Using globally declared tuple for Python multiprocessing

up vote
0
down vote

favorite

I am having some trouble using a tuple globally with the multiprocessing class.

I have a code as produced below:

from multiprocessing import Pool



if __name__ == '__main__':

    jj = ()

    def f(x):

        global jj

        jj += (x*x,)



    # Section A

    #for ii in range(20):

    #    f(ii)

    #print (jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f, range(20))  

    pool.join()

    print (jj)

If I run section only B, I get the tuple jj as an empty tuple. However, if I run only section A, I get a tuple of length 20.

Why is that so?

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

Please run either section A or section B at a time. Comment out the other section not in use. I use tuple because in my original code, I have to store a lot of variables and I read that the instantiation of tuples is much faster than a list. I am not calling these values anywhere in the code.
– Shihab Khan
Nov 22 at 8:59

add a comment |

up vote
0
down vote

favorite

I am having some trouble using a tuple globally with the multiprocessing class.

I have a code as produced below:

from multiprocessing import Pool



if __name__ == '__main__':

    jj = ()

    def f(x):

        global jj

        jj += (x*x,)



    # Section A

    #for ii in range(20):

    #    f(ii)

    #print (jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f, range(20))  

    pool.join()

    print (jj)

If I run section only B, I get the tuple jj as an empty tuple. However, if I run only section A, I get a tuple of length 20.

Why is that so?

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

Please run either section A or section B at a time. Comment out the other section not in use. I use tuple because in my original code, I have to store a lot of variables and I read that the instantiation of tuples is much faster than a list. I am not calling these values anywhere in the code.
– Shihab Khan
Nov 22 at 8:59

add a comment |

up vote
0
down vote

favorite

I am having some trouble using a tuple globally with the multiprocessing class.

I have a code as produced below:

from multiprocessing import Pool



if __name__ == '__main__':

    jj = ()

    def f(x):

        global jj

        jj += (x*x,)



    # Section A

    #for ii in range(20):

    #    f(ii)

    #print (jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f, range(20))  

    pool.join()

    print (jj)

If I run section only B, I get the tuple jj as an empty tuple. However, if I run only section A, I get a tuple of length 20.

Why is that so?

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

I am having some trouble using a tuple globally with the multiprocessing class.

I have a code as produced below:

from multiprocessing import Pool



if __name__ == '__main__':

    jj = ()

    def f(x):

        global jj

        jj += (x*x,)



    # Section A

    #for ii in range(20):

    #    f(ii)

    #print (jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f, range(20))  

    pool.join()

    print (jj)

If I run section only B, I get the tuple jj as an empty tuple. However, if I run only section A, I get a tuple of length 20.

Why is that so?

python python-3.x python-multiprocessing

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

edited Nov 22 at 9:00

asked Nov 22 at 8:45

Shihab Khan

227

asked Nov 22 at 8:45

Shihab Khan

227

asked Nov 22 at 8:45

Shihab Khan

227

Please run either section A or section B at a time. Comment out the other section not in use. I use tuple because in my original code, I have to store a lot of variables and I read that the instantiation of tuples is much faster than a list. I am not calling these values anywhere in the code.
– Shihab Khan
Nov 22 at 8:59

add a comment |

Please run either section A or section B at a time. Comment out the other section not in use. I use tuple because in my original code, I have to store a lot of variables and I read that the instantiation of tuples is much faster than a list. I am not calling these values anywhere in the code.
– Shihab Khan
Nov 22 at 8:59

Please run either section A or section B at a time. Comment out the other section not in use. I use tuple because in my original code, I have to store a lot of variables and I read that the instantiation of tuples is much faster than a list. I am not calling these values anywhere in the code.
– Shihab Khan
Nov 22 at 8:59

add a comment |

1 Answer
1

active

oldest

votes

up vote
1
down vote

accepted

Ok, as Python multiprocessing global variable updates not returned to parent explains, global state is not shared among processes.

You can share state using, for example, multiprocessing.Queue.

from multiprocessing import Pool, Queue



if __name__ == "__main__":

    jj = ()

    q = Queue()



    def f(x):

        global jj

        jj += (x * x,)



    def f_multi(x):

        q.put(x * x)



    # Section A

    for ii in range(20):

        f(ii)

    print(jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f_multi, range(20))

    pool.close()



    stop = "STOP"

    q.put(stop)

    items = 

    for i in iter(q.get, stop):

        items.append(i)



    print(tuple(items))

Alternatively you can use print(tuple(sorted(items))) to get the values in the same order as Section A will produce. 4 processes are working on the task in Section B and hence the "unordered" result.

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

1

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53426937%2fusing-globally-declared-tuple-for-python-multiprocessing%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
1
down vote

accepted

Ok, as Python multiprocessing global variable updates not returned to parent explains, global state is not shared among processes.

You can share state using, for example, multiprocessing.Queue.

from multiprocessing import Pool, Queue



if __name__ == "__main__":

    jj = ()

    q = Queue()



    def f(x):

        global jj

        jj += (x * x,)



    def f_multi(x):

        q.put(x * x)



    # Section A

    for ii in range(20):

        f(ii)

    print(jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f_multi, range(20))

    pool.close()



    stop = "STOP"

    q.put(stop)

    items = 

    for i in iter(q.get, stop):

        items.append(i)



    print(tuple(items))

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

1

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

add a comment |

up vote
1
down vote

accepted

Ok, as Python multiprocessing global variable updates not returned to parent explains, global state is not shared among processes.

You can share state using, for example, multiprocessing.Queue.

from multiprocessing import Pool, Queue



if __name__ == "__main__":

    jj = ()

    q = Queue()



    def f(x):

        global jj

        jj += (x * x,)



    def f_multi(x):

        q.put(x * x)



    # Section A

    for ii in range(20):

        f(ii)

    print(jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f_multi, range(20))

    pool.close()



    stop = "STOP"

    q.put(stop)

    items = 

    for i in iter(q.get, stop):

        items.append(i)



    print(tuple(items))

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

1

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

add a comment |

up vote
1
down vote

accepted

Ok, as Python multiprocessing global variable updates not returned to parent explains, global state is not shared among processes.

You can share state using, for example, multiprocessing.Queue.

from multiprocessing import Pool, Queue



if __name__ == "__main__":

    jj = ()

    q = Queue()



    def f(x):

        global jj

        jj += (x * x,)



    def f_multi(x):

        q.put(x * x)



    # Section A

    for ii in range(20):

        f(ii)

    print(jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f_multi, range(20))

    pool.close()



    stop = "STOP"

    q.put(stop)

    items = 

    for i in iter(q.get, stop):

        items.append(i)



    print(tuple(items))

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

Ok, as Python multiprocessing global variable updates not returned to parent explains, global state is not shared among processes.

You can share state using, for example, multiprocessing.Queue.

from multiprocessing import Pool, Queue



if __name__ == "__main__":

    jj = ()

    q = Queue()



    def f(x):

        global jj

        jj += (x * x,)



    def f_multi(x):

        q.put(x * x)



    # Section A

    for ii in range(20):

        f(ii)

    print(jj)



    # Section B

    pool = Pool(processes=4)

    pool.map(f_multi, range(20))

    pool.close()



    stop = "STOP"

    q.put(stop)

    items = 

    for i in iter(q.get, stop):

        items.append(i)



    print(tuple(items))

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

edited Nov 22 at 9:32

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

answered Nov 22 at 9:26

Dušan Maďar

4,30741935

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

1

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

add a comment |

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

1

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

Thanks a lot. Actually @Dušan, the problem which I am facing is that I don't have a single variable I'd have to put in a Queue. I have a function that generates a lot of data. I'm trying to store that data from each iteration so that I can use them later on for validating/checking my results. Is there any efficient way to do that? It seems to be that I'll have to do this for each of the variables.
– Shihab Khan
Nov 22 at 9:34

You can put all variables you want to return from your function to a dict and then put that dict to the Queue, e.g. q.put({'data1': [1,2,3], 'data2': (0.5, 0.6)}).
– Dušan Maďar
Nov 22 at 9:43

This sounds like a good idea. If I can make the function return this dictionary then I don't even have to use a queue.
– Shihab Khan
Nov 22 at 9:53

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

Some of your past answers have not been well-received, and you're in danger of being blocked from answering.

Please pay close attention to the following guidance:

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Htykuut