Bugs item #1275677, was opened at 2005-08-29 15:49
Message generated for change (Settings changed) made by birkenfeld
You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1275677&group_id=5470
Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Python Interpreter Core
Group: Feature Request
Status: Open
Resolution: None
Priority: 5
Submitted By: Antoine Pitrou (pitrou)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: add a get() method to sets
Initial Comment:
Hi,
I would like to propose a new method for the builtin
set objects. Currently we have a pop() method which
pops an element from the set. What I often need,
though, is a method that gets an arbitrary element
without removing it (because adding / removing stuff is
dealt with in
another part of the program).
Right now the simplest way to do that is :
value = iter(my_set).next()
There are two problems with this:
1. it's ugly and not very intuitive
2. it is not atomic; this means if another thread
updates the set, I can get a "RuntimeError: dictionary
changed size during iteration" (btw, the message is
slightly wrong, it should be "set" instead of "dictionary")
Although the first problem is rather minor (but
annoying nevertheless), the second one is a real
showstopper in some cases - yes, I did encounter it for
real.
There is a way to avoid the second problem :
value = list(my_set)[0]
But of course, not only it is still ugly, but it is
also highly inefficient when the set is big. So in the
end I am forced to use an explicit lock around the
aforementioned construct (value = iter(my_set).next())
as well as around any other piece of code that can
update the set from another thread. This is tedious and
error-prone, and probably a bit inefficient.
So for the bottom line: it would be in some cases very
useful to have an atomic get() method in addition to
the pop() method on sets. (it could probably be applied
to frozensets and dicts too)
The implementation would probably not be very
difficult, since it's the same as pop() with the
removal feature removed. ;) But I'm not familiar with
the Python internals.
What do you think ?
Regards
Antoine.
----------------------------------------------------------------------
You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1275677&group_id=5470
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
