Thursday, May 26, 2022

[SOLVED] Trying to create import module for Python (for RPi GPIO)

Issue

I am new to Python. I am trying to create a fake GPIO module for my Raspberry Pi that uses PWM motors so that my interpreter (using Visual Studio Code) can understand it and pass it without error.

This is what I wanted to achieve:

#Motor.py

import RPi.GPIO as GPIO

GPIO.PWM(16,100).start(0)

This is the fake module I have attempted to create after attempting to learn the basic way how python handles modules

#RPi/GPIO.py
#(RPi folder has an empty __init__.py file along with the GPIO.py file)

BOARD = 1
IN = 1
OUT = 1

def setmode(a):
   print(a)
def setup(a):
   print(a)
def output(a):
   print(a)

def PWM(a, b):
   print(a)
   def start(c):
      print(c)

The error I have gotten shows like this: AttributeError: 'NoneType' object has no attribute 'start'

I do not know how to properly create modules where it could work with multiple periods. How should I fix it so that it would achieve what I want?


Solution

GPIO.PWM is a class - and start is a member function of that class.

So you'll need to look at how classes are constructed using the __init__() method, and how member functions work.

Here is an example of the PWM class you'll need to create:

class PWM:

    def __init__(self, channel, frequency):

        print(f"PWM({channel},{frequency})");

    def start(self, duty_cycle):

        print(f"PWM.start({duty_cycle})")

So looking at GPIO.PWM(16,100).start(0) - this would first construct a PWM object by calling the PWM __init__() method - and then call the start() method on that object.

You can also split this into two calls if you need the PWM object. i.e.

motor_pwm = GPIO.PWM(16.100)
motor_pwm.start(0)

If that makes more sense?



Answered By - cguk70
Answer Checked By - Cary Denson (WPSolving Admin)
at