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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 split(self, pattern=None):
 r""" Break molecule up into constituent fragments. By default (i.e., if `pattern` is `None`), each disconnected fragment is returned as a separate new `Atoms` object. This uses OpenBabel (through `OBMol.Separate`) and might not preserve atom order, depending on your version of the library. Parameters pattern : iterable of iterable of `int`, optional Groupings of atoms into molecule fragments. Each element of `pattern` should be an iterable whose members are atom indices (see example below). Returns ------- fragments : iterable of `Atoms` Examples -------- "Natural fragmentation" is the default behaviour, i.e. all disconnected fragments are returned: O -1.62893 -0.04138 0.37137 H -0.69803 -0.09168 0.09337 H -2.06663 -0.73498 -0.13663 <BLANKLINE> O 1.21457 0.03172 -0.27623 H 1.72977 -0.08038 0.53387 H 1.44927 0.91672 -0.58573 <BLANKLINE> Precise fragment grouping can be achieved by explicitly indicating which atoms belong to which fragments: O -1.62893 -0.04138 0.37137 H -0.69803 -0.09168 0.09337 H -2.06663 -0.73498 -0.13663 <BLANKLINE> H 1.72977 -0.08038 0.53387 H 1.44927 0.91672 -0.58573 <BLANKLINE> O 1.21457 0.03172 -0.27623 <BLANKLINE> """

        molecule_pybel = self.to_pybel()

        if pattern is None:
            fragments = [read_pybel(frag)
                         for frag in molecule_pybel.OBMol.Separate()]
        else:
            fragments = []
            for group in pattern:
                fragment_obmol = _pb.ob.OBMol()
                for i in group:
                    obatom = molecule_pybel.OBMol.GetAtomById(i)
                    fragment_obmol.InsertAtom(obatom)

                fragments.append(fragment_obmol)

            fragments = [read_pybel(frag) for frag in fragments]

        return fragments