How can I split a file in python?

This one splits a file up by newlines and writes it back out. You can change the delimiter easily. This can also handle uneven amounts as well, if you don’t have a multiple of splitLen lines (20 in this example) in your input file.

splitLen = 20         # 20 lines per file
outputBase="output" # output.1.txt, output.2.txt, etc.

# This is shorthand and not friendly with memory
# on very large files (Sean Cavanagh), but it works.
input = open('input.txt', 'r').read().split('\n')

at = 1
for lines in range(0, len(input), splitLen):
    # First, get the list slice
    outputData = input[lines:lines+splitLen]

    # Now open the output file, join the new slice with newlines
    # and write it out. Then close the file.
    output = open(outputBase + str(at) + '.txt', 'w')
    output.write('\n'.join(outputData))
    output.close()

    # Increment the counter
    at += 1