code: def calc_tmean_v1(self):
      
      con = self.parameters.control.fastaccess
      der = self.parameters.derived.fastaccess
      flu = self.sequences.fluxes.fastaccess
      flu.tmean = 0.
      for k in range(con.nmbzones):
          flu.tmean += der.relzonearea[k]*flu.tc[k]
docs: Calculate the areal mean temperature of the subbasin.
  
      Required derived parameter:
        |RelZoneArea|
  
      Required flux sequence:
        |TC|
  
      Calculated flux sequences:
        |TMean|
  
      Examples:
  
          Prepare two zones, the first one being twice as large
          as the second one:
  
          >>> from hydpy.models.hland import *
          >>> parameterstep('1d')
          >>> nmbzones(2)
          >>> derived.relzonearea(2.0/3.0, 1.0/3.0)
  
          With temperature values of 5°C and 8°C  of the respective zones,
          the mean temperature is 6°C:
  
          >>> fluxes.tc = 5.0, 8.0
          >>> model.calc_tmean_v1()
          >>> fluxes.tmean
          tmean(6.0)