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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 update_bank(self, bank_form):
 """Updates an existing bank. arg: bank_form (osid.assessment.BankForm):
 the form containing the elements to be updated raise: IllegalState - ``bank_form`` already used in an update transaction raise: InvalidArgument - the form contains an invalid value raise: NullArgument - ``bank_form`` is ``null`` raise: OperationFailed - unable to complete request raise: PermissionDenied - authorization failure occurred raise: Unsupported - ``bank_form`` did not originate from ``get_bank_form_for_update()`` *compliance: mandatory -- This method must be implemented.* """

        # Implemented from template for
        # osid.resource.BinAdminSession.update_bin_template
        if self._catalog_session is not None:
            return self._catalog_session.update_catalog(catalog_form=bank_form)
        collection = JSONClientValidated('assessment',
                                         collection='Bank',
                                         runtime=self._runtime)
        if not isinstance(bank_form, ABCBankForm):
            raise errors.InvalidArgument('argument type is not an BankForm')
        if not bank_form.is_for_update():
            raise errors.InvalidArgument('the BankForm is for update only, not create')
        try:
            if self._forms[bank_form.get_id().get_identifier()] == UPDATED:
                raise errors.IllegalState('bank_form already used in an update transaction')
        except KeyError:
            raise errors.Unsupported('bank_form did not originate from this session')
        if not bank_form.is_valid():
            raise errors.InvalidArgument('one or more of the form elements is invalid')
        collection.save(bank_form._my_map)  # save is deprecated - change to replace_one

        self._forms[bank_form.get_id().get_identifier()] = UPDATED

        # Note: this is out of spec. The OSIDs don't require an object to be returned
        return objects.Bank(osid_object_map=bank_form._my_map, runtime=self._runtime, proxy=self._proxy)