docs: def set_function(self, f):
          """Call the provided function to return the Gauge value.
  
          The function must return a float, and may be called from
          multiple threads. All other methods of the Gauge become NOOPs.
          """
  
          def samples(self):
              return (('', {}, float(f())),)
  
          self._child_samples = types.MethodType(samples, self)