python - How to read first N lines of a file?

Question

We have a large raw data file that we would like to trim to a specified size.

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 1

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)