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"""

Semantics of ``__missing__`` across mappings.

✅ = indicates ``__missing__`` was called

Subclass of ``dict``::

>>> d = DictSub(A = 'letter A')

>>> d['a'] # ✅

'letter A'

>>> d.get('a', '')

''

>>> 'a' in d

False

Subclass of ``UserDict``::

>>> ud = UserDictSub(A = 'letter A')

>>> ud['a'] # ✅

'letter A'

>>> ud.get('a', '') # ✅

'letter A'

>>> 'a' in ud

False

Simple subclass of ``abc.Mapping``::

>>> sms = SimpleMappingSub(A = 'letter A')

>>> sms['a']

Traceback (most recent call last):

...

KeyError: 'a'

>>> sms.get('a', '')

''

>>> 'a' in sms

False

Subclass of ``abc.Mapping`` with support for ``__missing__``::

>>> mms = MappingMissingSub(A = 'letter A')

>>> mms['a'] # ✅

'letter A'

>>> mms.get('a', '') # ✅

'letter A'

>>> 'a' in mms # ✅

True

Subclass of ``abc.Mapping`` with support for ``__missing__``::

>>> dms = DictLikeMappingSub(A = 'letter A')

>>> dms['a'] # ✅

'letter A'

>>> dms.get('a', '')

''

>>> 'a' in dms

False

"""

from collections import UserDict

from collections import abc

def _upper(x):

try:

return x.upper()

except AttributeError:

return x

class DictSub(dict):

def __missing__(self, key):

return self[_upper(key)]

class UserDictSub(UserDict):

def __missing__(self, key):

return self[_upper(key)]

class SimpleMappingSub(abc.Mapping):

def __init__(self, *args, **kwargs):

self._data = dict(*args, **kwargs)

# next three methods: abstract in ABC

def __getitem__(self, key):

return self._data[key]

def __len__(self):

return len(self._data)

def __iter__(self):

return iter(self._data)

# never called by instances of this class

def __missing__(self, key):

return self[_upper(key)]

class MappingMissingSub(SimpleMappingSub):

def __getitem__(self, key):

try:

return self._data[key]

except KeyError:

return self[_upper(key)]

class DictLikeMappingSub(SimpleMappingSub):

def __getitem__(self, key):

try:

return self._data[key]

except KeyError:

return self[_upper(key)]

def get(self, key, default=None):

return self._data.get(key, default)

def __contains__(self, key):

return key in self._data