[Python-Dev] Making Queue.Queue easier to use
Guido van Rossum
guido at python.org
Tue Oct 11 17:12:03 CEST 2005
On 10/11/05, Nick Coghlan <ncoghlan at iinet.net.au> wrote:
> The multi-processing discussion reminded me that I have a few problems I run
> into every time I try to use Queue objects.
> My first problem is finding it:
> Py> from threading import Queue # Nope
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> ImportError: cannot import name Queue
> Py> from Queue import Queue # Ah, there it is
I don't think that's a reason to move it.
>>> from sys import Queue
ImportError: cannon import name Queue
>>> from os import Queue
ImportError: cannot import name Queue
>>> # Well where the heck is it?!
> What do people think of the idea of adding an alias to Queue into the
> threading module so that:
> a) the first line above works; and
I see no need. Code that *doesn't* need Queue but does use threading
shouldn't have to pay for loading Queue.py.
> b) Queue can be documented with all of the other threading primitives,
> rather than being off somewhere else in its own top-level section.
Do top-level sections have to limit themselves to a single module?
Even if they do, I think it's fine to plant a prominent link to the
Queue module. You can't really expect people to learn how to use
threads wisely from reading the library reference anyway.
> My second problem is with the current signatures of the put() and get()
> methods. Specifically, the following code blocks forever instead of raising an
> Empty exception after 500 milliseconds as one might expect:
> from Queue import Queue
> x = Queue()
I'm not sure if I have much sympathy with a bug due to refusing to
read the docs... :)
> I assume the current signature is there for backward compatibility with the
> original version that didn't support timeouts (considering the difficulty of
> telling the difference between "x.get(1)" and "True = 1; x.get(True)" from
> inside the get() method)
Huh? What a bizarre idea. Why would you do that? I gues I don't
understand where you're coming from.
> However, the need to write "x.get(True, 0.5)" seems seriously redundant, given
> that a single paramater can actually handle all the options (as is currently
> the case with Condition.wait()).
So write x.get(timeout=0.5). That's clear and unambiguous.
> The "put_nowait" and "get_nowait" functions are fine, because they serve a
> useful documentation purpose at the calling point (particularly given the
> current clumsy timeout signature).
> What do people think of the idea of adding "put_wait" and "get_wait" methods
> with the signatures:
-1. I'd rather not tweak the current Queue module at all until Python
3000. Then we could force people to use keyword args.
> Optionally, the existing "put" and "get" methods could be deprecated, with the
> goal of eventually changing their signature to match the put_wait and get_wait
> methods above.
Apart from trying to guess the API without reading the docs (:-), what
are the use cases for using put/get with a timeout? I have a feeling
it's not that common.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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