def _format_value(value):
literal = repr(value)<EOL>try:<EOL><INDENT>if parse_value(literal) == value:<EOL><INDENT>return literal<EOL><DEDENT><DEDENT>except SyntaxError:<EOL><INDENT>pass<EOL><DEDENT>return None<EOL>
Returns `value` in a format parseable by `parse_value`, or `None`.

    Simply put, This function ensures that when it returns a string value, the
    following will hold:

        parse_value(_format_value(value)) == value

    Args:
      value: The value to format.

    Returns:
      A string representation of `value` when `value` is literally representable,
      or `None`.