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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 swap_atom_keys(self, swap_dict, dict_key='atom_ids'):
 """ Swap a force field atom id for another user-defined value. This modified all values in :attr:`MolecularSystem.system['atom_ids']` that match criteria. This function can be used to decipher a whole forcefield if an appropriate dictionary is passed to the function. Example ------- In this example all atom ids 'he' will be exchanged to 'H'. .. code-block:: python pywindow.molecular.MolecularSystem.swap_atom_keys({'he': 'H'}) Parameters swap_dict: :class:`dict` A dictionary containg force field atom ids (keys) to be swapped with corresponding values (keys' arguments). dict_key: :class:`str` A key in :attr:`MolecularSystem.system` dictionary to perform the atom keys swapping operation on. (default='atom_ids') Returns ------- None : :class:`NoneType` """

        # Similar situation to the one from decipher_atom_keys function.
        if 'atom_ids' not in self.system.keys():
            dict_key = 'elements'
        for atom_key in range(len(self.system[dict_key])):
            for key in swap_dict.keys():
                if self.system[dict_key][atom_key] == key:
                    self.system[dict_key][atom_key] = swap_dict[key]