How to retrieve multiple values returned of a function called through multiprocessing.Process

Question

I have a scenario like this :

for each in content :
     pdf_output,job_id=createpdf(each)
     if pdf_output : 
        pdf_output = pdf_output + pdf_output

I am trying to parallelize the whole process .Something like this

 jobs=[]
    for each in content : 
       jobs.append(multiprocessing.Process(target=self.createpdf, args=(content)))

    for each in jobs :
         jobs.start()
    for each in jobs :
         jobs.join()

How do I sensibly do the task of

if pdf_output : 
            pdf_output = pdf_output + pdf_output

For each job ? How do I retrieve the 2 retun values sent by createpdf and work on it ? I think multiprocessing.Queue is a clue , but how do I implement this ?

Answer 1

You do not need queues for such a simple task. I would recommend to use pools. The Pool.map method can apply a function to a series of values in parallel:

import multiprocessing
def createpdf(data):
    return ("This is my pdf data: %s\n" % data, 0)


data = [ "My data", "includes", "strings and", "numbers like", 42, "and", 3.14]
number_of_processes = 5
results = multiprocessing.Pool(number_of_processes).map(createpdf, data)
outputs = [result[0] for result in results]
pdfoutput = "".join(outputs)