66 lines
1.4 KiB
Python
66 lines
1.4 KiB
Python
# This is an implementation of an idea by João S. O. Bueno (@gwidion)
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# shared privately with me, with permission to use in Fluent Python 2e.
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"""
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Testing ``WilyDict``::
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>>> adict = WilyDict()
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>>> len(adict)
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0
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>>> adict['first']
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0
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>>> adict
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{'first': 0}
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>>> adict['second']
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1
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>>> adict['third']
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2
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>>> len(adict)
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3
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>>> adict
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{'first': 0, 'second': 1, 'third': 2}
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>>> adict['__magic__']
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Traceback (most recent call last):
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...
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KeyError: '__magic__'
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Testing ``MicroEnum``::
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>>> class Flavor(MicroEnum):
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... cocoa
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... coconut
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... vanilla
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>>> Flavor.cocoa, Flavor.vanilla
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(0, 2)
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>>> Flavor[1]
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'coconut'
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"""
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class WilyDict(dict):
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def __init__(self, *args, **kwargs):
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super().__init__(*args, **kwargs)
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self.__next_value = 0
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def __missing__(self, key):
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if key.startswith('__') and key.endswith('__'):
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raise KeyError(key)
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self[key] = value = self.__next_value
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self.__next_value += 1
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return value
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class MicroEnumMeta(type):
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def __prepare__(name, bases, **kwargs):
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return WilyDict()
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def __getitem__(cls, key):
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for k, v in cls.__dict__.items():
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if v == key:
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return k
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raise KeyError(key)
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class MicroEnum(metaclass=MicroEnumMeta):
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pass
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