Right now, the following code is valid in Python 3.9 (and infinitely loops):
```
lst = [1, 2, 3]
for i in lst:
lst.append(i)
```
IMO this is a source of bugs, and even though this behavior is technically
documented (https://bugs.python.org/issue32767), I don't know if it should
belong in th
09.10.21 01:24, Tyler Hou via Python-ideas пише:
> Concretely, I'm proposing the following set of changes to Python:
>
> 1. If the size of a list, set, or dict changes, invalidate all existing
> iterators to that containers. Document this behavior as part of the public
> API.
> 2. Attempting to
Christopher Barker writes:
> But last time, one of the use cases was "get [an arbitrary] item
> from a dict", and there really is not a terribly easy (and
> efficient) way to do that now.
What's wrong with thedict.popitem()? Works in Python 2.7, BTW.
Granted, this doesn't help for a random i
Deleting is quite error prone, but appending during iteration is very useful in
implementing an iterative form of recursive algorithms. It effectively gives a
FIFO queue which remembers all items after you're done. In general the
behaviour of a list iterator can be understood completely if you e
On Sun, Oct 10, 2021 at 01:51:52AM +0900, Stephen J. Turnbull wrote:
> Christopher Barker writes:
>
> > But last time, one of the use cases was "get [an arbitrary] item
> > from a dict", and there really is not a terribly easy (and
> > efficient) way to do that now.
>
> What's wrong with thedi
On 9/10/21 11:24 am, Tyler Hou via Python-ideas wrote:
Right now, the following code is valid in Python 3.9 (and infinitely loops):
```
lst = [1, 2, 3]
for i in lst:
lst.append(i)
```
1. If the size of a list, set, or dict changes, invalidate all existing
iterators to that containers.
T
Is this behavior of list iteration guaranteed by documentation
anywhere? A quick search didn't yield any results for me.
If not, I suggest either:
a) it gets documented so developers can rely on it, or
b) the lack of guarantee is documented so that we can reserve a change
of behavior later.
Paul
Hello all,
I was thinking about the following idioms:
__version__ = "1.0"
import sys
if sys.version_info < (3, 6):
# Yell at the user
I feel like there could be a better way to define versions. There's no real
standard way to specify versions in Python, other than "use semantic
versionin
On Fri, Oct 08, 2021 at 01:42:35PM -0700, Christopher Barker wrote:
> It really ius frustrating how often we repeat entire conversations on this
> list :-(
That's because y'all don't just admit I'm right the first time *wink*
> But last time, one of the use cases was "get a random item from a d
I've known and relied on the behavior since Python 1.4. I mean, not often,
but it's been consistent.
In the case where I want to loop over what the loop was at start, rather
than what it might become, a slice comes in handy:
for item in mylist[:]:
# do stuff, maybe mutate list
On Sat, Oct 9
On Sat, Oct 9, 2021, 10:44 PM Steven D'Aprano
> Apart from a programming exercise and teaching moment, why would you want
> to get a random key and value from a dict? In 25-ish years of using Python,
> I think that the number of times I've needed to do that is zero. A random
> item from a list, do
There is a Version type in the packaging package that imjments the
“official” versioning scheme for PyPI packages.
https://packaging.pypa.io/en/latest/index.html#
Should it be in the stdlib? Maybe, I think it has used casss beyond pip and
friends.
I’ve actually written my own more limited vers
As was discussed the last time, I don’t know that selecting a random item
from a dict has a lot of use cases — I’m pretty sure the only time I’ve
needed to do it was for Dave Thomas’s “trigrams” coding kata. Though I’m
not sure I’ve used random.choice fir anything mor “real” either.
But it is a mo
On Fri, Oct 08, 2021 at 01:42:35PM -0700, Christopher Barker wrote:
> Anyway, I do see the benefit of adding first() to itertools -- there really
> is a key problem with:
>
> next(iter(an_iterable))
>
> for newbies -- you can get really really far in Python without ever having
> to call either
On Sat, Oct 9, 2021, 9:56 PM Steven D'Aprano wrote:
> [Snip...]
Newbies won't know first() lives in itertools, and those experienced
> enough to know it is there probably won't bother to use it.
>
A very good point.
Let's get back to the original topic. Should `dict.items()` be indexable
now
On Wed, Oct 06, 2021 at 03:42:28PM +0100, Alex Waygood wrote:
> > Whether they are added to dict or itertools, there are still nine of
> > them
>
> No, the suggestion was to add two functions to itertools (first() and
> last(), which would work with any iterable, not just dicts), rather
> than
On Sun, Oct 10, 2021 at 3:05 PM Finn Mason wrote:
>
> On Sat, Oct 9, 2021, 9:56 PM Steven D'Aprano wrote:
>>
>> [Snip...]
>
>
>> Newbies won't know first() lives in itertools, and those experienced
>> enough to know it is there probably won't bother to use it.
>
>
> A very good point.
>
> Let's g
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