Updating variables in Multi-processing

[DeaD_EyE]

Your code is ok.
Just replaced one line for testing:

import multiprocessing
from multiprocessing import Value
 
error_value = Value('i',0)  #assign as integer type
 
def get_data(url):
    try:
        raise ValueError
 
    except ValueError as e:
       #if error thrown up simply count it
        error_value.acquire()
        error_value.value += 1
        error_value.release()
        pass # <- not required, does nothing
 
 
if __name__ == '__main__':
 
# ---- Perform multi-processing 
    p = multiprocessing.Pool(6)
    results = p.map(get_data,'argslist')
    p.close()
    p.join()
 
    print(str(error_value.value))

Output:
8

This is right, because the str "argslist" consist of 8 elements.


With a context manager it's easier to handle the locking:

import multiprocessing
from multiprocessing import Value
 
error_value = Value('i',0)  #assign as integer type

def get_data(url):
    try:
        # all even numbers -> ZeroDivisionError
        if url % 2 == 0:
            1 / 0
    except ZeroDivisionError as e:
       with error_value.get_lock():
           # read/write is not an atomic operatoion
           # lock is required to do it right
           # the context manager makes the use of it easier
           error_value.value += 1
           print("ZeroDivisionError -->", url, "/ 0")
 
 
if __name__ == '__main__':
    with multiprocessing.Pool(6) as p:
        results = p.map(get_data, [0,1,2,3,4])
        # usually you should consume the results
        # actually get_data does not return explicit something
        # so it returns implicit for each call None
        for result in results:
            ...
        # pro tip: 3 dots is Ellipsis, a placeholder used for numpy
        #          I use it often to have a placeholder for missing code
        print("Total errors:", error_value.value)

multiprocessing.Pool can also used with a context manager.
Then the Pool is automatically closed, if leaving the block.

Output:
ZeroDivisionError --> 0 / 0
ZeroDivisionError --> 2 / 0
ZeroDivisionError --> 4 / 0
Total errors: 3