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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 _validate_dict_data(self, expected, actual):
 """Validate dictionary data. Compare expected dictionary data vs actual dictionary data. The values in the 'expected' dictionary can be strings, bools, ints, longs, or can be a function that evaluates a variable and returns a bool. """

        self.log.debug('actual: {}'.format(repr(actual)))
        self.log.debug('expected: {}'.format(repr(expected)))

        for k, v in six.iteritems(expected):
            if k in actual:
                if (isinstance(v, six.string_types) or
                        isinstance(v, bool) or
                        isinstance(v, six.integer_types)):
                    # handle explicit values
                    if v != actual[k]:
                        return "{}:{}".format(k, actual[k])
                # handle function pointers, such as not_null or valid_ip
                elif not v(actual[k]):
                    return "{}:{}".format(k, actual[k])
            else:
                return "key '{}' does not exist".format(k)
        return None