subject:"\[Python\-ideas\] Re\: New feature"

On Fri, Oct 16, 2020, 10:43 PM Steven D'Aprano

> > What manner of savages run a terminal without a multiplexer? :-)
>

I understand using screen or tmux when ssh'ing into a remote machine, but
> what advantage are they when you are using the local machine via a GUI?
>

It was definitely persistent SSH sessions that first got me hooked on
screen, later tmux. I've played around with mosh, but it hasn't entirely
played nice with other aspects of my workflow.

But even purely locally, tmux lets me nohup services (e.g. a flask server
I'm working on) without them dying if terminal closes. Reattaching to the
window the server runs in is simple. And with tmux- resurrect, I can
save/restore the state of the panes I use on restart. A resurrect even
relaunches some applications like htop and vim, and at least puts panes in
the saved PWD if not.

All that said, the folks who want a beginner friendly os.clear() are
probably not ones who tweak tmux plugins and key bindings.
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[Python-ideas] Re: New feature

On Fri, Oct 16, 2020 at 10:28:20PM -0400, David Mertz wrote:
> On Fri, Oct 16, 2020, 10:16 PM Steven D'Aprano
> 
> > I think that if we go ahead with this, we shouldn't allow lack
> > of support for screen and/or tmux to stand in the way. A 99% solution is
> > better than a 0% solution :-)
> >
> 
> What manner of savages run a terminal without a multiplexer? :-)

Savages with a terminal that natively supports multiple tabs, and a GUI 
desktop environment that supports multiple terminal windows :-P

I understand using screen or tmux when ssh'ing into a remote machine, 
but what advantage are they when you are using the local machine via a 
GUI?


-- 
Steve
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[Python-ideas] Re: New feature

On Fri, Oct 16, 2020, 10:16 PM Steven D'Aprano

> I think that if we go ahead with this, we shouldn't allow lack
> of support for screen and/or tmux to stand in the way. A 99% solution is
> better than a 0% solution :-)
>

What manner of savages run a terminal without a multiplexer? :-)
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[Python-ideas] Re: New feature

On Fri, Oct 16, 2020 at 09:53:35PM -0400, David Mertz wrote:
> On Fri, Oct 16, 2020 at 9:36 PM Steven D'Aprano  wrote:
> 
> > > Well, in terminals like bash, `clear` does not really delete the
> > > previous input. It simply move the scroll so the first line of the
> > > input is the current input.
> >
> > That's not actually correct: in bash, `clear` actually deletes the
> > scrollback buffer too.
> >
> 
> I never noticed that, since my "terminal" is `tmux` (running inside a Linux
> terminal).  In that case, `clear` might clear the underlying terminal
> scrollback buffer, but it does not clear the tmux scrollback buffer.  The
> `screen` terminal multiplexer is similar.

Oh yeah; I forgot about screen and tmux.

I just tried it in screen, and `os.system('clear')` does not clear the 
scrollback used by screen.

I think that if we go ahead with this, we shouldn't allow lack 
of support for screen and/or tmux to stand in the way. A 99% 
solution is better than a 0% solution :-)


> All of which suggests to me that doing the "same thing" in a platform
> neutral way is not an insignificant effort.

Indeed.



-- 
Steve
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[Python-ideas] Re: New feature

On Fri, Oct 16, 2020 at 9:36 PM Steven D'Aprano  wrote:

> > Well, in terminals like bash, `clear` does not really delete the
> > previous input. It simply move the scroll so the first line of the
> > input is the current input.
>
> That's not actually correct: in bash, `clear` actually deletes the
> scrollback buffer too.
>

I never noticed that, since my "terminal" is `tmux` (running inside a Linux
terminal).  In that case, `clear` might clear the underlying terminal
scrollback buffer, but it does not clear the tmux scrollback buffer.  The
`screen` terminal multiplexer is similar.  Both screen and tmux HAVE a way
to clear their scrollback buffer, but it is two different ways between
those popular programs... both different from the `clear` command in the
underlying terminal.

I don't use MacOS anymore, but when I did I used iTerm2, which has a fork
of the tmux code to implement its pane division functionality.  I do not
know whether that very popular terminal clears the actual scrollback with
the `clear` command.  I feel like I remember it not doing that, but it's
been a couple years.

All of which suggests to me that doing the "same thing" in a platform
neutral way is not an insignificant effort.

-- 
The dead increasingly dominate and strangle both the living and the
not-yet born.  Vampiric capital and undead corporate persons abuse
the lives and control the thoughts of homo faber. Ideas, once born,
become abortifacients against new conceptions.
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[Python-ideas] Re: New feature

On Fri, Oct 16, 2020 at 11:30:56PM +0200, Marco Sulla wrote:

> Well, in terminals like bash, `clear` does not really delete the
> previous input. It simply move the scroll so the first line of the
> input is the current input.

That's not actually correct: in bash, `clear` actually deletes the 
scrollback buffer too.

In modern Linuxes, `clear` takes an option `-x` which suppresses that 
behaviour. Perhaps you have an alias?

alias clear='clear -x'



-- 
Steve
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[Python-ideas] Re: New feature

On Sat, Oct 17, 2020 at 05:44:12AM +1100, Chris Angelico wrote:
> On Sat, Oct 17, 2020 at 5:40 AM Jonathan Crall  wrote:
> >
> > I just want to point out that I can think of a valid use case for `clf`. 
> > I'm not sure if it was mentioned.
> >
> > In the case where you have a script that produces a lot of output, a common 
> > task might be scrolling to the beginning to check an output. If your screen 
> > was not fresh, and you had a lot of previous output (say from running the 
> > script multiple times), then it is hard to find the beginning unless you 
> > have previously cleared the screen.
> >
> 
> This is exactly why I think this should NOT be made too easy. That's a
> perfect example of an attractive nuisance: instead of creating a
> divider (say, a half a dozen blank lines, or a row of hyphens with a
> blank or two each side), you're throwing away all information from the
> previous output, making it impossible to compare the two.

Why are we assuming that our "clear screen" command flushes the 
scrollback buffer as well as clearing the screen?

I do not want any cls command to flush the scrollback buffer by default 
(although I wouldn't object to an option to do so). I would want it to 
be more like ^L although that's probably dependent on your terminal.

In other words, I want the default to be like the command `clear -x` 
(bash), not `clear`. I also like the idea given here:

https://askubuntu.com/a/997893

of printing a divider first so that when scrolling back the clear screen 
is obvious.

So here's my first attempt (untested!) of a "cls" pseudo-builtin 
command, similar to the help and quit builtins added by site.py. It 
assumes that os.clear exists and takes an appropriate optional flag.

```
import builtins
import os

class ScreenClearer:
if os.name == 'posix':
def __repr__(self):
return 'Use cls() or Ctrl-L to clear the screen.'
else:
 def __repr__(self):
return 'Use cls() to clear the screen.'
def __call__(self, flush_scrollback=False):
print('\n', '-'*os.get_terminal_size()[0], '\n', sep='')
os.clear(flush_scrollback)

builtins.cls = ScreenClearer()
```

Of course I'm glossing over the hard part -- actually clearing the 
screen and/or scrollback.

I think that doing both is easy:

- on Windows: `os.system('cls')`

- on Posix: `os.system('clear')`

To *not* clear the scrollback is easy on modern Linuxes:

- `os.system('clear -x')`

but I don't know how you can recognise in advance whether it is 
supported or not. On terminals that support it, this should work:

- `print('\33[H\33[2J')`

but I have no idea how to avoid clearing the scrollback buffer on 
Windows, or other posix systems with unusual terminals.

Of course IDLE will require something different.

The ultimate fallback for clearing the visible screen but not the 
scrollback is just `print('\n'*os.get_terminal_size()[1])`.

So we have plenty of solutions for this, but none of them are platform 
independent, and picking the right option for your specific terminal may 
be tricky for the more unusual terminals.

I don't have access to a Windows machine to experiment, but I found 
these issues which may be relevant:

https://github.com/microsoft/terminal/issues/1305

https://github.com/microsoft/terminal/issues/1882

-- 
Steve
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[Python-ideas] Re: New feature

2020-10-16 Thread Marco Sulla

Well, in terminals like bash, `clear` does not really delete the
previous input. It simply move the scroll so the first line of the
input is the current input.

Maybe the REPL can emulate this in some way.
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[Python-ideas] Re: New feature

2020-10-16 Thread Ethan Furman


On 10/13/20 4:46 PM, Steven D'Aprano wrote:


And I [clear my screen] frequently, in both Python and bash. Because I never
remember the name of the bash command to do it (cls or clear?), and
Python doesn't have one, I just hold down the Enter key for a couple of
seconds until there's no clutter visible.


I use `reset` -- particularly handy when you cat a binary file.

--
~Ethan~
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[Python-ideas] Re: New feature

2020-10-16 Thread Jonathan Crall

@Paul Moor, I agree with you. Personally, I'd rather not use it, and if it
was used in an importable module I'd claim it was bad practice.

But in general I don't think there is a right answer of if you *should *or
not. I think it is valid for personal preferences to vary here. If this is
something someone forgets to do a lot (and everyone has their own personal
quirks about what's hard/easy for them to remember), then it could be
annoying to the point where this feature could really help them.

But yes, in most cases I'd rather not use it, and I would get peeved if
someone's code they advertised as reusable used this (but then again I also
get peeved when people execute print statements at import time).



On Fri, Oct 16, 2020 at 5:02 PM Paul Moore  wrote:

> On Fri, 16 Oct 2020 at 20:43, Jonathan Crall  wrote:
> >
> > @Chris Angelico If you are more application focused, or trying to get a
> scientific result, and you don't care too much about the reusability of
> your scripts, then I can see the validity of this use case. But I would not
> want to install a module on pypi that made use of this. From a software
> perspective this is 100% bad practice, but from a practitioner perspective
> --- and there are a lot of practitioners that only use Python as a tool
> (like a DSL) --- I can see wanting it.
> >
> > So, that's the question: does the Python stdlib want to let you do this?
> Will the number of software engineers who use this incorrectly outweigh the
> number of people who seem to want this for a valid reason? I'm not sure
> what the answer is.
> >
> > FWIW executing `print('\x1b[H\x1b[2J\x1b[3J')` in my IPython terminal
> cleared the screen.
>
> Why would you want to put this in your script, so that you have no
> choice (short of editing the script) as to whether it happens? Surely
> better to clear your terminal from the command prompt *before* running
> your script? Yes, you can forget, but I'd rather forget occasionally
> than lose essential data because I ran a script that I'd forgotten has
> an os.clear() at the top...
>
> I suspect Guido's right, it's asked for often enough, and fiddly
> enough to write, that adding it is a net gain. But I'd be very
> unlikely to use it myself, and I'd strongly advise people against
> using it if asked.
>
> Paul
>


-- 
-Dr. Jon Crall (him)
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[Python-ideas] Re: New feature




On 16/10/2020 22:02, Paul Moore wrote:

On Fri, 16 Oct 2020 at 20:43, Jonathan Crall  wrote:

@Chris Angelico If you are more application focused, or trying to get a 
scientific result, and you don't care too much about the reusability of your 
scripts, then I can see the validity of this use case. But I would not want to 
install a module on pypi that made use of this. From a software perspective 
this is 100% bad practice, but from a practitioner perspective --- and there 
are a lot of practitioners that only use Python as a tool (like a DSL) --- I 
can see wanting it.

So, that's the question: does the Python stdlib want to let you do this? Will 
the number of software engineers who use this incorrectly outweigh the number 
of people who seem to want this for a valid reason? I'm not sure what the 
answer is.


Why is this the question?  Any feature can be misused.  That some users 
will misuse it is not IMHO a reason to deprive those users who will use 
it correctly.

Best wishes
Rob Cliffe
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[Python-ideas] Re: New feature

2020-10-16 Thread Paul Moore

On Fri, 16 Oct 2020 at 20:43, Jonathan Crall  wrote:
>
> @Chris Angelico If you are more application focused, or trying to get a 
> scientific result, and you don't care too much about the reusability of your 
> scripts, then I can see the validity of this use case. But I would not want 
> to install a module on pypi that made use of this. From a software 
> perspective this is 100% bad practice, but from a practitioner perspective 
> --- and there are a lot of practitioners that only use Python as a tool (like 
> a DSL) --- I can see wanting it.
>
> So, that's the question: does the Python stdlib want to let you do this? Will 
> the number of software engineers who use this incorrectly outweigh the number 
> of people who seem to want this for a valid reason? I'm not sure what the 
> answer is.
>
> FWIW executing `print('\x1b[H\x1b[2J\x1b[3J')` in my IPython terminal cleared 
> the screen.

Why would you want to put this in your script, so that you have no
choice (short of editing the script) as to whether it happens? Surely
better to clear your terminal from the command prompt *before* running
your script? Yes, you can forget, but I'd rather forget occasionally
than lose essential data because I ran a script that I'd forgotten has
an os.clear() at the top...

I suspect Guido's right, it's asked for often enough, and fiddly
enough to write, that adding it is a net gain. But I'd be very
unlikely to use it myself, and I'd strongly advise people against
using it if asked.

Paul
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[Python-ideas] Re: New feature

2020-10-16 Thread Jonathan Crall

@Chris Angelico  If you are more application focused, or
trying to get a scientific result, and you don't care too much about the
reusability of your scripts, then I can see the validity of this use case.
But I would not want to install a module on pypi that made use of this.
>From a software perspective this is 100% bad practice, but from a
practitioner perspective --- and there are a lot of practitioners that only
use Python as a tool (like a DSL) --- I can see wanting it.

So, that's the question: does the Python stdlib want to let you do this?
Will the number of software engineers who use this incorrectly outweigh the
number of people who seem to want this for a valid reason? I'm not sure
what the answer is.

FWIW executing `print('\x1b[H\x1b[2J\x1b[3J')` in my IPython terminal
cleared the screen.

On Fri, Oct 16, 2020 at 2:45 PM Chris Angelico  wrote:

> On Sat, Oct 17, 2020 at 5:40 AM Jonathan Crall  wrote:
> >
> > I just want to point out that I can think of a valid use case for `clf`.
> I'm not sure if it was mentioned.
> >
> > In the case where you have a script that produces a lot of output, a
> common task might be scrolling to the beginning to check an output. If your
> screen was not fresh, and you had a lot of previous output (say from
> running the script multiple times), then it is hard to find the beginning
> unless you have previously cleared the screen.
> >
>
> This is exactly why I think this should NOT be made too easy. That's a
> perfect example of an attractive nuisance: instead of creating a
> divider (say, a half a dozen blank lines, or a row of hyphens with a
> blank or two each side), you're throwing away all information from the
> previous output, making it impossible to compare the two. Once your
> script has a clear-screen at the start of it, you lose the option to
> examine history, whereas a simple few blank lines would have a similar
> effect without losing anything.
>
> If it is added to the stdlib, I hope that it's buried away where
> people find it only if they're actually looking for it. There ARE
> valid use-cases, but there are far far more cases where it shouldn't
> be used.
>
> ChrisA
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-- 
-Dr. Jon Crall (him)
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[Python-ideas] Re: New feature

2020-10-16 Thread Chris Angelico

On Sat, Oct 17, 2020 at 5:40 AM Jonathan Crall  wrote:
>
> I just want to point out that I can think of a valid use case for `clf`. I'm 
> not sure if it was mentioned.
>
> In the case where you have a script that produces a lot of output, a common 
> task might be scrolling to the beginning to check an output. If your screen 
> was not fresh, and you had a lot of previous output (say from running the 
> script multiple times), then it is hard to find the beginning unless you have 
> previously cleared the screen.
>

This is exactly why I think this should NOT be made too easy. That's a
perfect example of an attractive nuisance: instead of creating a
divider (say, a half a dozen blank lines, or a row of hyphens with a
blank or two each side), you're throwing away all information from the
previous output, making it impossible to compare the two. Once your
script has a clear-screen at the start of it, you lose the option to
examine history, whereas a simple few blank lines would have a similar
effect without losing anything.

If it is added to the stdlib, I hope that it's buried away where
people find it only if they're actually looking for it. There ARE
valid use-cases, but there are far far more cases where it shouldn't
be used.

ChrisA
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[Python-ideas] Re: New feature

2020-10-16 Thread Jonathan Crall

I just want to point out that I can think of a valid use case for `clf`.
I'm not sure if it was mentioned.

In the case where you have a script that produces a lot of output, a common
task might be scrolling to the beginning to check an output. If your screen
was not fresh, and you had a lot of previous output (say from running the
script multiple times), then it is hard to find the beginning unless you
have previously cleared the screen.

If you have cls, you can ensure that your big crazy
undergrad-programming-level script always clears the screen when it runs.
Maybe that helps you get your homework in on time. There is a task you
commonly do (clear the screen via cls or clear) programatically in python.

You may say: why are you not using logging? Well, perhaps --- because it
seems it is typically students who want to do this --- perhaps they don't
know how to do logging, or have doubts that they know how to do it
properly.

It seems that something like this might be better as a third party library,
given that it's more of a stdout + console specific thing. But on the other
hand this isn't much worse than `os.startfile` on windows.



On Fri, Oct 16, 2020 at 1:21 PM David Mertz  wrote:

> I agree with Guido here.  Although I really don't care about the
> capability myself, it feels like enough people do want a "clear screen"
> function... and from the discussion, in feels like there are a LOT of
> variations in how to do it across different operating systems, OS versions,
> terminals, shells, etc.
>
> Having a common interface of `os.clear()` that did whatever funny thing a
> particular environment needed would save some folks trouble.  Of course,
> I'm not certain how far it is possible to auto-detect the environment
> details within that function to "do the right thing" ... but probably there
> are clever hacks that get to 90% working.
>
> On Fri, Oct 16, 2020 at 1:03 PM Rob Cliffe via Python-ideas <
> python-ideas@python.org> wrote:
>
>>
>>
>> On 16/10/2020 13:55, Chris Angelico wrote:
>> > On Fri, Oct 16, 2020 at 11:08 PM Rob Cliffe 
>> wrote:
>> >>
>> >>
>> >> On 16/10/2020 11:59, Chris Angelico wrote:
>> >>> On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
>> >>>  wrote:
>> 
>>  On 13/10/2020 23:35, Guido van Rossum wrote:
>> > Can one of the educators on the list explain why this is such a
>> > commonly required feature? I literally never feel the need to clear
>> my
>> > screen -- but I've seen this requested quite a few times in various
>> > forms, often as a bug report "IDLE does not support CLS". I presume
>> > that this is a common thing in other programming environments for
>> > beginners -- even C++ (given that it was mentioned). Maybe it's a
>> > thing that command-line users on Windows are told to do frequently?
>> > What am I missing that students want to do frequently? Is it a
>> > holdover from the DOS age?
>> >
>>  Sometimes I want a program that displays (more than 1 line of)
>> real-time
>>  information in a Windows CMD box and refreshes it every few seconds
>>  (e.g. progress displays, monitoring open
>>  files/locks/connections/downloads etc.).  It is natural to clear the
>>  screen and display the updated information.
>> >>> Natural perhaps, but ugly. Much better to reposition the cursor and
>> >>> overwrite the previous text, with "clear to end of line" as required;
>> >>> that way, you avoid flicker.
>> >>>
>> >>> C
>> >> I do precisely that in many of my programs for e.g. single-line
>> progress
>> >> displays.
>> >> But for multi-line output I don't know of any way to move the cursor
>> >> back up.
>> >> I work in Windows 10.
>> > Try \x1b[A to move up a line, should work.
>> >
>> > ChrisA
>> Thanks Chris, but no luck.  It just echoes it, with the \x1b (Escape)
>> echoed as a character that looks like a question mark inside a box.
>> Earlier I did try googling for ways of moving the cursor, but almost all
>> I found was ways of moving the *mouse* cursor, and the rest was
>> irrelevant.
>> Rob Cliffe
>> > ___
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>
>
> --
> The dead increasingly dominate and st

[Python-ideas] Re: New feature

I agree with Guido here.  Although I really don't care about the capability
myself, it feels like enough people do want a "clear screen" function...
and from the discussion, in feels like there are a LOT of variations in how
to do it across different operating systems, OS versions, terminals,
shells, etc.

Having a common interface of `os.clear()` that did whatever funny thing a
particular environment needed would save some folks trouble.  Of course,
I'm not certain how far it is possible to auto-detect the environment
details within that function to "do the right thing" ... but probably there
are clever hacks that get to 90% working.

On Fri, Oct 16, 2020 at 1:03 PM Rob Cliffe via Python-ideas <
python-ideas@python.org> wrote:

>
>
> On 16/10/2020 13:55, Chris Angelico wrote:
> > On Fri, Oct 16, 2020 at 11:08 PM Rob Cliffe 
> wrote:
> >>
> >>
> >> On 16/10/2020 11:59, Chris Angelico wrote:
> >>> On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
> >>>  wrote:
> 
>  On 13/10/2020 23:35, Guido van Rossum wrote:
> > Can one of the educators on the list explain why this is such a
> > commonly required feature? I literally never feel the need to clear
> my
> > screen -- but I've seen this requested quite a few times in various
> > forms, often as a bug report "IDLE does not support CLS". I presume
> > that this is a common thing in other programming environments for
> > beginners -- even C++ (given that it was mentioned). Maybe it's a
> > thing that command-line users on Windows are told to do frequently?
> > What am I missing that students want to do frequently? Is it a
> > holdover from the DOS age?
> >
>  Sometimes I want a program that displays (more than 1 line of)
> real-time
>  information in a Windows CMD box and refreshes it every few seconds
>  (e.g. progress displays, monitoring open
>  files/locks/connections/downloads etc.).  It is natural to clear the
>  screen and display the updated information.
> >>> Natural perhaps, but ugly. Much better to reposition the cursor and
> >>> overwrite the previous text, with "clear to end of line" as required;
> >>> that way, you avoid flicker.
> >>>
> >>> C
> >> I do precisely that in many of my programs for e.g. single-line progress
> >> displays.
> >> But for multi-line output I don't know of any way to move the cursor
> >> back up.
> >> I work in Windows 10.
> > Try \x1b[A to move up a line, should work.
> >
> > ChrisA
> Thanks Chris, but no luck.  It just echoes it, with the \x1b (Escape)
> echoed as a character that looks like a question mark inside a box.
> Earlier I did try googling for ways of moving the cursor, but almost all
> I found was ways of moving the *mouse* cursor, and the rest was irrelevant.
> Rob Cliffe
> > ___
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-- 
The dead increasingly dominate and strangle both the living and the
not-yet born.  Vampiric capital and undead corporate persons abuse
the lives and control the thoughts of homo faber. Ideas, once born,
become abortifacients against new conceptions.
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[Python-ideas] Re: New feature

On 16/10/2020 13:55, Chris Angelico wrote:

On Fri, Oct 16, 2020 at 11:08 PM Rob Cliffe wrote:

On 16/10/2020 11:59, Chris Angelico wrote:

On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
wrote:

On 13/10/2020 23:35, Guido van Rossum wrote:

Can one of the educators on the list explain why this is such a
commonly required feature? I literally never feel the need to clear my
screen -- but I've seen this requested quite a few times in various
forms, often as a bug report "IDLE does not support CLS". I presume
that this is a common thing in other programming environments for
beginners -- even C++ (given that it was mentioned). Maybe it's a
thing that command-line users on Windows are told to do frequently?
What am I missing that students want to do frequently? Is it a
holdover from the DOS age?

Sometimes I want a program that displays (more than 1 line of) real-time
information in a Windows CMD box and refreshes it every few seconds
(e.g. progress displays, monitoring open
files/locks/connections/downloads etc.). It is natural to clear the
screen and display the updated information.

Natural perhaps, but ugly. Much better to reposition the cursor and
overwrite the previous text, with "clear to end of line" as required;
that way, you avoid flicker.

I do precisely that in many of my programs for e.g. single-line progress
displays.
But for multi-line output I don't know of any way to move the cursor
back up.
I work in Windows 10.

Try \x1b[A to move up a line, should work.

ChrisA
Thanks Chris, but no luck. It just echoes it, with the \x1b (Escape)
echoed as a character that looks like a question mark inside a box.
Earlier I did try googling for ways of moving the cursor, but almost all
I found was ways of moving the *mouse* cursor, and the rest was irrelevant.

Rob Cliffe

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[Python-ideas] Re: New feature

2020-10-16 Thread Eryk Sun

On 10/16/20, Barry Scott  wrote:
>
> I find that you have to do this to turn on ANSI processing in CMD.EXE on
> Window 10 and I assume earlier Windwows as wel:

You mean the console-session host (conhost.exe). This has nothing to
do with the CMD shell. People often confuse CLI shells (CMD,
PowerShell, bash) with the console/terminal that they use for standard
I/O.

Virtual Terminal mode is supported by the new console in Windows 10 --
not in earlier versions of Windows and not with the legacy console in
Windows 10. If you need to support ANSI sequences with the legacy
console host, consider using a third-party library such as colorama.

You can enable VT mode by default for regular console sessions (i.e.
not headless sessions such as under Windows Terminal, for which it's
always enabled) by setting a DWORD value of 1 named
"VirtualTerminalLevel" in the registry key "HKCU\Console".

> import ctypes
> kernel32 = ctypes.windll.kernel32
> # turn on the console ANSI colour handling
> kernel32.SetConsoleMode( kernel32.GetStdHandle( -11 ), 7 )

You should enable the flag in the current mode value and implement
error handling:

import ctypes
kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)

STD_OUTPUT_HANDLE = -11
ENABLE_VIRTUAL_TERMINAL_PROCESSING = 4
INVALID_HANDLE_VALUE = ctypes.c_void_p(-1).value

kernel32.GetStdHandle.restype = ctypes.c_void_p

hstdout = kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
if hstdout == INVALID_HANDLE_VALUE:
raise ctypes.WinError(ctypes.get_last_error())

mode = ctypes.c_ulong()
if not kernel32.GetConsoleMode(hstdout, ctypes.byref(mode)):
raise ctypes.WinError(ctypes.get_last_error())

mode.value |= ENABLE_VIRTUAL_TERMINAL_PROCESSING
if not kernel32.SetConsoleMode(hstdout, mode):
raise ctypes.WinError(ctypes.get_last_error())
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[Python-ideas] Re: New feature

2020-10-16 Thread Barry Scott




> On 16 Oct 2020, at 14:44, Rob Cliffe via Python-ideas 
>  wrote:
> 
> 
> 
> On 16/10/2020 13:55, Chris Angelico wrote:
>> 
>>> I do precisely that in many of my programs for e.g. single-line progress
>>> displays.
>>> But for multi-line output I don't know of any way to move the cursor
>>> back up.
>>> I work in Windows 10.
>> Try \x1b[A to move up a line, should work.

I find that you have to do this to turn on ANSI processing in CMD.EXE on Window 
10
and I assume earlier Windwows as wel:

import ctypes
kernel32 = ctypes.windll.kernel32
# turn on the console ANSI colour handling
kernel32.SetConsoleMode( kernel32.GetStdHandle( -11 ), 7 )

Now you can use escape sequences:

print('\x1b[31m Hello in red \x1b[m')

Given the need to call WIN32 APIs to get this working making this part
of stdlib would help a lot.

Barry


>> 
>> ChrisA
> Got it working!  The answer is
>  \x1b[1A
> Thanks for the pointer!
> Rob Cliffe
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[Python-ideas] Re: New feature




On 16/10/2020 13:55, Chris Angelico wrote:



I do precisely that in many of my programs for e.g. single-line progress
displays.
But for multi-line output I don't know of any way to move the cursor
back up.
I work in Windows 10.

Try \x1b[A to move up a line, should work.

ChrisA

Got it working!  The answer is
 \x1b[1A
Thanks for the pointer!
Rob Cliffe
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[Python-ideas] Re: New feature

2020-10-16 Thread Joao S. O. Bueno

On Fri, 16 Oct 2020 at 08:00, Chris Angelico  wrote:

> On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
>  wrote:
> >
> >
> >
> > On 13/10/2020 23:35, Guido van Rossum wrote:
> > > Can one of the educators on the list explain why this is such a
> > > commonly required feature? I literally never feel the need to clear my
> > > screen -- but I've seen this requested quite a few times in various
> > > forms, often as a bug report "IDLE does not support CLS". I presume
> > > that this is a common thing in other programming environments for
> > > beginners -- even C++ (given that it was mentioned). Maybe it's a
> > > thing that command-line users on Windows are told to do frequently?
> > > What am I missing that students want to do frequently? Is it a
> > > holdover from the DOS age?
> > >
> > Sometimes I want a program that displays (more than 1 line of) real-time
> > information in a Windows CMD box and refreshes it every few seconds
> > (e.g. progress displays, monitoring open
> > files/locks/connections/downloads etc.).  It is natural to clear the
> > screen and display the updated information.
>
> Natural perhaps, but ugly. Much better to reposition the cursor and
> overwrite the previous text, with "clear to end of line" as required;
> that way, you avoid flicker.
>

Let me tell you what is ugly -
people doing `os.system("cls")` in otherwise what would otherwise
be a perfect multiplatform script.

And while we may question why people want this feature, fact is it is
requested
time and time again - and I'd find rather useful having it around when
answering
questions instead of having to say: "ok, if are on Mac or Linux, do
`print("\x1b[H")`, if you
are on windows `pip install colorama ...`.

Check for the occurrences of `os.system('cls')` in the Portuguese version
of stackoverflow, for example:
https://pt.stackoverflow.com/search?q=is%3Aanswer+os.system%28%27cls%27%29




> ChrisA
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[Python-ideas] Re: New feature

2020-10-16 Thread Chris Angelico

On Fri, Oct 16, 2020 at 11:08 PM Rob Cliffe  wrote:
>
>
>
> On 16/10/2020 11:59, Chris Angelico wrote:
> > On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
> >  wrote:
> >>
> >>
> >> On 13/10/2020 23:35, Guido van Rossum wrote:
> >>> Can one of the educators on the list explain why this is such a
> >>> commonly required feature? I literally never feel the need to clear my
> >>> screen -- but I've seen this requested quite a few times in various
> >>> forms, often as a bug report "IDLE does not support CLS". I presume
> >>> that this is a common thing in other programming environments for
> >>> beginners -- even C++ (given that it was mentioned). Maybe it's a
> >>> thing that command-line users on Windows are told to do frequently?
> >>> What am I missing that students want to do frequently? Is it a
> >>> holdover from the DOS age?
> >>>
> >> Sometimes I want a program that displays (more than 1 line of) real-time
> >> information in a Windows CMD box and refreshes it every few seconds
> >> (e.g. progress displays, monitoring open
> >> files/locks/connections/downloads etc.).  It is natural to clear the
> >> screen and display the updated information.
> > Natural perhaps, but ugly. Much better to reposition the cursor and
> > overwrite the previous text, with "clear to end of line" as required;
> > that way, you avoid flicker.
> >
> > C
> I do precisely that in many of my programs for e.g. single-line progress
> displays.
> But for multi-line output I don't know of any way to move the cursor
> back up.
> I work in Windows 10.

Try \x1b[A to move up a line, should work.

ChrisA
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[Python-ideas] Re: New feature

On 16/10/2020 11:59, Chris Angelico wrote:

On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
wrote:

On 13/10/2020 23:35, Guido van Rossum wrote:

Natural perhaps, but ugly. Much better to reposition the cursor and
overwrite the previous text, with "clear to end of line" as required;
that way, you avoid flicker.

C
I do precisely that in many of my programs for e.g. single-line progress
displays.
But for multi-line output I don't know of any way to move the cursor
back up.

I work in Windows 10.
Rob Cliffe
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[Python-ideas] Re: New feature

2020-10-16 Thread Chris Angelico

On Fri, Oct 16, 2020 at 8:21 PM Rob Cliffe via Python-ideas
 wrote:
>
>
>
> On 13/10/2020 23:35, Guido van Rossum wrote:
> > Can one of the educators on the list explain why this is such a
> > commonly required feature? I literally never feel the need to clear my
> > screen -- but I've seen this requested quite a few times in various
> > forms, often as a bug report "IDLE does not support CLS". I presume
> > that this is a common thing in other programming environments for
> > beginners -- even C++ (given that it was mentioned). Maybe it's a
> > thing that command-line users on Windows are told to do frequently?
> > What am I missing that students want to do frequently? Is it a
> > holdover from the DOS age?
> >
> Sometimes I want a program that displays (more than 1 line of) real-time
> information in a Windows CMD box and refreshes it every few seconds
> (e.g. progress displays, monitoring open
> files/locks/connections/downloads etc.).  It is natural to clear the
> screen and display the updated information.

Natural perhaps, but ugly. Much better to reposition the cursor and
overwrite the previous text, with "clear to end of line" as required;
that way, you avoid flicker.

ChrisA
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[Python-ideas] Re: New feature