pylint/checkers/strings.py
def _check_new_format(self, node, func):
        """ Check the new string formatting. """
        # TODO: skip (for now) format nodes which don't have
        #       an explicit string on the left side of the format operation.
        #       We do this because our inference engine can't properly handle
        #       redefinitions of the original string.
        #       For more details, see issue 287.
        #
        # Note that there may not be any left side at all, if the format method
        # has been assigned to another variable. See issue 351. For example:
        #
        #    fmt = 'some string {}'.format
        #    fmt('arg')
        if isinstance(node.func, astroid.Attribute) and not isinstance(
            node.func.expr, astroid.Const
        ):
            return
        if node.starargs or node.kwargs:
            return
        try:
            strnode = next(func.bound.infer())
        except astroid.InferenceError:
            return
        if not (isinstance(strnode, astroid.Const) and isinstance(strnode.value, str)):
            return
        try:
            call_site = CallSite.from_call(node)
        except astroid.InferenceError:
            return

        try:
            fields, num_args, manual_pos = utils.parse_format_method_string(
                strnode.value
            )
        except utils.IncompleteFormatString:
            self.add_message("bad-format-string", node=node)
            return

        positional_arguments = call_site.positional_arguments
        named_arguments = call_site.keyword_arguments
        named_fields = {field[0] for field in fields if isinstance(field[0], str)}
        if num_args and manual_pos:
            self.add_message("format-combined-specification", node=node)
            return

        check_args = False
        # Consider "{[0]} {[1]}" as num_args.
        num_args += sum(1 for field in named_fields if field == "")
        if named_fields:
            for field in named_fields:
                if field and field not in named_arguments:
                    self.add_message(
                        "missing-format-argument-key", node=node, args=(field,)
                    )
            for field in named_arguments:
                if field not in named_fields:
                    self.add_message(
                        "unused-format-string-argument", node=node, args=(field,)
                    )
            # num_args can be 0 if manual_pos is not.
            num_args = num_args or manual_pos
            if positional_arguments or num_args:
                empty = any(True for field in named_fields if field == "")
                if named_arguments or empty:
                    # Verify the required number of positional arguments
                    # only if the .format got at least one keyword argument.
                    # This means that the format strings accepts both
                    # positional and named fields and we should warn
                    # when one of the them is missing or is extra.
                    check_args = True
        else:
            check_args = True
        if check_args:
            # num_args can be 0 if manual_pos is not.
            num_args = num_args or manual_pos
            if len(positional_arguments) > num_args:
                self.add_message("too-many-format-args", node=node)
            elif len(positional_arguments) < num_args:
                self.add_message("too-few-format-args", node=node)

        self._detect_vacuous_formatting(node, positional_arguments)
        self._check_new_format_specifiers(node, fields, named_arguments)
def _check_new_format(self, node, func):
        """ Check the new string formatting. """
        # TODO: skip (for now) format nodes which don't have
        #       an explicit string on the left side of the format operation.
        #       We do this because our inference engine can't properly handle
        #       redefinitions of the original string.
        #       For more details, see issue 287.
        #
        # Note that there may not be any left side at all, if the format method
        # has been assigned to another variable. See issue 351. For example:
        #
        #    fmt = 'some string {}'.format
        #    fmt('arg')
        if isinstance(node.func, astroid.Attribute) and not isinstance(
            node.func.expr, astroid.Const
        ):
            return
        if node.starargs or node.kwargs:
            return
        try:
            strnode = next(func.bound.infer())
        except astroid.InferenceError:
            return
        if not (isinstance(strnode, astroid.Const) and isinstance(strnode.value, str)):
            return
        try:
            call_site = CallSite.from_call(node)
        except astroid.InferenceError:
            return

        try:
            fields, num_args, manual_pos = utils.parse_format_method_string(
                strnode.value
            )
        except utils.IncompleteFormatString:
            self.add_message("bad-format-string", node=node)
            return

        positional_arguments = call_site.positional_arguments
        named_arguments = call_site.keyword_arguments
        named_fields = {field[0] for field in fields if isinstance(field[0], str)}
        if num_args and manual_pos:
            self.add_message("format-combined-specification", node=node)
            return

        check_args = False
        # Consider "{[0]} {[1]}" as num_args.
        num_args += sum(1 for field in named_fields if field == "")
        if named_fields:
            for field in named_fields:
                if field and field not in named_arguments:
                    self.add_message(
                        "missing-format-argument-key", node=node, args=(field,)
                    )
            for field in named_arguments:
                if field not in named_fields:
                    self.add_message(
                        "unused-format-string-argument", node=node, args=(field,)
                    )
            # num_args can be 0 if manual_pos is not.
            num_args = num_args or manual_pos
            if positional_arguments or num_args:
                empty = any(True for field in named_fields if field == "")
                if named_arguments or empty:
                    # Verify the required number of positional arguments
                    # only if the .format got at least one keyword argument.
                    # This means that the format strings accepts both
                    # positional and named fields and we should warn
                    # when one of the them is missing or is extra.
                    check_args = True
        else:
            check_args = True
        if check_args:
            # num_args can be 0 if manual_pos is not.
            num_args = num_args or manual_pos
            if len(positional_arguments) > num_args:
                self.add_message("too-many-format-args", node=node)
            elif len(positional_arguments) < num_args:
                self.add_message("too-few-format-args", node=node)

        self._detect_vacuous_formatting(node, positional_arguments)
        self._check_new_format_specifiers(node, fields, named_arguments)
Check the new string formatting.