code: def _copy_number_format(other):
      
      copy = NumberFormat(pattern=other.pattern,
                          format=other.format,
                          leading_digits_pattern=list(other.leading_digits_pattern),
                          national_prefix_formatting_rule=other.national_prefix_formatting_rule,
                          national_prefix_optional_when_formatting=other.national_prefix_optional_when_formatting,
                          domestic_carrier_code_formatting_rule=other.domestic_carrier_code_formatting_rule)
      copy._mutable = True
      return copy
docs: Return a mutable copy of the given NumberFormat object