python - file line count

python_line_count.py

#! /usr/bin/python

"""
Usage: ./file.line.count.py <filename>

Example: ./file.line.count.py error.log
"""

import sys

if len(sys.argv) != 2:
 print (__doc__)
 sys.exit(58)

filename = sys.argv[1]

num_of_lines = sum(1 for line in open(filename))

print num_of_lines