Swap keys for unique values in a dictionary in Python

Question

a = {0: \'PtpMotion\', 1: \'PtpMotion\', 2: \'LinMotion\', 3: \'LinMotion\', 4: \'LinMotion\', 5: \'LinMotion\', 6: \'LinMotion\', 7: \'LinMotion\', 8: \'LinMotion\', 9:         


        

Answer 1

When you say

b[val] = key

and val already exists,it overrides the setting, getting what you see. To get all values, you must map the original values to lists of keys, such as

from collections import defaultdict

b = defaultdict(list)
for key, val in a.items():
    b[val].append(key)
print b

When I do it (python 2.5.1), I get

defaultdict(, {'LinMotion': [2, 3, 4, 5, 6, 7, 8, 10], 
                            'PtpMotion': [0, 1, 9], 
                            'Wait': [11]})