trying to import RPi.GPIO in module

[ridgerunnersjw]

Can someone tell me how to successfully import RPi.GPIO and use it within methods within a class.....

I have s.py :

import RPi.GPIO as GPIO
class xxx:
GPIO.setmode(GPIO.BOARD)

def func(self):
GPIO.setup.......etc...

CLI Error NameError: name 'GPIO' is not defined

thank you
Steve

[hippy]

This works for me, Pi 3B, Buster, Python 2.7 and Python 3 ...

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import RPi.GPIO as GPIO

class xxx:
  GPIO.setmode(GPIO.BOARD)
  print("[1]")

  def configure(self):
    GPIO.setmode(GPIO.BOARD)
    GPIO.setwarnings(False)
    print("[2]")

x = xxx()
x.configure()

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pi@Pi3B:~/tmp $ python s.py
[1]
[2]
pi@Pi3B:~/tmp $ python3 s.py
[1]
[2]

Perhaps post your full code as that may reveal where the issue lies.

[ridgerunnersjw]

Here's code...I'm new to Python / Pi, so I'm sure I'm doing something semantically wrong:

import RPi.GPIO as gpio

class servoSL500:
"""....mxxDC (Duty Cycle) values are % of Period which is in ms"""
def __init__(self, minDC = 2, maxDC = 11, pwmPeriod = 20, boardPin = 12):
"""constructor for servoSL500"""
self.minDC = minDC
self.maxDC = maxDC
self.pwmPeriod = pwmPeriod
self.boardPin = boardPin
self.currentValue = 2
gpio.cleanup()
gpio.setmode(gpio.BOARD)

def setPwm(self, gpio):
"""move servo to a position bounded by 0 - 180 degrees"""
while(1):
newValue = input ("Enter the pulse width between " + str(self.minDC) + " and " + str(self.maxDC) + " ")
if ((self.minDC > float(newValue)) or (self.maxDC < float(newValue))):
print ("try again, value out of bound")
continue
else:
break
self.currentValue = float(newValue)
gpio.setup(self.boardPin, gpio.OUT)
t = self.gpio.PWM(self.boardPin, float(1000/self.pwmPeriod))
t.start(self.currentValue)
return 0


The error I keep getting is
AttributeError: 'servoSL500' object has no attribute 'gpio' on line gpio.setup(self.boardPin, gpio.OUT)

thanks

[Paul Hutch]

It's hard to tell without the essential Python formatting, please use the code tags to preserve formatting of code.

However I think the problem is that:

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def setPwm(self, gpio):

Should be:

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def setPwm(self):

Also remove any parameter in the code that calls your setPwm().

With a global import you can reference it anywhere in the module so don't pass it as parameter inside the module.

[ridgerunnersjw]

ok....dumb question....How do I set up code tags ? I am using Geany....is it a flag somewhere or do I have to download/link a file?

[B.Goode]

ok....dumb question....How do I set up code tags ? I am using Geany....is it a flag somewhere or do I have to download/link a file?

Nothing to do with the editor on your workstation, and nothing to download.

Just use the Code 'button' (5th from the left) at the top of the forum message submission screen.

[gordon77]

You'll find it here....

Paste your code between the code boxes

[ridgerunnersjw]

Thank you....Ok I hope this helps....Anyway I have a basic servo connected to the Pi 3 and if I run the commands from CLI all works but when I create this class in python, save and then try and run from CLI the code below does not do anything....(I have shortened the code from previous examples as I am trying to track down what is going on....My CLI entry is

from steveClass.py import servoSL500
d = servoSL500()
d.setPwm()

Code is below:

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import RPi.GPIO as gpio

class servoSL500:
    """....mxxDC (Duty Cycle) values are % of Period which is in ms"""    
    def __init__(self, minDC = 2, maxDC = 11, pwmPeriod = 20, boardPin = 12):
        """constructor for servoSL500"""
        self.minDC = minDC
        self.maxDC = maxDC
        self.pwmPeriod = pwmPeriod
        self.boardPin = boardPin
        self.currentValue = 2
        gpio.cleanup()
        gpio.setmode(gpio.BOARD)
        
    def setPwm(self):
        gpio.setup(self.boardPin, gpio.OUT)
        r = gpio.PWM(self.boardPin, 50)
        r.start(2)
        return ("good")

[B.Goode]

if I run the commands from CLI all works

What commands?

In a Linux context, 'CLI' is usually taken to mean a shell prompt. That doesn't seem to be the case here?

[ghp]

Hello, when you say "the code below does not do anything", I assume there are no error messages. Did you try to print the result of the d.setPwm()-method like

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print( dd.setPwm())

just to be sure that this method is called ?

If you use a basic servo, the valid pulse with are 1 to 2 ms in the 20 ms frame==50Hz. (Some servo have slightly different values). The "r.start(2)" sets , according to the docs,

p.start(dc) # where dc is the duty cycle (0.0 <= dc <= 100.0)

1ms is 5%, 2 ms is 10%. So start(2) is possibly too small and the servo does not react. Try values between 5.0 and 10.0.
Also if the servo is already at target position, there will be no visible action.

[ridgerunnersjw]

If I print (d.setPwm()) at terminal I get "good"....
Yes the values between 2 and 11 work for this servo....

When I run from the terminal (CLI) I can issue all the gpio.commands and the servo moves as expected...

from RPi.GPIO as gpio
gpio.cleanup()
gpio.setmode(gpio.BOARD)
gpio.setup(12, gpio.OUT)
r = gpio.PWM(12, 50)
r.start(2)

My class file compiles fine and as I said if I then issue the following at the command line:

from steveClass import servoSL500
d = servoSL500
d.setPwm()

The return is
'good'

but NO servo changes

[B.Goode]

The return is
'good'

but NO servo changes

Isn't the Servo in the target position as a result of the previous test?

[ridgerunnersjw]

Yes I do change the numbers in r.start to ensure it moves but even more than this....
fundamentally import RPi.GPIO as gpio is NOT working within the file steveClass.py
if I run at CLI

import steveClass
print (servoSL500)

I get <class 'steveClass.servoSL500'>

however if I do
print (gpio)

I get
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'gpio' is not defined

Am I missing something fundamental here??

[B.Goode]

What is the result of

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import RPi.GPIO as gpio
print (gpio)

(Still unclear what this 'CLI' is that you are using.. )

[ridgerunnersjw]

sorry....CLI : Command Line Interface.....synonymous with the terminal...I open a terminal do sudo python3 in raspbian and after python opens in the terminal I run the commands one at a time

If I run the commands you requested in the terminal the result is:

<module 'RPi.GPIO' from '/usr/lib/python3/dist-packages/RPi/GPIO/__init__.py'>

but if I

import steveClass
print (gpio)

I get the aforementioned error

Is it possible that after you import the file steveClass.py that I have to do something else to get the first line in the file (import RPi.GPIO as gpio) to be "active"

[B.Goode]

Untested, but try:

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import steveClass
print (steveClass.gpio)

For the background see something like https://docs.python.org/3/tutorial/classes.html for details of Modules, Classes and Namespaces.


And I think you are performing your tests using the Python3 interpreter interactively, not the system CLI (shell) prompt.

[ridgerunnersjw]

thank you! Yes that works....Now can I lead you back to the original problem....I'm beginning to see the error of my ways....clearly with "import RPi.GPIO....."at the top of the file and NOT within the class creates grief when I

from steveClass import servoSL500

guessing at the CLI I should be typing
import steveClass
which gives me access to the gpio

thoughts?

[ridgerunnersjw]

At the end of the day...I do not know how to correctly instantiate this. I would like to test it at the terminal level and I do not completely understand how to make this happen....If I independently issue the import and calls of gpio one at a time at the command line the servo works as expected...

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import RPi.GPIO as gpio
class servoSL500:
    """....mxxDC (Duty Cycle) values are % of Period which is in ms"""    
    def __init__(self, minDC = 2, maxDC = 11, pwmPeriod = 20, boardPin = 12):
        """constructor for servoSL500"""
        self.minDC = minDC
        self.maxDC = maxDC
        self.pwmPeriod = pwmPeriod
        self.boardPin = boardPin
        self.currentValue = 2
        gpio.cleanup()
        gpio.setmode(gpio.BOARD)
        
    def setPwm(self):
        gpio.setup(self.boardPin, gpio.OUT)
        r = gpio.PWM(self.boardPin, 50)
        r.start(2)
        return ("good")

[hippy]

guessing at the CLI I should be typing
import steveClass
which gives me access to the gpio

No, it only gives you access to "steveClass".

You can only interact with "gpio" through interacting with "steveClass".

My class file compiles fine and as I said if I then issue the following at the command line:

from steveClass import servoSL500
d = servoSL500
d.setPwm()

The return is
'good'

but NO servo changes

Not sure how you are getting that. It doesn't work for me, using Python 2 or Python 3, which is what I would have expected -

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Python 2.7.16 (default, Apr  6 2019, 01:42:57) 
[GCC 8.2.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from steveClass import servoSL500
>>> d = servoSL500
>>> d.setPwm()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unbound method setPwm() must be called with servoSL500 instance as first argument (got nothing instead)
>>>

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Python 3.7.3 (default, Apr  3 2019, 05:39:12) 
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from steveClass import servoSL500
>>> d = servoSL500
>>> d.setPwm()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: setPwm() missing 1 required positional argument: 'self'
>>>

Added: Right; you earlier had "d = servoSL500()", and yes that should work.

[mattmiller]

I'd suggest writing a simple program without classes and see if your servo moves as expected

[ghp]

think "the problem" is the pwm-variable

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    def setPwm(self):
        gpio.setup(self.boardPin, gpio.OUT)
        r = gpio.PWM(self.boardPin, 50)
        r.start(2)
        return ("good")

When the method terminates, the r-variable is destroyed and PWM terminates. To vaIidate this, I added a time.sleep(10) after the r.start() and got some pulses on my oscilloscope.

When changing this variable to a class member, then it works. It's lifetime is then as long as the class itself.

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    def setPwm(self):
        print("setPwm", self.boardPin)
        self.r = gpio.PWM(self.boardPin, 50)

        self.r.start(2)
        return ("good")

[ridgerunnersjw]

Thanks for all the help from everyone....ghp you hit it on the head....sleep(1) after r.start() solves the problem!

Thanks all!!