Why import instruction is not executed into python Process

Question

I'm looking for a solution to do multiprocessing for running script. I have a function which launches 4 process, and each process executes a script through runpy.run_path() and I get return back.

Example :

def valorise(product, dico_valo):
    res = runpy.run_path(product +"/PyScript.py", run_name="__main__")
    dico_valo[product] = res["ret"]

def f(mutex,l,dico):
    while len(l)!= 0:
        mutex.acquire()
        product = l.pop(0)
        mutex.release()
        p = Process(target=valorise, args=(product,dico))
        p.start()
        p.join()

def run_parallel_computations(valuationDate, list_scripts):
    if len(product_list)>0:
        print '\n\nPARALLEL COMPUTATIONS BEGIN..........\n\n'
        manager = Manager()
        l = manager.list(list_scripts)
        dico = manager.dict()
        mutex = Lock()
        p1 = Process(target=f, args=(mutex,l,dico), name="script1")
        p2 = Process(target=f, args=(mutex,l,dico), name="script2")
        p3 = Process(target=f, args=(mutex,l,dico), name="script3")
        p4 = Process(target=f, args=(mutex,l,dico), name="script4")
        p1.start()        
        p2.start()
        p3.start()
        p4.start()
        p1.join()
        p2.join()
        p3.join()
        p4.join()
        dico_isin = {}
        for i in iter(dico.keys()):
            dico_isin[i] = dico[i]
        return dico
        print '\n\nPARALLEL COMPUTATIONS END..........'
    else:
        print '\n\nNOTHING TO PRICE !'

In every PyScript.py, I import a library and each script has to import again it. However, in this case, it doesn't work as I want and I don't understand why. My library is imported once during the first process and the same "import" is used in the other processes. Could you help me ?

Thank you !

Answer 1

It might not be the case in multiprocessing (but looks like it is). When you will try to import something more than once (ie. import re in most of your modules), Python will not 'reimport' it. As it will see it in modules already imported and will skip it.

To force reloading you can try reload(module_name) (it can not reload import of single class/method from module, you can reload whole module or nothing)