Dear Steve, I'm sorry to annoy you by my proposal, but I do think using
unicode might be wise in current stage.
\triangleq could be print with unicode number \u225c, and adding plugins to
support typing this in editors could be easy, just simply map \xxx to the
specific unicode char when we press the tab after typing it.
People using Julia language are proud of it but I think it's just something
convenient could be used in any other language.
There are other reasons to support unicode but it's out of this topic.
Although ':=' and '->' are not perfect, in the range of ASCII it seems to
be impossible to find a better one.
<python-ideas-request@python.org> 于 2018年4月16日周一 上午12:53写道：
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Today's Topics:
1. Re: Rewriting file - pythonic way (Mahmoud Hashemi)
2. Re: Start argument for itertools.accumulate() [Was: Proposal:
A Reduce-Map Comprehension and a "last" builtin] (Tim Peters)
3. Re: Spelling of Assignment Expressions PEP 572 (was post #4)
(Steven D'Aprano)
4. Re: Rewriting file - pythonic way (Oleg Broytman)
5. Re: A cute Python implementation of itertools.tee (Tim Peters)
---------- Forwarded message ----------
From: Mahmoud Hashemi <mahmoud@hatnote.com>
To: python-ideas <python-ideas@python.org>
Cc:
Bcc:
Date: Sun, 15 Apr 2018 09:10:57 -0700
Subject: Re: [Python-ideas] Rewriting file - pythonic way
Depending on how firm your requirements around locking are, you may find
this code useful:
https://github.com/mahmoud/boltons/blob/6b0721b6aeda6d3ec6f5d31be7c741bc7fcc...
(docs here:
http://boltons.readthedocs.io/en/latest/fileutils.html#atomic-file-saving
)
Basically every operating system has _some_ way of doing an atomic file
replacement, letting us guarantee that a file at a given location is always
valid. atomic_save provides a unified interface to that cross-platform
behavior.
The code does not do locking, as neither I nor its other users have wanted
it, but I'd be happy to extend it if there's a sensible default.
On Sun, Apr 15, 2018 at 8:19 AM, Oleg Broytman <phd@phdru.name> wrote:
On Sun, Apr 15, 2018 at 05:15:55PM +0300, Alexey Shrub <ashrub@yandex.ru>
wrote:
В Воскресенье, 15 апр. 2018 в 2:40 , Nick Coghlan <ncoghlan@gmail.com>
написал:
https://bugs.python.org/issue8604#msg174104 is the relevant tracker
discussion
Thanks all, I agree that universal and absolutly safe solution is very
difficult, but for experiment I made some draft
https://github.com/worldmind/scripts/tree/master/filerewrite
Good!
main code here
https://github.com/worldmind/scripts/blob/master/filerewrite/filerewrite.py#...
Can I recommend to catch exceptions in `backuper.backup()`,
cleanup backuper and unlock locker?
Oleg.
--
Oleg Broytman http://phdru.name/
phd@phdru.name
Programmers don't die, they just GOSUB without RETURN.
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---------- Forwarded message ----------
From: Tim Peters <tim.peters@gmail.com>
To: Raymond Hettinger <raymond.hettinger@gmail.com>
Cc: Python-Ideas <python-ideas@python.org>
Bcc:
Date: Sun, 15 Apr 2018 11:15:18 -0500
Subject: Re: [Python-ideas] Start argument for itertools.accumulate()
[Was: Proposal: A Reduce-Map Comprehension and a "last" builtin]
[Raymond Hettinger <raymond.hettinger@gmail.com>]
Q. Do other languages do it?
A. Numpy, no. R, no. APL, no. Mathematica, no. Haskell, yes.
*
http://docs.scipy.org/doc/numpy/reference/generated/numpy.ufunc.accumulate.h...
*
https://stat.ethz.ch/R-manual/R-devel/library/base/html/cumsum.html
* http://microapl.com/apl/apl_concepts_chapter5.html
\+ 1 2 3 4 5
1 3 6 10 15
* https://reference.wolfram.com/language/ref/Accumulate.html
* https://www.haskell.org/hoogle/?hoogle=mapAccumL
There's also C++, which is pretty much "yes" to every variation
discussed so far:
* partial_sum() is like Python's current accumulate(), including
defaulting to doing addition.
http://en.cppreference.com/w/cpp/algorithm/partial_sum
* inclusive_scan() is also like accumulate(), but allows an optional
"init" argument (which is returned if specified), and there's no
guarantee of "left-to-right" evaluation (it's intended for associative
binary functions, and wants to allow parallelism in the
implementation).
http://en.cppreference.com/w/cpp/algorithm/inclusive_scan
* exclusive_scan() is like inclusive_scan(), but _requires_ an "init"
argument (which is not returned).
http://en.cppreference.com/w/cpp/algorithm/exclusive_scan
* accumulate() is like Python's functools.reduce(), but the operation
is optional and defaults to addition, and an "init" argument is
required.
http://en.cppreference.com/w/cpp/algorithm/accumulate
---------- Forwarded message ----------
From: "Steven D'Aprano" <steve@pearwood.info>
To: python-ideas@python.org
Cc:
Bcc:
Date: Mon, 16 Apr 2018 02:15:59 +1000
Subject: Re: [Python-ideas] Spelling of Assignment Expressions PEP 572
(was post #4)
On Sun, Apr 15, 2018 at 11:11:37PM +0800, Thautwarm Zhao wrote:
I think maybe we can use unicode characters like ≜ (\triangleq) and add
the
support of unicode completion to python repl. The unicode completion of
editors or ides has been quite mature.
What key combination do I need to type to get ≜ in the following editors
please? I tried typing \triangleq but all I got was \triangleq.
Notepad (Windows)
Brackets (Mac)
BBEdit (Mac)
kwrite (Linux)
kate
nano
geany
gedit
as well as IDLE, my mail client (kmail, Thunderbird or mutt), my web
browsers (Firefox, Opera and Chromium), the interactive interpreter in
various different consoles, my Usenet client (Pan and KNode) and IRC
(pidgin).
Oh, having it work in LibreOffice and GoogleApps too would be nice,
although not essential since I don't often write code in them.
And what decent fonts do I need to install for ≜ to show up as something
other than a square box ("missing glyph")?
--
Steve
---------- Forwarded message ----------
From: Oleg Broytman <phd@phdru.name>
To: python-ideas@python.org
Cc:
Bcc:
Date: Sun, 15 Apr 2018 18:49:16 +0200
Subject: Re: [Python-ideas] Rewriting file - pythonic way
On Sun, Apr 15, 2018 at 09:10:57AM -0700, Mahmoud Hashemi <
mahmoud@hatnote.com> wrote:
Depending on how firm your requirements around locking are, you may find
this code useful:
https://github.com/mahmoud/boltons/blob/6b0721b6aeda6d3ec6f5d31be7c741bc7fcc...
(docs here:
http://boltons.readthedocs.io/en/latest/fileutils.html#atomic-file-saving
)
Basically every operating system has _some_ way of doing an atomic file
replacement, letting us guarantee that a file at a given location is
always
valid. atomic_save provides a unified interface to that cross-platform
behavior.
The code does not do locking, as neither I nor its other users have
wanted
it, but I'd be happy to extend it if there's a sensible default.
I don't like it renames the file at the end. Renaming could lead to
changed file ownership and permissions; restoring permissions is not
always possible, restoring ownership is almost never possible. Renaming
is also not always possible due to restricted directory permissions.
On Sun, Apr 15, 2018 at 8:19 AM, Oleg Broytman <phd@phdru.name> wrote:
В Воскресенье, 15 апр. 2018 в 2:40 , Nick Coghlan <
ncoghlan@gmail.com>
написал:
https://bugs.python.org/issue8604#msg174104 is the relevant
On Sun, Apr 15, 2018 at 05:15:55PM +0300, Alexey Shrub <
ashrub@yandex.ru>
wrote:
tracker
discussion
Thanks all, I agree that universal and absolutly safe solution is
very
difficult, but for experiment I made some draft
https://github.com/worldmind/scripts/tree/master/filerewrite
Good!
main code here
https://github.com/worldmind/scripts/blob/master/
filerewrite/filerewrite.py#L46
Can I recommend to catch exceptions in `backuper.backup()`,
cleanup backuper and unlock locker?
Oleg.
--
Oleg Broytman http://phdru.name/ phd@phdru.name
Programmers don't die, they just GOSUB without RETURN.
---------- Forwarded message ----------
From: Tim Peters <tim.peters@gmail.com>
To: Antoine Pitrou <solipsis@pitrou.net>
Cc: Python-Ideas <python-ideas@python.org>
Bcc:
Date: Sun, 15 Apr 2018 11:52:49 -0500
Subject: Re: [Python-ideas] A cute Python implementation of itertools.tee
[Antoine Pitrou <solipsis@pitrou.net>]
This implementation doesn't work with Python 3.7 or 3.8.
I've tried it here:
https://gist.github.com/pitrou/b3991f638300edb6d06b5be23a4c66d6
and get:
Traceback (most recent call last):
File "mytee.py", line 14, in gen
mylast = last[1] = last = [next(it), None]
StopIteration
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "mytee.py", line 47, in <module>
run(mytee1)
File "mytee.py", line 36, in run
lists[i].append(next(iters[i]))
RuntimeError: generator raised StopIteration
(Yuck!)
Thanks for trying! I wonder whether that will break other code. I
wrote PEP 255, and this part was intentional at the time:
"""
If an unhandled exception-- including, but not limited to,
StopIteration --is raised by, OR PASSES THROUGH [emphasis added], a
generator function, then the exception is passed on to the caller in
the usual way, and subsequent attempts to resume the generator
function raise StopIteration.
"""
I've exploited that a number of times.
In short, you want the following instead:
try:
mylast = last[1] = last = [next(it), None]
except StopIteration:
return
No, I don't ;-) If I have to catch StopIteration myself now, then I
want the entire "white True:" loop in the "try" block. Setting up
try/except machinery anew on each iteration would add significant
overhead; doing it just once per derived generator wouldn't.
def mytee(xs, n):
last = [None, None]
def gen(it, mylast):
nonlocal last
while True:
mylast = mylast[1]
if not mylast:
mylast = last[1] = last = [next(it), None]
That's smart and obscure :-o
The way it works is that the `last` assignment changes the `last` value
seen by all derived generators, while the `last[1]` assignment updates
the bindings made in the other generators' `mylast` lists... It's
difficult to find the words to explain it.
Which is why I didn't even try - I did warn people that if they
thought it "was obvious", they hadn't yet thought hard enough ;-)
Good job!
The chained assignment makes it more difficult to parse as well (when I
read this I don't know if `last[i]` or `last` gets assigned first;
apparently the answer is `last[i]`, otherwise the recipe wouldn't work
correctly).
Ya, I had to look it up too :-) Although, like almost everything else
in Python, chained assignments proceed "left to right". I was just
trying to make it as short as possible, to increase the "huh - can
something that tiny really work?!" healthy skepticism factor :-)
Perhaps like this:
while True:
mylast = mylast[1]
if not mylast:
try:
# Create new list link
mylast = [next(it), None]
except StopIteration:
return
else:
# Append to other generators `mylast` linked lists
last[1] = mylast
# Update shared list link
last = last[1]
yield mylast[0]
I certainly agree that's easier to follow. But that wasn't really the
point ;-)
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Chris Angelico
Thautwarm Zhao