Returns a hexdigest of all the python files in the module.

def dev_version():
  """
  Returns a hexdigest of all the python files in the module.
  """

  md5_hash = hashlib.md5()
  py_files = sorted(list_files(suffix=".py"))
  if not py_files:
    return ''
  for filename in py_files:
    with open(filename, 'rb') as fobj:
      content = fobj.read()
    md5_hash.update(content)
  return md5_hash.hexdigest()