threading with multiple variables

Question

I do have a small python script that aims to run 2 to 3 function in parallel. The scripts seems to work because, I do have the answer, however, it ends with an exception:

import threading

Variable2="V2"
Variable1="V1"
Variable12="V1"
Variable22="V2"
Variable23="V3"

def func1(Variable1,Variable2):
    print ("This is my  fisrt fucntion ")
    print ("My first variable is : %s ") % (Variable1)
    print ("My second variable is : %s ") % (Variable2)

def func2(Variable12,Variable22,Variable23):
    print ("This is my  fisrt fucntion ")
    print ("My first variable is : %s ") % (Variable12)
    print ("My second variable is : %s ") % (Variable22)
    print ("My third variable is : %s ") % (Variable23)

def runInParallel(*fns):
    proc = []
    for fn, arg in fns:
        p = threading.Thread(target=fn, args=(arg,))
        p.start()
        proc.append(p)
    for p in proc:
        p.join()


runInParallel( ( func1(Variable1,Variable2,) ), (func2(Variable12,Variable22,Variable23,) ) )

It gives me the following :

This is my  fisrt fucntion
My first variable is : V1
My second variable is : V2
This is my  fisrt fucntion
My first variable is : V1
My second variable is : V2
My third variable is : V3
Traceback (most recent call last):
File "testpara.py", line 69, in <module>
    runInParallel( ( func1(Variable1,Variable2,) ) , (func2(Variable12,Variable22,Variable23,) ) )
File "testpara.py", line 61, in runInParallel
    for fn, arg in fns:
TypeError: 'NoneType' object is not iterable

I checked here And it seems one of the parameters of the threading is note passing ( group=None, target=None, name=None, args=(), kwargs={} ).

Any clue?

edit : This seems to be different from here Because variables in that answer is the same one with an updated value.

Notice that you're not passing the functions to runInParallel: you're actually evaluating those functions (both in the main thread, so there's no concurrency here) and passing the results of the two functions to runInParallel. Since both functions return None, you get the error message you're seeing. — Mark Dickinson
– Mark Dickinson, Commented Mar 25, 2017 at 14:21
Possible duplicate of Python threads not running in parallel — Mark Dickinson
– Mark Dickinson, Commented Mar 25, 2017 at 14:25
Specifically, you're missing two commas. You want: runInParallel( ( func1, (Variable1,Variable2,) ), (func2, (Variable12,Variable22,Variable23,) ) ) — Mark Dickinson
– Mark Dickinson, Commented Mar 25, 2017 at 14:26
I tried this before pasting asking my question here... Same result. Not working. — MouIdri
– MouIdri, Commented Mar 25, 2017 at 14:29

martineau · Accepted Answer · 2017-03-25 14:48:33Z

2

As pointed out by @Mark Dickinson in the comments, you're not calling runInParallel() properly, you're actually calling each function in the calling sequence (which results in the return value of each function, None, being passed as the arguments' values).

The fix is easy, just change one line in runInParallel(), and add some commas when calling it:

def runInParallel(*fns):
    proc = []
    for fn, arg in fns:
        p = threading.Thread(target=fn, args=arg)  # was args=(arg,)
        p.start()
        proc.append(p)
    for p in proc:
        p.join()

runInParallel((func1, (Variable1, Variable2,)),
              (func2, (Variable12, Variable22, Variable23,)))

Thanks to Mark Dickinson for correcting my correction. ;-)

edited Mar 25, 2017 at 14:48

answered Mar 25, 2017 at 14:31

martineau

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3 Comments

MouIdri Over a year ago

This does not pass the arguments in the runInParallel function and gives me the folowwing : "TypeError: func2() takes exactly 3 arguments (1 given)" . func1 and func2 do not have the same number of arguments..

Mark Dickinson Over a year ago

You also need to change args=(arg,) to args=arg when you create the Thread objects.

MouIdri Over a year ago

Thanks ! It was a matter of commas... I will answer my question with your corrections .

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