How do I sum the first value in each tuple in a list of tuples in Python?

Question

I have a list of tuples (always pairs) like this:

[(0, 1), (2, 3), (5, 7), (2, 1)]

I\'d like to find the sum of the first items in each pai

Answer 1

A version compatible with Python 2.3 is

sum([pair[0] for pair in list_of_pairs])

or in recent versions of Python, see this answer or this one.