[issue44325] IDLE: Fix shell comment anomalies

[Tal Einat]

Tal Einat  added the comment:

The sidebar doesn't seem to be causing this issue, it's just making it a bit 
more visible, since what was previously a blank line now also has a more 
visible "..." continuation prompt.

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[issue44325] IDLE: Fix shell comment anomalies

[Tal Einat]

Tal Einat  added the comment:

> However, I sometimes saw ... appear very briefly, only to be overwritten with 
> >>>.

This is a known limitation of the current sidebar implementation, which was 
very difficult to avoid and was considered minor enough to let be for now.

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[issue44325] IDLE: Fix shell comment anomalies

[Tal Einat]

Tal Einat  added the comment:

> 1) trailing whitespace (' ' and '\t' at least) is removed before this 
> function is called.  I presume in IDLE rather than code.II, but cannot find 
> where.  It is not with .rstrip.

You're probably looking for this code in 
EditorWindow.newline_and_indent_event():

# Strip whitespace after insert point.
while text.get("insert") in " \t":
text.delete("insert")

See: 
https://github.com/python/cpython/blob/89e50ab36fac6a0e7f1998501f36fcd2872a6604/Lib/idlelib/editor.py#L1390

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[issue44325] IDLE: Fix shell comment anomalies

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I added debug prints to _maybe_compile and confirmed

1) trailing whitespace (' ' and '\t' at least) is removed before this function 
is called.  I presume in IDLE rather than code.II, but cannot find where.  It 
is not with .rstrip.  (Note: doing so after '\' is a bug in that it lets buggy 
input such as 'a\ \n  + 2' run instead of raising.)

2. code is otherwise delivered intact and blanks lines become 'pass'.  Thus any 
difference noted above is not due to compile().

The report was based on Windows with 3.9.5, 3.10.0b2, and fresh main.  I 
repeated the Shell experiments on a Mac Airbook, and a slower machine, with 
3.10.b1.  There was never a spurious ... -- once the proper >>> was printed.  
However, I sometimes saw ... appear very briefly, only to be overwritten with 
>>>.  (I saw this once, *very briefly*, on Windows with main, on the first 
comment I tried.)  I also saw ... appear and disappear when there was a 
SyntaxError or print output.  I suspect that Sidebar always adds ..., only to 
be deleted or overwritten when it is a mistake.

I then tried 3.9.5 on the Mac and saw a spurious blank line with ' # a' once, 
on the first try, but not again in several attempts.  There seems to be a 
'warmup' effect.

My conclusion so far: sidebar might be a culprit, but because of the 3.9 
behavior, I think it more likely a victim of pyshell prematurely marking the 
new line as a possible continuation line.  As long as there was not 
continuation prompt, this might seem innocuous.  But it might also be a factor 
in other spurious blank lines.  In particular,

>>> if 1: # Hit return on indented line.
... print(2)
... 
... < undeleted 4 space indent
2
>>> if 1: # Delete indent first.  Get proper behavior.
... print(2)
...
2
>>>

I am stopping here.  Tal, what do you think with your better knowledge of 
pyshell internals?

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[issue44325] IDLE: Fix shell comment anomalies

[Terry J. Reedy]

New submission from Terry J. Reedy :

Spinoff from #38673, about standard REPL, msg356271 (me) and msg356348 (Guido). 
 In the following interactions, no blank lines were entered.

3.9 behavior
>>> #a
>>> # a
>>>  #a
>>>  # a
 
>>> 
Mystery 1: why the blank continuation line?

I previously wrote
"ast.dump(ast.parse(' # a\n', '', 'single')) gives the same result, 
'Module(body=[], type_ignores=[])', as without [space after #]".
Today, 3.8.10, 3.9.5, 3.10, and 3.11 say "unexpected EOF while parsing".

3.10 behavior
>>> #a
...  
>>> # a
>>>  #a
>>>  # a
...  
>>>
Mystery 2: why the new continuation line after '#a'?

3.11 behavior
>>> #a
>>> # a
>>> #a
>>>  #a
>>>  # a
...  
>>>
Mystery 3: why does the 3.10 regression for '#a' disappear?

Perhaps IDLE should handle initial blank lines itself, but I will investigate 
what codeop._maybe_compile is getting and doing in the different cases first.

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messages: 395214
nosy: taleinat, terry.reedy
priority: normal
severity: normal
stage: test needed
status: open
title: IDLE: Fix shell comment anomalies
type: behavior
versions: Python 3.10, Python 3.11, Python 3.9

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