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

• user1781498: The file_reader variable length might 0.

Answer 1

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