Enumerate two python lists simultaneously?

Question

How do I enumerate two lists of equal length simultaneously? I am sure there must be a more pythonic way to do the following:

for index, value1 in enumerate(data1):
    print index, value1 + data2[index]

I want to use the index and data1[index] and data2[index] inside the for loop.

Answer 1

Use zip for both Python2 and Python3:

for index, (value1, value2) in enumerate(zip(data1, data2)):
    print(index, value1 + value2)  # for Python 2 use: `print index, value1 + value2` (no braces)

Note that zip runs only up to the shorter of the two lists(not a problem for equal length lists), but, in case of unequal length lists if you want to traverse the whole list then use itertools.izip_longest.

Answer 2

for i, (x, y) in enumerate(zip(data1, data2)):

In Python 2.x, you might want to use itertools.izip instead of zip, esp. for very long lists.

Answer 3

from itertools import count

for index, value1, value2 in zip(count(), data1, data2):
    print(index, value1, value2)

Source: http://www.saltycrane.com/blog/2008/04/how-to-use-pythons-enumerate-and-zip-to/#c2603

Answer 4

Althought this is not very clear what you look for,

>>> data1 = [3,4,5,7]
>>> data2 = [4,6,8,9]
>>> for index, value in enumerate(zip(data1, data2)):
    print index, value[0]+value[1]


0 7
1 10
2 13
3 16

Answer 5

Since it has been mentioned that the length are equal,

for l in range(0, len(a)):
   print a[l], b[l]

Answer 6

Suppose you want to use zip:

   >>> for x in zip([1,2], [3,4]):
    ...     print x
    ... 
    (1, 3)
    (2, 4)