Python Class Method Error -- unbound requires instance

Question

I'm calling

Hardware.gpio_active(True)

This is my Hardware class:

import os
import glob
import time
import RPi.GPIO as GPIO

#class to manage hardware -- sensors, pumps, etc
class Hardware(object):
    #global vars for sensor 
    base_dir = '/sys/bus/w1/devices/'
    device_folder = glob.glob(base_dir + '28*')[0]
    device_file = device_folder + '/w1_slave'

    #global var for program
    temp_unit = 'F' #temperature unit, choose C for Celcius or F for F for Farenheit
    gpio_pin = 17 

    #function to enable GPIO
    @classmethod
    def gpio_active(active):
        #system params for sensor
        if active is True:
            os.system('modprobe w1-gpio')
            os.system('modprobe w1-therm')
            GPIO.setmode(GPIO.BCM)
            GPIO.setup(Hardware.gpio_pin, GPIO.OUT)
            print 'activating GPIO'
        else:
            print 'deactivating GPIO'
            GPIO.cleanup()

I get this error:

TypeError: unbound method gpio_active() must be called with Hardware instance as first argument (got bool instance instead)

I don't want to pass an instance -- I want gpio_active() to basically act as a function but retain accessibility to static class variables. I thought this is what @classmethod was for. I get the same error with @staticmethod.

What am I misunderstanding?

No, with staticmethod you should not be getting the same error. That's the description of staticmethod it does not implicitly pass an argument to a function. — Dimitris Fasarakis Hilliard
– Dimitris Fasarakis Hilliard, Commented Jul 27, 2016 at 3:14

Kxrr · Accepted Answer · 2016-07-27 03:01:26Z

1

Just replace def gpio_active(active) to def gpio_active(cls, active).

Read more about @classmethod here: https://julien.danjou.info/blog/2013/guide-python-static-class-abstract-methods

answered Jul 27, 2016 at 3:01

Kxrr

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2 Comments

Joenarr Bronarsson Over a year ago

Tried this earlier, same issue.

Kxrr Over a year ago

If you still get TypeError ... got bool instance instead, I guess that you may forget to save your code before run it.

DaveBensonPhillips · Accepted Answer · 2016-07-27 03:19:19Z

1

You can use a staticmethod:

@staticmethod
def gpio_active(active):
    ...

But it looks like you should be using a classmethod so you have access to other static/class methods for that class, or access to the class-level variables:

@classmethod
def gpio_active(cls, active):
    ...

Then replace Hardware.gpio_pin with cls.gpio_pin

edited Jul 27, 2016 at 3:19

answered Jul 27, 2016 at 3:03

DaveBensonPhillips

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2 Comments

Joenarr Bronarsson Over a year ago

I need access to other class methods & variables. Either way I try I get the same error : - /

DaveBensonPhillips Over a year ago

You can't be getting that error if you're doing the above. Are you sure your stacktrace isn't different in each case?

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