[Python-ideas] Suggestion: Clear screen command for the REPL

[Terry Reedy]

On 9/17/2016 6:51 AM, João Matos wrote:
> Hello,
>
> I would like to suggest adding a clear command (not function) to Python.
> It's simple purpose would be to clear the REPL screen, leaving the >>>
> prompt at the top left of the screen.
>
> This is something very basic but also very useful for newbies learning
> Python from the REPL.
> After some trial and errors it is best to start with a clean screen.
> Clearing the screen helps clear your mind.
>
> Historically it is a common command in interpreted languages.

Python is not an 'interpreted' language in the sense that you are using 
the word.  It is a compiled language that includes its compile function 
as part of the runtime.  This enables an interactive mode.

Python does not have commands, only statements, expressions, and 
functions, etcetera.  This is why the 'exit()' and 'quit()' 'commands' 
are functions and require the parentheses.  In interactive mode, a 
statement consisting of a single indentifier (or expression) causes 
display of a representation of the resulting object.

You could request that the site module also add a clear() function. But 
the next problem is that clearing the screen is not a Python function 
and the Python runtime does not normally know how to do so.  The 
implementation of 'clear screen' is specific to the particular console 
or window or terminal emulation.  The control sequence for a window that 
emulates VT100 does not work on Windows Command Prompt (excepting 
possibly a non-default CP on Win 10) or necessarily IDLE or IPython or 
PyCharm or ... .  The only assumption that Python makes about the screen 
it is running on is that '\n' is interpreted as a newline.


IDLE has a 'Restart Shell' menu command with key binding.  It does not 
physically clear the screen but it draws a double line, which serves 
most of the 'clear the mind' purpose.  If there is an editor window 
open, one can close and reopen the Shell window to start really fresh.

At least on Windows, Select All (^A) + Del (or Backspace) is the common 
idiom for clearing an editor box in a GUI.  Is this used on other OSes? 
This works in an IDLE editor also.  It is disabled in the Shell because 
IDLE's original designers thought to protect beginners from doing such. 
A clear screen menu option has been requested, but it has never become a 
top priority.  In any case, this, like other current clear screen 
commands, would work because the command would go to the window manager 
and not to python.

-- 
Terry Jan Reedy