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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 realpath(self, spec, key):
 """ Resolve and update the path key in the spec with its realpath, based on the working directory. """


        if key not in spec:
            # do nothing for now
            return

        if not spec[key]:
            logger.warning(
                "cannot resolve realpath of '%s' as it is not defined", key)
            return

        check = realpath(join(spec.get(WORKING_DIR, ''), spec[key]))
        if check != spec[key]:
            spec[key] = check
            logger.warning(
                "realpath of '%s' resolved to '%s', spec is updated",
                key, check
            )
        return check