code: def define_as_input(self, pin, pullup=False):
          
          self._validate_channel(pin)
          # Set bit to 1 for input or 0 for output.
          self.iodir[int(pin/8)] |= 1 << (int(pin%8))
          self._write_iodir()
          self.pullup(pin, pullup)
docs: Set the input or output mode for a specified pin.  Mode should be
          either GPIO.OUT or GPIO.IN.