[Tutor] A question about None

[Alan Gauld]

On 22/08/2021 08:25, Phil wrote:
> The distance sensor outputs "None" if the distance is greater than can 
> be measured and "None", of course cannot be compared. So I came up with 
> the following which is not quite correct:
> 
> while True
>      if distance_sensor.get_distance_cm() is not None:
>          if distance_sensor.get_distance_cm() > 20:
>              motor_pair.set_default_speed(20)
>              motor_pair.start()
>          else:
>              continue
> 
>      elif distance_sensor.get_distance_cm() is not None:
>          if distance_sensor.get_distance_cm() < 20:
>              motor_pair.set_default_speed(-20)
>              motor_pair.start()
>          else:
>              continue
> 
> The idea is that if "None" returned from the sensor then nothing will 
> happen and the loop will continue until "None" is not returned. Can 
> anyone see the error of my ways?


The logic semsoverly complex, why not something like:

while True:
    value = distance_sensor.get_distance_cm()
    if not value: continue   # back to the while

    if value > 20:
       ...
    elif value < 20:
       ...
    if value == 20:
       ????

That seems to express more clearly what you stated in the text.



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Alan G
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