Python finding the index of a repeated element in list

Question

Consider a list as follows:

entry = [ 'document1', 'document2', 'document1', 'document2' ]

Now if I run the following piece of code:

for i in entry:
   print i + "has index" + entry.index(i)

It gives the output as

document1 has index 0
document2 has index 1
document1 has index 0
document2 has index 1

But the output should be:

document1 has index 0
document2 has index 1
document1 has index 2
document2 has index 3

Can anyone help me what should I edit in this code?

PS: I would like to use a function rather than introducing a dummy variable which is incremented along with the list.

Answer 1

You could write your own function (which uses enumerate) and use it in your code - then your code won't be cluttered with extraneous distrations:

from collections import defaultdict
def element_indices(entry):
    result = defaultdict(list)
    for ndx, element in enumerate(entry):
        result[element].append(ndx)
    return result

Usage:

entry = [ 'document1', 'document2', 'document1', 'document2' ]
for element, indices in element_indices(entry).items():
    print '{} is found at indices {}'.format(element, indices)

# >>> 
# document1 is found at indices [0, 2]
# document2 is found at indices [1, 3]
# >>> 

Answer 2

As the comments suggest, you want enumerate() :

for n, item in enumerate(entry):
    print item + " has index " + str(n)

This is the standard, idiomatic way to do what you want in Python.

Your desire to avoid using a "dummy" variable, as you call it, is perplexing; If there is some particular reason for that restriction, it would be helpful if you mentioned that in your question.