NameError: name 'f' is not defined when using pool.map(f, range()) in class

Question

I'm new to python and I'm trying to load the CPU using pool.map(). The following code does the loading on the CPU when it is not included in a class

def f(x):
    while True:
        x*x

def load(cores):
    print('utilizing %d cores' % (cores/2))
    pool = Pool(10)
    pool.map(f, range(6))

However, when I put it in a class and try to run the code

class test_cpu:

    def f(x):
        while True:
            x*x

    def load(cores):
        print('utilizing %d cores' % (cores/2))
        pool = Pool(10)
        pool.map(f, range(6))

if __name__ == '__main__':
    print('There are %d CPUs in your PC' % multiprocessing.cpu_count())
    cores_count = multiprocessing.cpu_count()
    input_user = input('What do you want to tes? type CPU, Memory or Both: ')
    input_user.lower()
    if input_user == 'cpu':
        test_cpu.load(cores_count)

when I type CPU it prints this error, stating that the function f is not defined

utilizing 4 cores
Traceback (most recent call last):
  File "test_all.txt", line 81, in <module>
    test_cpu.load(cores_count)
  File "test_all.txt", line 45, in load
    pool.map(f, range(6))
NameError: name 'f' is not defined

what should I do to fix this?

Answer 1

You are treating the methods as static class methods. Here are two ways to fix your code:

1. using @staticmethod. Less preferred method, uses class methods (not object-oriented):

class test_cpu:
    @staticmethod  # changed
    def f(x):
        while True:
            x * x

    @staticmethod  # changed
    def load(cores):
        print("utilizing %d cores" % (cores / 2))
        pool = Pool(10)
        pool.map(test_cpu.f, range(6))  # changed

2. adding self and creating a test_cpu instance:

import multiprocessing
from multiprocessing import Pool


class test_cpu:
    def f(self, x):  # changed
        while True:
            x * x

    def load(self, cores):  # changed
        print("utilizing %d cores" % (cores / 2))
        pool = Pool(10)
        pool.map(self.f, range(6))  # changed


if __name__ == "__main__":
    print("There are %d CPUs in your PC" % multiprocessing.cpu_count())
    cores_count = multiprocessing.cpu_count()
    input_user = input("What do you want to tes? type CPU, Memory or Both: ")
    input_user.lower()
    test_cpu_instance = test_cpu()  # changed
    if input_user == "cpu":
        test_cpu_instance.load(cores_count)  # changed