Using Queue in python

Question

I'm trying to run the following in Eclipse (using PyDev) and I keep getting error :

q = queue.Queue(maxsize=0) NameError: global name 'queue' is not defined

I've checked the documentations and appears that is how its supposed to be placed. Am I missing something here? Is it how PyDev works? or missing something in the code? Thanks for all help.

from queue import *

def worker():
    while True:
        item = q.get()
        do_work(item)
        q.task_done()

def main():

    q = queue.Queue(maxsize=0)
    for i in range(num_worker_threads):
         t = Thread(target=worker)
         t.daemon = True
         t.start()

    for item in source():
        q.put(item)

    q.join()       # block until all tasks are done

main()

Using: Eclipse SDK

Version: 3.8.1 Build id: M20120914-1540

and Python 3.3

Renato Byrro · Accepted Answer · 2020-12-10 09:39:51Z

27

You do

from queue import *

This imports all the classes from the queue module already. Change that line to

q = Queue(maxsize=0)

CAREFUL: "Wildcard imports (from import *) should be avoided, as they make it unclear which names are present in the namespace, confusing both readers and many automated tools". (Python PEP-8)

As an alternative, one could use:

from queue import Queue

q = Queue(maxsize=0)

edited Dec 10, 2020 at 9:39

Renato Byrro

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answered Jan 29, 2013 at 14:16

David Robinson

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3 Comments

Bain Over a year ago

Thank you! Now why does it do that? I thought importing them all via the * works better or something.

David Robinson Over a year ago

It's not about working better or worse- it's that when you use the from queue at the top you no longer need to specify queue. when you call it. In some ways that is "better" (it's a shorter line of code) in some ways it is "worse" (someone reading the code doesn't know where that class came from)

NoBugs Over a year ago

It should probably be noted that this is considered bad practice for big projects - "PEP-8 recommends avoiding wildcard imports ( from some_module import * ), and it’s absolutely right. One of the most exciting reasons is that it opens your code up to some interesting ways to break in a multideveloper environment." How to Make Mistakes in Python

Ashwini Chaudhary · Accepted Answer · 2013-01-29 14:16:13Z

7

That's because you're using : from queue import *

and then you're trying to use :

queue.Queue(maxsize=0)

remove the queue part, because from queue import * imports all the attributes to the current namespace. :

Queue(maxsize=0)

or use import queue instead of from queue import *.

answered Jan 29, 2013 at 14:16

Ashwini Chaudhary

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Comments

Mahadev Vyavahare · Accepted Answer · 2020-07-24 09:55:58Z

2

make sure your code is not under queue.py rename it to something else. if your file name is queue.py it will try to search in the same file.

answered Jul 24, 2020 at 9:55

Mahadev Vyavahare

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1 Comment

Badhan Sen Over a year ago

Thanks @Mahadev. I named my file queue.py and it was not working. After renaming the file, the issue was resolved.

Vladyslav · Accepted Answer · 2017-07-13 19:21:17Z

1

If you import from queue import * this is mean that all classes and functions importing in you code fully. So you must not write name of the module, just q = Queue(maxsize=100). But if you want use classes with name of module: q = queue.Queue(maxsize=100) you mast write another import string: import queue, this is mean that you import all module with all functions not only all functions that in first case.

answered Jul 13, 2017 at 19:21

Vladyslav

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Comments

Mark Francis · Accepted Answer · 2016-07-24 00:15:57Z

-5

You Can install kombu with pip install kombu

and then Import queue Just like this

from kombu import Queue

answered Jul 24, 2016 at 0:15

Mark Francis

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1 Comment

Jan Černý Over a year ago

Why would anyone do this if Queue is implemented to python by default ?

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