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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 append(self, item):
 """Adds a `Polymer` to the `Assembly`. Raises ------ TypeError Raised if other is any type other than `Polymer`. """

        if isinstance(item, Polymer):
            self._molecules.append(item)
        else:
            raise TypeError(
                'Only Polymer objects can be appended to an Assembly.')
        return