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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 _intf_ctrl(self):
 """ Retrieve variable indices of controlled models. Control interfaces are specified in ``self._ctrl``. Each ``key:value`` pair has ``key`` being the variable names for the reference idx and ``value`` being a tuple of ``(model name, field to read, destination field, return type)``. :Example: ``self._ctrl = {'syn', ('Synchronous', 'omega', 'w', list)}`` - indices: self.syn - self.w = list(system.Synchronous.omega) :return: None """


        for key, val in self._ctrl.items():
            model, field, dest, astype = val
            self.copy_data_ext(
                model, field, dest=dest, idx=self.__dict__[key], astype=astype)