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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 push_func(self, cuin, callback):
 """Push a function for dfp. :param cuin: str,unicode: Callback Unique Identifier Name. :param callback: callable: Corresponding to the cuin to perform a function. :raises: DFPError,NotCallableError: raises an exception .. versionadded:: 2.3.0 """

        if cuin and isinstance(cuin, string_types) and callable(callback):
            if cuin in self._dfp_funcs:
                raise DFPError("The cuin already exists")
            else:
                self._dfp_funcs[cuin] = callback
        else:
            if not callable(callback):
                raise NotCallableError("The cuin %s cannot be called back" % cuin)
            raise DFPError("Invalid parameter")