method
        ... def construct_from_string(cls, string):
        ...     pattern = re.compile(r"^my_type\[(?P<arg_name>.+)\]$")
        ...     match = pattern.match(string)
        ...     if match:
        ...         return cls(**match.groupdict())
        ...     else:
        ...         raise TypeError(
        ...             f"Cannot construct a '{cls.__name__}' from '{string}'"
        ...         )
        z.'construct_from_string' expects a string, got z