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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 declare(self, name):
 """Declare that a key will be set in the future. This will create a future for the key that is used to hold its result and allow awaiting it. Args: name (str):
 The unique key that will be used. """


        if name in self._data:
            raise KeyError("Declared name {} that already existed".format(name))

        self._data[name] = self._loop.create_future()