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why the method get() of python Queue is hang on there?

Hi,
I am using Queue from python2.4. Here is what happen to me:

import Queue
b = Queue.Queue(0)
b.put(9999)
b.get() # this is ok, it pops out 9999
b.get() # this one does not return anything and is hang on there

Anybody knows what is going on with the second b.get()?

ouyang

Aug 14 '06 #1
6 11391
zxoimport Queue
zxob = Queue.Queue(0)
zxob.put(9999)
zxob.get() # this is ok, it pops out 9999
zxob.get() # this one does not return anything and is hang on there

zxoAnybody knows what is going on with the second b.get()?

Queue objects are meant to be used in a multithreaded application. By
default, when the Queue is empty, a consumer calling get() will block until
a producer put()s something else into it. From the documentation:

get([block[, timeout]])
Remove and return an item from the queue. If optional args block is
true and timeout is None (the default), block if necessary until an
item is available....

Skip
Aug 14 '06 #2
import Queue
b = Queue.Queue(0)
b.put(9999)
b.get() # this is ok, it pops out 9999
b.get() # this one does not return anything and is hang on
there

Anybody knows what is going on with the second b.get()?
>>help(Queue.Queue)
:
:
| get(self, block=True, timeout=None)
| Remove and return an item from the queue.
|
| If optional args 'block' is true and
| 'timeout' is None (the default), block if
| necessary until an item is available. If
| 'timeout' is a positive number, it blocks
| at most 'timeout' seconds and raises the
| Empty exception if no item was available
| within that time. Otherwise ('block' is
| false), return an item if one is
| immediately available, else raise the
| Empty exception ('timeout' is ignored in
| that case).
|
| get_nowait(self)
| Remove and return an item from the queue
| without blocking.
|
| Only get an item if one is immediately
| available. Otherwise raise the Empty
| exception.
:
:

Notice that by default, get() will block until
there's something to read. You can use either

b.get(block=False)

or

b.get_nowait()

In either case, an exception will be raised when
the Queue is empty, to let you know as much. Just
trap for the exception and do as you please.

-tkc


Aug 14 '06 #3
zxo102 wrote:
Hi,
I am using Queue from python2.4. Here is what happen to me:

import Queue
b = Queue.Queue(0)
b.put(9999)
b.get() # this is ok, it pops out 9999
b.get() # this one does not return anything and is hang on there

Anybody knows what is going on with the second b.get()?
the documentation has the answer:

get( [block[, timeout]])

Remove and return an item from the queue. If optional args block
is true and timeout is None (the default), block if necessary until
an item is available. /.../

http://docs.python.org/lib/QueueObjects.html

</F>

Aug 14 '06 #4
On Mon, 14 Aug 2006 17:10:13 +0200, zxo102 <zx****@gmail.comwrote:
Hi,
I am using Queue from python2.4. Here is what happen to me:

import Queue
b = Queue.Queue(0)
b.put(9999)
b.get() # this is ok, it pops out 9999
b.get() # this one does not return anything and is hang on there

Anybody knows what is going on with the second b.get()?
What did you expect? Since you've done only one put in the Queue, there's
nothing left in it. Since queues are meant to communicate between threads
- and also often to synchronize them -, the default behaviour for the get
when the queue is empty is to wait for something to be put in it. If you
want your second get to fail, use the get_nowait method.

HTH
--
python -c "print ''.join([chr(154 - ord(c)) for c in
'U(17zX(%,5.zmz5(17l8(%,5.Z*(93-965$l7+-'])"
Aug 14 '06 #5
Thanks for your guys. I got it. I thought Queue can be used anywhere
in the code and the second b.get() would return a "None".

Ouyang
zxo102 写道:
Hi,
I am using Queue from python2.4. Here is what happen to me:

import Queue
b = Queue.Queue(0)
b.put(9999)
b.get() # this is ok, it pops out 9999
b.get() # this one does not return anything and is hang on there

Anybody knows what is going on with the second b.get()?

ouyang
Aug 14 '06 #6
At Monday 14/8/2006 12:35, zxo102 wrote:
>Thanks for your guys. I got it. I thought Queue can be used anywhere
in the code and the second b.get() would return a "None".
You can use a list as a generic queue, with append (== push) and pop(0)

Gabriel Genellina
Softlab SRL

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Aug 14 '06 #7

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