multiple keys in python dictionary, is possible?

问题:

I'd like to build a dictionary in python in which different keys refer to the same element. I have this dictionary:

persons = {"George":'G.MacDonald', "Luke":'G.MacDonald', "Larry":'G.MacDonald'} 

the key refer all to an identical string but the strings have different memory location inside the program, I'd like to make a dictionary in which all these keys refer to the same element, is that possible?

回答1:

You could do something like:

import itertools as it

unique_dict = {}
value_key=lambda x: x[1]
sorted_items = sorted(your_current_dict.items(), key=value_key)
for value, group in it.groupby(sorted_items, key=value_key):
    for key in group:
        unique_dict[key] = value

This transforms your dictionary into a dictionary where equal values of any kind(but comparable) are unique. If your values are not comparable(but are hashable) you could use a temporary dict:

from collections import defaultdict
unique_dict = {}
tmp_dict = defaultdict(list)

for key, value in your_current_dict.items():
    tmp_dict[value].append(key)

for value, keys in tmp_dict.items():
    unique_dict.update(zip(keys, [value] * len(keys)))

回答2:

If you happen to be using python 3, sys.intern offers a very elegant solution:

for k in persons:
    persons[k] = sys.intern(persons[k])

In Python 2.7, you can do roughly the same thing with one extra step:

interned = { v:v for v in set(persons.itervalues()) }
for k in persons:
    persons[k] = interned[persons[k]]

In 2.x (< 2.7), you can write interned = dict( (v, v) for … ) instead.