if m[0] != '_']
        return (['__class__', '__doc__', '__module__', 'name', 'value'] +
                added_behavior)

    def __format__(self, format_spec):
        # mixed-in Enums should use the mixed-in type's __format__, otherwise
        # we can get strange results with the Enum name showing up instead of
        # the value

        # pure Enum branch
        if self._member_type_ is object:
            cls = str
            val = str(self)
        # mix-in branch
        else:
            cls = self._member_type_
            val = self.value
        return cls.__format__(val, format_spec)

    def __getnewargs__(self):
        return (self._value_, )

    def __hash__(self):
        return hash(self._name_)

    # DynamicClassAttribute is used to provide access to the `name` and
    # `value` properties of enum members while keeping some measure of
    # protection from modification, while still allowing for an enumeration
    # to have members named `name` and `value`.  This works because enumeration
    # members are not set directly on the enum class -- __getattr__ is
    # used to look them up.

    @DynamicClassAttribute
    def name(self):
        """The name of the Enum member."""
        return self._name_

    @DynamicClassAttribute
    def value(self):
        """The value of the Enum member."""
        return self._value_


class IntEnum(int, Enum):
    """Enum where members are also (and must be) ints"""


def unique(enumeration):
    """Class decorator for enumerations ensuring unique member values."""
    duplicates = []
    for name, member in enumeration.__members__.items():
        if name != member.name:
            duplicates.append((name, member.name))
    if duplicates:
        alias_details = ', '.join(
                ["%s -> %s" % (alias, name) for (alias, name) in duplicates])
        raise ValueError('duplicate values found in %r: %s' %
                (enumeration, alias_details))
    return enumeration