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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 integrator(self):
 """ Get or set the intergrator module. Available integrators are: - ``'ias15'`` (default) - ``'whfast'`` - ``'sei'`` - ``'leapfrog'`` - ``'janus'`` - ``'mercurius'`` - ``'bs'`` - ``'none'`` Check the online documentation for a full description of each of the integrators. """

        i = self._integrator
        for name, _i in INTEGRATORS.items():
            if i==_i:
                return name
        return i