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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 _add_string_to_commastring(self, field, string):
 # type: (str, str) -> bool """Add a string to a comma separated list of strings Args: field (str):
 Field containing comma separated list string (str):
 String to add Returns: bool: True if string added or False if string already present """

        if string in self._get_stringlist_from_commastring(field):
            return False
        strings = '%s,%s' % (self.data.get(field, ''), string)
        if strings[0] == ',':
            strings = strings[1:]
        self.data[field] = strings
        return True