Combining for and if loops

Question

I have the code:

num_for_loops = 0
for line in lines:
    if line.strip().startswith('for '):
        num_for_loops += 1
return num_for_loops

I need to condense it down to as little lines as possible. Is there a way to do this by combining the for and if statements? The context is irrelevant.

"I need to condense it down to as little lines as possible"? ***Why***? The context *is* relevant. — johnsyweb, May 03 '13 at 03:32
Micro-optimization: you are checking just the beginning of each line (`.startswith('for ')`), so you could replace `strip()` with `lstrip()`. — Warren Weckesser, May 03 '13 at 03:47

score 9 · Accepted Answer · answered May 03 '13 at 03:31

9

num_for_loops = sum(line.strip().startswith("for ") for line in lines)

since you're immediately returning num_for_loops I suppose you really just want

return sum(line.strip().startswith("for ") for line in lines)

answered May 03 '13 at 03:31

Nolen Royalty

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Interesting cast of `True` and `False` to 1 and 0. :-) – Kirk Strauser May 03 '13 at 03:36
Thanks exactly what I wanted to know – jevans May 03 '13 at 04:38

score 3 · Answer 2 · answered May 03 '13 at 03:35

Generator expressions always win concise code contests:

return sum(1 for line in lines if line.strip().startswith('for '))

That generates a series of 1s equal in length to the number of lines starting with 'for ', summing the list as it's generated so that you could parse terabytes of data without running out of memory.

Combining for and if loops

2 Answers2