Generates a library signature suitable for a user agent field.

  Args:
    short_name: The short, product-specific string name for the library.
  Returns:
    A library signature string to append to user-supplied user-agent value.

def GenerateLibSig(short_name):
  """Generates a library signature suitable for a user agent field.

  Args:
    short_name: The short, product-specific string name for the library.
  Returns:
    A library signature string to append to user-supplied user-agent value.
  """
  with _UTILITY_LOCK:
    utilities_used = ', '.join([utility for utility
                                in sorted(_utility_registry)])
    _utility_registry.Clear()

  if utilities_used:
    return ' (%s, %s, %s, %s)' % (short_name, _COMMON_LIB_SIG, _PYTHON_VERSION,
                                  utilities_used)
  else:
    return ' (%s, %s, %s)' % (short_name, _COMMON_LIB_SIG, _PYTHON_VERSION)