Method __init__

Lib/inspect.py:2979–3037

Constructs Signature from the given list of Parameter objects and 'return_annotation'. All arguments are optional.

(self, parameters=None, *, return_annotation=_empty,
                 __validate_parameters__=True)

    empty = _empty

    def __init__(self, parameters=None, *, return_annotation=_empty,
                 __validate_parameters__=True):
        """Constructs Signature from the given list of Parameter
        objects and 'return_annotation'.  All arguments are optional.
        """

        if parameters is None:
            params = OrderedDict()
        else:
            if __validate_parameters__:
                params = OrderedDict()
                top_kind = _POSITIONAL_ONLY
                seen_default = False
                seen_var_parameters = set()

                for param in parameters:
                    kind = param.kind
                    name = param.name

                    if kind in (_VAR_POSITIONAL, _VAR_KEYWORD):
                        if kind in seen_var_parameters:
                            msg = f'more than one {kind.description} parameter'
                            raise ValueError(msg)

                        seen_var_parameters.add(kind)

                    if kind < top_kind:
                        msg = (
                            'wrong parameter order: {} parameter before {} '
                            'parameter'
                        )
                        msg = msg.format(top_kind.description,
                                         kind.description)
                        raise ValueError(msg)
                    elif kind > top_kind:
                        top_kind = kind

                    if kind in (_POSITIONAL_ONLY, _POSITIONAL_OR_KEYWORD):
                        if param.default is _empty:
                            if seen_default:
                                # No default for this parameter, but the
                                # previous parameter of had a default
                                msg = 'non-default argument follows default ' \
                                      'argument'
                                raise ValueError(msg)
                        else:
                            # There is a default for this parameter.
                            seen_default = True

                    if name in params:
                        msg = 'duplicate parameter name: {!r}'.format(name)
                        raise ValueError(msg)

                    params[name] = param
            else:
                params = OrderedDict((param.name, param) for param in parameters)

        self._parameters = types.MappingProxyType(params)