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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mode_key_down(self, viewer, keyname):
 """This method is called when a key is pressed and was not handled by some other handler with precedence, such as a subcanvas. """

        # Is this a mode key?
        if keyname not in self.mode_map:
            if (keyname not in self.mode_tbl) or (self._kbdmode != 'meta'):
                # No
                return False
            bnch = self.mode_tbl[keyname]
        else:
            bnch = self.mode_map[keyname]

        mode_name = bnch.name
        self.logger.debug("cur mode='%s' mode pressed='%s'" % (
            self._kbdmode, mode_name))

        if mode_name == self._kbdmode:
            # <== same key was pressed that started the mode we're in
            # standard handling is to close the mode when we press the
            # key again that started that mode
            self.reset_mode(viewer)
            return True

        if self._delayed_reset:
            # <== this shouldn't happen, but put here to reset handling
            # of delayed_reset just in case (see cursor up handling)
            self._delayed_reset = False
            return True

        if ((self._kbdmode in (None, 'meta')) or
            (self._kbdmode_type != 'locked') or (mode_name == 'meta')):
            if self._kbdmode is not None:
                self.reset_mode(viewer)

            # activate this mode
            if self._kbdmode in (None, 'meta'):
                mode_type = bnch.type
                if mode_type is None:
                    mode_type = self._kbdmode_type_default
                self.set_mode(mode_name, mode_type)
                if bnch.msg is not None:
                    viewer.onscreen_message(bnch.msg)

                return True

        return False