Getting index of item while processing a list using map in python

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Use enumerate:

In [3]: user_details = [{'name':x, 'rank':i} for i,x in enumerate(ranked_users)] 

In [4]: user_details
Out[4]: 
[{'name': 'jon', 'rank': 0},
 {'name': 'bob', 'rank': 1},
 {'name': 'jane', 'rank': 2},
 {'name': 'alice', 'rank': 3},
 {'name': 'chris', 'rank': 4}]

PS. My first answer was

user_details = map(lambda (i,x): {'name':x, 'rank':i}, enumerate(ranked_users))

I’d strongly recommend using a list comprehension or generator expression over map and lambda whenever possible. List comprehensions are more readable, and tend to be faster to boot.

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