def convert(self, argument):
    """Returns the float value of argument."""
    if (_is_integer_type(argument) or isinstance(argument, float) or
        isinstance(argument, six.string_types)):
      return float(argument)
    else:
      raise TypeError(
          'Expect argument to be a string, int, or float, found {}'.format(
              type(argument)))
Returns the float value of argument.