For 循环 n 次迭代-Python

Question

I have a simple For Loop in a python script:

for filename in filenames:
    outline= getinfo(filename)
    outfile.write(outline)

This For Loop is part of a larger script that extracts data from HTML pages. I have nearly 6GB of html pages and want to do some test runs before I try it on all of them.

I have searched but cant find a way to make my For Loop break after n iterations (lets say 100.)

Answer 1

for filename in filenames[:100]:
    outline= getinfo(filename)
    outfile.write(outline)

The list slice filenames[:100] will truncate the list of file names to just the first 100 elements.

Answer 2

Keep a counter for your for loop. When your counter reaches, 100, break

counter = 0
for filename in filenames:
    if counter == 100:
        break
    outline= getinfo(filename)
    outfile.write(outline)
    counter += 1

Answer 3

I like @kqr's answer, but just another approach to consider, instead of taking the first 100, you could take a random n many instead:

from random import sample
for filename in sample(filenames, 10):
    # pass

Answer 4

Use the built-in function enumerate() , available in both Python 2 and 3.

for idx,filename in enumerate(filenames):
    if idx == 100:
        break
    outline= getinfo(filename)
    outfile.write(outline)

Also look at this .