Why is this Python while loop not working?

Question

I'm trying to count the rows in a file until there's at least 5 rows, and then stop counting.

I can't figure out why this simple while loop seems to be generating an infinite loop:

    row_count = 0
    while row_count <= 5:
        for row in file_reader:
            row_count += 1

Martijn Pieters · Accepted Answer · 2013-12-07 00:21:12Z

2

The for loop will run to completion first before the while gets a chance to test row_count.

Break out of the for loop instead:

row_count = 0
for row in file_reader:
    row_count += 1
    if row_count > 5:
        break

You can use enumerate() to generate the count:

for row_count, row in enumerate(file_reader):
    if row_count > 5:
        break

Last, but not least, there is itertools.islice():

from itertools import islice

for row in islice(file_reader, 5):
    # only first five lines are iterated over

answered Dec 7, 2013 at 0:14

Martijn Pieters

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