code: def classify_coupling(coupling):
      
      lower, upper = coupling
  
      if lower is None and upper is None:
          return CouplingClass.Uncoupled
      elif lower is None or upper is None:
          return CouplingClass.DirectionalReverse
      elif lower == 0.0 and upper == 0.0:
          return CouplingClass.Inconsistent
      elif lower <= 0.0 and upper >= 0.0:
          return CouplingClass.DirectionalForward
      elif abs(lower - upper) < 1e-6:
          return CouplingClass.Full
      else:
          return CouplingClass.Partial
docs: Return a constant indicating the type of coupling.
  
      Depending on the type of coupling, one of the constants from
      :class:`.CouplingClass` is returned.
  
      Args:
          coupling: Tuple of minimum and maximum flux ratio