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. 于 2018年4月16日周一 上午12:53写道：

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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 To: python-ideas 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 wrote:

...

On Sun, Apr 15, 2018 at 05:15:55PM +0300, Alexey Shrub wrote:

...

В Воскресенье, 15 апр. 2018 в 2:40 , Nick Coghlan 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. _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/

---------- Forwarded message ---------- From: Tim Peters To: Raymond Hettinger Cc: Python-Ideas 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 ]

...

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" 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 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 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 To: Antoine Pitrou Cc: Python-Ideas Bcc: Date: Sun, 15 Apr 2018 11:52:49 -0500 Subject: Re: [Python-ideas] A cute Python implementation of itertools.tee [Antoine Pitrou ]

...

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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