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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 activations(self):
 """Iterate over the Activations in the Agenda."""

        activation = lib.EnvGetNextActivation(self._env, ffi.NULL)

        while activation != ffi.NULL:
            yield Activation(self._env, activation)

            activation = lib.EnvGetNextActivation(self._env, activation)