Calculate SHA-1 of a file in Python

sha1.py

#!/usr/bin/env python
"""
usage: python -m sha1 <filename>
"""
import sys
import hashlib

# --- these fields are required for packaging
__version__ = '1.0'
__author__ = 'anatoly techtonik <techtonik@gmail.com>'
__license__ = 'Public Domain'
__url__ = 'https://gist.github.com/techtonik/df09baeacbebc52d234b'
# /-- these fields are required for packaging

if not sys.argv[1:]:
  sys.exit(__doc__.strip())

sha1sum = hashlib.sha1()
with open(sys.argv[1], 'rb') as source:
  block = source.read(2**16)
  while len(block) != 0:
    sha1sum.update(block)
    block = source.read(2**16)
print(sha1sum.hexdigest())