123 lines
2.4 KiB
Python
123 lines
2.4 KiB
Python
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"""
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Semantics of ``__missing__`` across mappings.
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✅ = indicates ``__missing__`` was called
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Subclass of ``dict``::
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>>> d = DictSub(A = 'letter A')
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>>> d['a'] # ✅
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'letter A'
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>>> d.get('a', '')
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''
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>>> 'a' in d
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False
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Subclass of ``UserDict``::
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>>> ud = UserDictSub(A = 'letter A')
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>>> ud['a'] # ✅
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'letter A'
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>>> ud.get('a', '') # ✅
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'letter A'
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>>> 'a' in ud
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False
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Simple subclass of ``abc.Mapping``::
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>>> sms = SimpleMappingSub(A = 'letter A')
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>>> sms['a']
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Traceback (most recent call last):
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...
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KeyError: 'a'
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>>> sms.get('a', '')
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''
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>>> 'a' in sms
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False
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Subclass of ``abc.Mapping`` with support for ``__missing__``::
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>>> mms = MappingMissingSub(A = 'letter A')
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>>> mms['a'] # ✅
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'letter A'
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>>> mms.get('a', '') # ✅
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'letter A'
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>>> 'a' in mms # ✅
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True
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Subclass of ``abc.Mapping`` with support for ``__missing__``::
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>>> dms = DictLikeMappingSub(A = 'letter A')
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>>> dms['a'] # ✅
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'letter A'
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>>> dms.get('a', '')
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''
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>>> 'a' in dms
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False
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"""
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from collections import UserDict
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from collections import abc
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def _upper(x):
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try:
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return x.upper()
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except AttributeError:
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return x
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class DictSub(dict):
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def __missing__(self, key):
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return self[_upper(key)]
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class UserDictSub(UserDict):
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def __missing__(self, key):
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return self[_upper(key)]
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class SimpleMappingSub(abc.Mapping):
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def __init__(self, *args, **kwargs):
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self._data = dict(*args, **kwargs)
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# next three methods: abstract in ABC
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def __getitem__(self, key):
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return self._data[key]
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def __len__(self):
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return len(self._data)
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def __iter__(self):
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return iter(self._data)
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# never called by instances of this class
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def __missing__(self, key):
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return self[_upper(key)]
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class MappingMissingSub(SimpleMappingSub):
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def __getitem__(self, key):
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try:
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return self._data[key]
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except KeyError:
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return self[_upper(key)]
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class DictLikeMappingSub(SimpleMappingSub):
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def __getitem__(self, key):
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try:
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return self._data[key]
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except KeyError:
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return self[_upper(key)]
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def get(self, key, default=None):
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return self._data.get(key, default)
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def __contains__(self, key):
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return key in self._data
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