import sys

parts = 3
filename = "file.txt"
name, ext = filename.split('.')

data = [line for line in open(filename, "rb").read().split("\n")]

for n, part in enumerate(zip(*[iter(data)] * parts)):
	f = open('%s_part_%s.%s' % (name, n, ext), 'w')
	f.write("\n".join(part));
	f.close()