How to read first N lines of a file?

python file head
Russell picture Russell · Nov 20, 2009 · Viewed 271.6k times · Source

We have a large raw data file that we would like to trim to a specified size. I am experienced in .net c#, however would like to do this in python to simplify things and out of interest.

How would I go about getting the first N lines of a text file in python? Will the OS being used have any effect on the implementation?

Answer

John La Rooy picture John La Rooy · Nov 20, 2009

Python 2

with open("datafile") as myfile:
    head = [next(myfile) for x in xrange(N)]
print head

Python 3

with open("datafile") as myfile:
    head = [next(myfile) for x in range(N)]
print(head)

Here's another way (both Python 2 & 3)

from itertools import islice
with open("datafile") as myfile:
    head = list(islice(myfile, N))
print head

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