Tags function can have an argument.

import inspect

import logging

import time

import weakref

from functools import partial

logger = logging.getLogger(__name__)

class Tag(object):

    """``class`` that abstract tags and act as a simple container."""

    def __init__(self, name, valuable, ttl=-1):

    def __init__(self, name, valuable, ttl=-1, parent=None):

        """

        :param string name: tag name

        :param valuable: something that gives tag value, string or function

        :param valuable: something that gives tag value, string or callable

        :param None,int ttl: Time to live for caching the tags, possible values

            are:

                * None (means no ttl)

                * -1 (means infinite ttl)

                * positive integer in seconds

        :param object obj: parent object the tag is attached to, it may be

            needed for the tag callable to process the tag

        """

        self.name = name

        self._value = valuable

        self.ttl = ttl

        self.parent = parent if parent is None else weakref.proxy(parent)

        if inspect.isfunction(valuable):

            args_count = len(inspect.getargspec(valuable).args)

            if args_count > 1:

                raise Exception('Invalid number of argument for tag function')

            elif args_count == 1:

                self._value = partial(valuable, self.parent)

            else:

                self._value = valuable

        else:

            self._value = lambda: valuable

    @property

    def value(self):

        call the function.

        """

        if inspect.isfunction(self._value):

        try:

            return self._value()

        except Exception:

                logger.exception(u'Calculating tag %s failed:' % self.name)

            logger.exception(u'Calculating tag %s failed:', self.name)

            return None

        return self._value

class DynamicTags(object):

    """Set tags dynamicaly.