从多线程python中的列表中选择项目

Question

I am a beginner in python and cant figure out how to do this: I am running a python script that puts a new value every 5-10 seconds into a list. I want to choose these elements from the list in another multithreaded python script however per thread one value, so one value shouldnt be reused, if theres no next value, then wait until next value is present. I have some code where I tried to do it but with no success:

Script that creates values:

values = ['a','b','c','d','e','f']
cap = []

while True:
    cap.append(random.choice(values))
    print cap
    time.sleep(5)

Script that needs these values:

def adding(self):

p = cap.pop()
print (p)

However in a multithreaded environment, each thread gives me the same value, even thought I want value for each thread to be different (eg remove value already used by thread) What are my options here?

Answer 1

If I understood correctly, you want to use one thread (a producer) to fill a list with values, and then a few different threads (consumers) to remove from that same list. Thus resulting with a series of consumers which have mutually exclusive subsets of the values added by the producer.

A possible outcome might be:

Producer

cap.append('a')
cap.append('c')
cap.append('b')
cap.append('f')

Consumer 1

cap.pop() # a
cap.pop() # f

Consumer 2

cap.pop() # c
cap.pop() # b

If this is the behavior you want I recommend using a thread-safe object like a Queue (python 2.*) or queue (python 3.*)

Here is one possible implementation

Producer

import Queue
values = ['a','b','c','d','e','f']
q = Queue.Queue()

while True:
    q.put(random.choice(values))
    print q
    time.sleep(5)

Consumer

val = q.get() # this call will block (aka wait) for something to be available
print(val)

Its also very important that both the producer and the consumer have access to the same instance of the of q .