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>>> husbands2wives = bidict({'john': 'jackie'}) >>> husbands2wives['john'] # the forward mapping is just like with dict 'jackie' >>> husbands2wives[:'jackie'] # use slice for the inverse mapping 'john'
"Prefix the slice with a colon to indicate an inverse mapping. Similar to data slicing, husbands2wives["john"] has the same effect as husbands2wives["john":].
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If you don't like colons, you can use the namedbidict class to give the two-way dictionary two aliases. In this way, two sub dictionaries, forward and reverse, will be provided externally. In fact, it still exists in the form of a two-way dictionary:
>>> HTMLEntities = namedbidict('HTMLEntities', 'names', 'codepoints') >>> entities = HTMLEntities({'lt': 60, 'gt': 62, 'amp': 38}) # etc >>> entities.names['lt'] 60 >>> entities.codepoints[38] 'amp'
You can also use the unary inverse operator "~" to get the dictionary of inverse mapping of bidict.
>>> import bidict >>> from bidict import bidict >>> husbands2wives = bidict({'john': 'jackie'}) >>> ~husbands2wives bidict({'jackie': 'john'})
Pay attention to adding brackets in the following cases, because the priority of ~ is lower than that of brackets:
>>> import bidict >>> from bidict import bidict >>> husbands2wives = bidict({'john': 'jackie'}) >>> ~husbands2wives bidict({'jackie': 'john'})
Pay attention to adding brackets in the following cases, because the priority of ~ is lower than that of brackets:
>>> (~bi)['one'] 1
bidict is not a subclass of dict, but its API is a superset of dict (without the fromkeys method, the MutableMapping interface is used instead).
The iterator class inverted will flip the key and value, such as:
>>> seq = [(1, 'one'), (2, 'two'), (3, 'three')] >>> list(inverted(seq)) [('one', 1), ('two', 2), ('three', 3)]
bidict's invert() method is similar to inverted. Dependency module: MutableMapping in collections, wraps and re in functools.
bidict can be compared with dictionaries
>>> bi == bidict({1:'one'}) >>> bi == dict([(1, 'one')]) True
Other common methods of dictionaries, bidict also supports:
>>> bi.get('one') 1 >>> bi.setdefault('one', 2) 1 >>> bi.setdefault('two', 2) 2 >>> len(bi) # calls __len__ 2 >>> bi.pop('one') 1 >>> bi.popitem() ('two', 2) >>> bi.inv.setdefault(3, 'three') 'three' >>> bi bidict({'three': 3}) >>> [key for key in bi] # calls __iter__, returns keys like dict ['three'] >>> 'three' in bi # calls __contains__ True >>> list(bi.keys()) ['three'] >>> list(bi.values()) [3] >>> bi.update([('four', 4)]) >>> bi.update({'five': 5}, six=6, seven=7) >>> sorted(bi.items(), key=lambda x: x[1]) [('three', 3), ('four', 4), ('five', 5), ('six', 6), ('seven', 7)]
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