Summing the first value in each tuple in a list over a specific range in Python

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My question is based on an earlier question and I can't find to figure out (nor find) the subsequent step I need.

Say I do have the same list of tuples, namely:

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

Also I wish to find the sum of the first values in each pair, which could be done by the simple pythonic:

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

as provided by David Z. However, in my case I only wish to sum from the first first value up until a following first value, say the first value at index N = 2. Thus, only calculate the sum of:

0 + 2 + 5 

I have been trying things like:

sum([pair[0] for pair in list_of_pairs[:,N])

but without success. Can anyone provide me with an elegant solution?

asked 1 min ago

Steyn W.

8

Summing the first value in each tuple in a list over a specific range in Python