On Sat, Oct 17, 2020 at 05:44:12AM +1100, Chris Angelico wrote:
On Sat, Oct 17, 2020 at 5:40 AM Jonathan Crall <erotemic@gmail.com> 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