Sometimes it is useful to be able to see fetch all keys in a dictionary which have a common value. The LookupDict class can do this.
Other times, when a 1 to 1 mapping of keys and values, and values to keys is needed, the ReverseDict class could be used.
Python, 37 lines
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Copy to clipboard1 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 | class ReverseDict(dict):
"""
A dictionary which can lookup values by key, and keys by value.
All values and keys must be hashable, and unique.
"""
def __init__(self, *args, **kw):
dict.__init__(self, *args, **kw)
self.reverse = dict((reversed(list(i)) for i in self.items()))
def __setitem__(self, key, value):
dict.__setitem__(self, key, value)
self.reverse[value] = key
class LookupDict(dict):
"""
A dictionary which can lookup values by key, and keys by value.
The lookup method returns a list of keys with matching values
to the value argument.
"""
def __init__(self, *args, **kw):
dict.__init__(self, *args, **kw)
def lookup(self, value):
return [item[0] for item in self.items() if item[1] == value]
if __name__ == "__main__":
a = ReverseDict(((1,2),(3,4)))
print a[1]
print a.reverse[2]
a["123"] = 67
print a["123"]
print a.reverse[67]
print "-" * 20
b = LookupDict(((1,2),(3,4),(4,2)))
print b.lookup(2)
|
The ReverseDict class must have unique values and keys, and all values and keys must be hashable.
Tags: shortcuts
