<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def setPrivates(self, fieldDict) : """will set self._id, self._rev and self._key field."""

        
        for priv in self.privates :
            if priv in fieldDict :
                setattr(self, priv, fieldDict[priv])
            else :
                setattr(self, priv, None)
        
        if self._id is not None :
            self.URL = "%s/%s" % (self.documentsURL, self._id)