How to swap keys for values in a dictionary

Question

Suppose that I need to swap keys for values in dictionary.

This is what I have in mind (Assuming that the values' value is unique):

>>> my_dict = {'x':1, 'y':2, 'z':3}
>>> my_dict2 = {}
>>> for key, val in my_dict.items():
        my_dict2[val] = key

Is there any other efficient way to do it?

Answer 1

In [1]: my_dict = {'x':1, 'y':2, 'z':3}

In [2]: dict((value, key) for key, value in my_dict.iteritems())
Out[2]: {1: 'x', 2: 'y', 3: 'z'}

Answer 2

new_dict = dict( (my_dict[k], k) for k in my_dict)

or even better, but only works in Python 3:

new_dict = { my_dict[k]: k for k in my_dict}

Answer 3

Don't iterate while you modify values. Python may not even let you try.

Here's an easy way to swap:

my_dict2 = dict.fromkeys(my_dict.values(), my_dict().keys())

From http://docs.python.org/library/stdtypes.html#dict.fromkeys

Answer 4

new_dict = dict (zip(my_dict.values(),my_dict.keys()))

Answer 5

that's py3k way:

>>> my_dict = {'x':1, 'y':2, 'z':3}
>>> {v: k for k, v in my_dict.items()}
{1: 'x', 2: 'y', 3: 'z'}