Variable-variable variable in a stream
I have a basic question about multithreading in Python: I have a list and I need to change this on a thread. I understand that a list is a mutable type: How do I pass a variable by reference?
But, when I use thread, the list doesn't behave like a mutable type:
from multiprocessing import Process, Lock
def f(l, i, n):
l.acquire()
i.append(n)
l.release()
print "in:", i
if __name__ == '__main__':
lock = Lock()
i = []
for num in range(10):
p = Process(target=f, args=(lock, i, num))
p.start()
p.join()
print "out:", i
Output
in: [0]
in: [1]
in: [2]
in: [3]
in: [4]
in: [5]
in: [6]
in: [7]
in: [8]
in: [9]
out: []
Can someone please help me with this problem?
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1 answer
The code doesn't use threads, but processes that don't use memory.
Use streams:
from threading import Thread, Lock # <----
def f(l, i, n):
l.acquire()
i.append(n)
l.release()
print "in:", i
if __name__ == '__main__':
lock = Lock()
i = []
for num in range(10):
p = Thread(target=f, args=(lock, i, num)) # <----
p.start()
p.join()
print "out:", i
+4
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