code: def update_variable(self, variable, value) -> None:
          
          try:
              variable(value)
          except BaseException:
              objecttools.augment_excmessage(
                  f'When trying to update a target variable of '
                  f'{objecttools.classname(self)} `{self.name}` '
                  f'with the value(s) `{value}`')
docs: Assign the given value(s) to the given target or base variable.
  
          If the assignment fails, |ChangeItem.update_variable| raises an
          error like the following:
  
          >>> from hydpy.core.examples import prepare_full_example_2
          >>> hp, pub, TestIO = prepare_full_example_2()
          >>> item = SetItem('alpha', 'hland_v1', 'control.alpha', 0)
          >>> item.collect_variables(pub.selections)
          >>> item.update_variables()    # doctest: +ELLIPSIS
          Traceback (most recent call last):
          ...
          TypeError: When trying to update a target variable of SetItem `alpha` \
  with the value(s) `None`, the following error occurred: While trying to set \
  the value(s) of variable `alpha` of element `...`, the following error \
  occurred: The given value `None` cannot be converted to type `float`.