How to use the mypy.sametypes.is_same_type function in mypy

messages: MessageBuilder = None) -> Type:
        """Infer the correct overload item to call with given argument types.

        The return value may be CallableType or AnyType (if an unique item
        could not be determined).
        """
        messages = messages or self.msg
        # TODO: For overlapping signatures we should try to get a more precise
        #       result than 'Any'.
        match = []  # type: List[CallableType]
        best_match = 0
        for typ in overload.items():
            similarity = self.erased_signature_similarity(arg_types, arg_kinds, arg_names,
                                                          typ, context=context)
            if similarity > 0 and similarity >= best_match:
                if (match and not is_same_type(match[-1].ret_type,
                                               typ.ret_type) and
                    not mypy.checker.is_more_precise_signature(
                        match[-1], typ)):
                    # Ambiguous return type. Either the function overload is
                    # overlapping (which we don't handle very well here) or the
                    # caller has provided some Any argument types; in either
                    # case we'll fall back to Any. It's okay to use Any types
                    # in calls.
                    #
                    # Overlapping overload items are generally fine if the
                    # overlapping is only possible when there is multiple
                    # inheritance, as this is rare. See docstring of
                    # mypy.meet.is_overlapping_types for more about this.
                    #
                    # Note that there is no ambiguity if the items are
                    # covariant in both argument types and return types with

def has_no_typevars(typ: Type) -> bool:
    return is_same_type(typ, erase_typevars(typ))

min_args = max(signature.min_args, other.min_args)
            max_args = min(len(signature.arg_types), len(other.arg_types))
            if min_args > max_args:
                # Argument counts are not overlapping.
                return False
            # Signatures are overlapping iff if they are overlapping for the
            # smallest common argument count.
            for i in range(min_args):
                t1 = signature.arg_types[i]
                t2 = other.arg_types[i]
                if not is_overlapping_types(t1, t2):
                    return False
            # All arguments types for the smallest common argument count are
            # overlapping => the signature is overlapping. The overlapping is
            # safe if the return types are identical.
            if is_same_type(signature.ret_type, other.ret_type):
                return False
            # If the first signature has more general argument types, the
            # latter will never be called
            if is_more_general_arg_prefix(signature, other):
                return False
            return not is_more_precise_signature(signature, other)
    return True

def check_type_var_values(self, type: TypeInfo, actuals: List[Type], arg_name: str,
                              valids: List[Type], arg_number: int, context: Context) -> None:
        for actual in get_proper_types(actuals):
            if (not isinstance(actual, AnyType) and
                    not any(is_same_type(actual, value)
                            for value in valids)):
                if len(actuals) > 1 or not isinstance(actual, Instance):
                    self.fail('Invalid type argument value for "{}"'.format(
                        type.name), context, code=codes.TYPE_VAR)
                else:
                    class_name = '"{}"'.format(type.name)
                    actual_type_name = '"{}"'.format(actual.type.name)
                    self.fail(
                        message_registry.INCOMPATIBLE_TYPEVAR_VALUE.format(
                            arg_name, class_name, actual_type_name),
                        context,
                        code=codes.TYPE_VAR)

def is_valid_inferred_type(typ: Type) -> bool:
    """Is an inferred type valid?

    Examples of invalid types include the None type or a type with a None component.
    """
    if is_same_type(typ, NoneTyp()):
        # With strict Optional checking, we *may* eventually infer NoneTyp, but
        # we only do that if we can't infer a specific Optional type.  This
        # resolution happens in leave_partial_types when we pop a partial types
        # scope.
        return False
    if is_same_type(typ, UninhabitedType()):
        return False
    elif isinstance(typ, Instance):
        for arg in typ.args:
            if not is_valid_inferred_type(arg):
                return False
    elif isinstance(typ, TupleType):
        for item in typ.items:
            if not is_valid_inferred_type(item):
                return False
    return True

def check_argument(leftarg: Type, rightarg: Type, variance: int) -> bool:
                    if variance == COVARIANT:
                        return self._is_proper_subtype(leftarg, rightarg)
                    elif variance == CONTRAVARIANT:
                        return self._is_proper_subtype(rightarg, leftarg)
                    else:
                        return mypy.sametypes.is_same_type(leftarg, rightarg)
                # Map left type to corresponding right instances.

# Flag redefinition unless this is a reimport of a module.
                if not (node.kind == MODULE_REF and
                        self.locals[-1][name].node == node.node):
                    self.name_already_defined(name, context)
            self.locals[-1][name] = node
        elif self.type:
            self.type.names[name] = node
        else:
            existing = self.globals.get(name)
            if existing and (not isinstance(node.node, MypyFile) or
                             existing.node != node.node) and existing.kind != UNBOUND_IMPORTED:
                # Modules can be imported multiple times to support import
                # of multiple submodules of a package (e.g. a.x and a.y).
                ok = False
                # Only report an error if the symbol collision provides a different type.
                if existing.type and node.type and is_same_type(existing.type, node.type):
                    ok = True
                if not ok:
                    self.name_already_defined(name, context)
            self.globals[name] = node

def is_valid_inferred_type(typ: Type) -> bool:
    """Is an inferred type valid?

    Examples of invalid types include the None type or List[].

    When not doing strict Optional checking, all types containing None are
    invalid.  When doing strict Optional checking, only None and types that are
    incompletely defined (i.e. contain UninhabitedType) are invalid.
    """
    if is_same_type(typ, NoneTyp()):
        # With strict Optional checking, we *may* eventually infer NoneTyp, but
        # we only do that if we can't infer a specific Optional type.  This
        # resolution happens in leave_partial_types when we pop a partial types
        # scope.
        return False
    return is_valid_inferred_type_component(typ)

def visit_cast_expr(self, expr: CastExpr) -> Type:
        """Type check a cast expression."""
        source_type = self.accept(expr.expr, type_context=AnyType(), allow_none_return=True,
                                  always_allow_any=True)
        target_type = expr.type
        options = self.chk.options
        if options.warn_redundant_casts and is_same_type(source_type, target_type):
            self.msg.redundant_cast(target_type, expr)
        if 'unimported' in options.disallow_any and has_any_from_unimported_type(target_type):
            self.msg.unimported_type_becomes_any("Target type of cast", target_type, expr)
        return target_type

If a key is declared as AnyType, only update it if all the
        options are the same.
        """

        changed = False
        keys = set(key for f in frames for key in f)

        for key in keys:
            current_value = self._get(key)
            resulting_values = [f.get(key, current_value) for f in frames]
            if any(x is None for x in resulting_values):
                continue

            if isinstance(self.declarations.get(key), AnyType):
                type = resulting_values[0]
                if not all(is_same_type(type, t) for t in resulting_values[1:]):
                    type = AnyType()
            else:
                type = resulting_values[0]
                for other in resulting_values[1:]:
                    type = join_simple(self.declarations[key], type, other)
            if not is_same_type(type, current_value):
                self._push(key, type)
                changed = True

        return changed