bug#20897: 25.0.50; [python] sexp-movement are confusing

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Rasmus]

Hi,

Sexp movement in python.el are very confusing to me.  I know that logical
sexp movements outside lisp are subjective, and I know that the behavior
isn't wrong.  I understand why it does what it does.  The behavior is just
confusing when I use it an practice.

Example, starting from emacs -q:

Open test.py

Insert something like this, ignoring point denoted by "{v,^} {1,...,5}".

4  5   6
v  v   v
def foo(x):
   """return x as one"""

    x = 1;

    return(x)
   ^      ^  ^
   2      3  1

Consider points 1,...,5.  At point 2 forward-sexp will go to point 1, at
point 3 backward-sexp will go to point 2.  At point 1, sexp-backward will
go to 4 rather than point 2 (as I would expect).  Likewise, at point 4,
forward sexp goes to point 1 rather than 5.  At point five, everything is
as I would expect, and {forward,backward}-sexp goes to 6 and 4.

A switch to prefer a closer opening/closing of the "sexp" at point would
be great.

Thanks,
Rasmus

In GNU Emacs 25.0.50.2 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.4)
 of 2015-06-21 on x200s
Repository revision: 821a3633564f36857968c7fe2b8bb6681a895905
Windowing system distributor `The X.Org Foundation', version 11.0.11702000
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Configured features:
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Important settings:
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-- 
Dung makes an excellent fertilizer

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Andreas Röhler]

Am 25.06.2015 um 17:53 schrieb Rasmus:
> Hi,
>
> Sexp movement in python.el are very confusing to me.  I know that logical
> sexp movements outside lisp are subjective,

Not more as anything else editor-related. Languages are composed by 
elements, which a syntax may describe. Even if an editor must not be the 
slave of a syntax, it should be aware of.


>   and I know that the behavior
> isn't wrong.

It behaves arbitrary WRT Python syntax, that's wrong.

>   I understand why it does what it does.  The behavior is just
> confusing when I use it an practice.
>
> Example, starting from emacs -q:
>
> Open test.py
>
> Insert something like this, ignoring point denoted by "{v,^} {1,...,5}".
>
> 4  5   6
> v  v   v
> def foo(x):
>     """return x as one"""
>
>      x = 1;
>
>      return(x)
>     ^      ^  ^
>     2      3  1
>
> Consider points 1,...,5.  At point 2 forward-sexp will go to point 1, at
> point 3 backward-sexp will go to point 2.  At point 1, sexp-backward will
> go to 4 rather than point 2 (as I would expect).  Likewise, at point 4,
> forward sexp goes to point 1 rather than 5.  At point five, everything is
> as I would expect, and {forward,backward}-sexp goes to 6 and 4.
>
> A switch to prefer a closer opening/closing of the "sexp" at point would
> be great.
>
> Thanks,
> Rasmus
>

[ ... ]

Python is composed by expressions.
If inside an expression C-M-f should to to its end.

 From end to next end same level if existing - or level up, or next 
top-level-form, or nil at EOB

Backward and forward needs to be consistent.

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Rasmus]

Hi,

Andreas Röhler <andreas.roehler@easy-emacs.de> writes:

>> Sexp movement in python.el are very confusing to me.  I know that logical
>> sexp movements outside lisp are subjective,
>
> Not more as anything else editor-related. Languages are composed by
> elements, which a syntax may describe. Even if an editor must not be
> the slave of a syntax, it should be aware of.

That is probably true.  I really just want to be able to bent python.el to
work with my internal "fast" logic which controls how I type on keyboard.

>>   and I know that the behavior
>> isn't wrong.
>
> It behaves arbitrary WRT Python syntax, that's wrong.

OK.  I'm not sure.  I can somehow imagine parentheses that would justify
the movements cf. below.  But in lisp it would not go from one "nesting"
to another, which is essentially what bugs me.


> Python is composed by expressions.
> If inside an expression C-M-f should to to its end.
>
> From end to next end same level if existing - or level up, or next
> top-level-form, or nil at EOB
>
> Backward and forward needs to be consistent.

I'm not sure I understand.

The way I think about it is like the following.  If I'm at point 2 and
move backward I really want to be a point 1.  But in python point 0 and 1
is the same, so it assumes the outer level which has end point 4.  But I
at most want to go to point 3, closing the "nearest" "sexp".

01     2          3
vv     v          V
((defun name (arg))
 ...)
     ^ 
     4

Rasmus

-- 
Don't panic!!!

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Andreas Röhler]

Am 25.06.2015 um 18:46 schrieb Rasmus:
> Hi,
>
> Andreas Röhler <andreas.roehler@easy-emacs.de> writes:
>
>>> Sexp movement in python.el are very confusing to me.  I know that logical
>>> sexp movements outside lisp are subjective,
>> Not more as anything else editor-related. Languages are composed by
>> elements, which a syntax may describe. Even if an editor must not be
>> the slave of a syntax, it should be aware of.
> That is probably true.  I really just want to be able to bent python.el to
> work with my internal "fast" logic which controls how I type on keyboard.
>
>>>    and I know that the behavior
>>> isn't wrong.
>> It behaves arbitrary WRT Python syntax, that's wrong.
> OK.  I'm not sure.  I can somehow imagine parentheses that would justify
> the movements cf. below.  But in lisp it would not go from one "nesting"
> to another, which is essentially what bugs me.
>
>
>> Python is composed by expressions.
>> If inside an expression C-M-f should to to its end.
>>
>>  From end to next end same level if existing - or level up, or next
>> top-level-form, or nil at EOB
>>
>> Backward and forward needs to be consistent.
> I'm not sure I understand.
>
> The way I think about it is like the following.  If I'm at point 2 and
> move backward I really want to be a point 1.

Don't think so WRT picture below. From end of symbol "defun" it move 
back to beginning "d".
Because "defun" is an element of the list.
Next C-M-b should go up backward - but fails. A design flaw IMO.

>   But in python point 0 and 1
> is the same, so it assumes the outer level which has end point 4.  But I
> at most want to go to point 3, closing the "nearest" "sexp".
>
> 01     2          3
> vv     v          V
> ((defun name (arg))
>   ...)
>       ^
>       4
>
> Rasmus
>
Not sure if I understand the double paren at picture. Rules are simple 
anyway: Either there is an element of same level, reach that. Or go up. 
Or go the end.

You could try py-forward-expression, py-backward-expression.
Just to study the behavior.

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Stefan Monnier]

> If inside an expression C-M-f should to to its end.

No, as explained elsewhere, C-M-f's binding is a binding that goes to
the end of the expression that immediately *follows* point.  If we're
*inside* a sexp, the way to jump to its end is up-list.

I understand you want/like to jump to the end of the enclosing
expression, and that's fine, but this is not what C-M-f should do
by default.


        Stefan

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Daniel Colascione]

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On 06/25/2015 09:48 PM, Stefan Monnier wrote:
>> If inside an expression C-M-f should to to its end.
> 
> No, as explained elsewhere, C-M-f's binding is a binding that goes to
> the end of the expression that immediately *follows* point.  If we're
> *inside* a sexp, the way to jump to its end is up-list.
> 
> I understand you want/like to jump to the end of the enclosing
> expression, and that's fine, but this is not what C-M-f should do
> by default.

"Right" or "wrong" aside, Python's current default behavior is just
inconsistent with other modes for infix-expression languages. I tried
for a long time to use the default behavior --- maybe there was some
efficiency advantage that would take time to appear --- but I ended up
just giving up and making python-mode work like other modes.


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bug#20897: 25.0.50; [python] sexp-movement are confusing

[Stefan Monnier]

> "Right" or "wrong" aside, Python's current default behavior is just
> inconsistent with other modes

My comment was only about the part of Andreas's text which I quoted.
It is actually unrelated to this bug-report.  Sorry 'bout that,


        Stefan

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Andreas Röhler]

Am 26.06.2015 um 04:03 schrieb Daniel Colascione:
> On 06/25/2015 09:48 PM, Stefan Monnier wrote:
>>> If inside an expression C-M-f should to to its end.
>> No, as explained elsewhere, C-M-f's binding is a binding that goes to
>> the end of the expression that immediately *follows* point.  If we're
>> *inside* a sexp, the way to jump to its end is up-list.
>>
>> I understand you want/like to jump to the end of the enclosing
>> expression, and that's fine, but this is not what C-M-f should do
>> by default.
> "Right" or "wrong" aside, Python's current default behavior is just
> inconsistent with other modes for infix-expression languages. I tried
> for a long time to use the default behavior --- maybe there was some
> efficiency advantage that would take time to appear --- but I ended up
> just giving up and making python-mode work like other modes.
>

If you could try python-mode.el's py-forward/backward-expression 
commands, that would be much appreciated. Won't be surprised, should 
some bug show-up there too - just don't see any at the moment.

Thanks all,

Andreas

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Andreas Röhler]

Am 26.06.2015 um 04:03 schrieb Daniel Colascione:
> On 06/25/2015 09:48 PM, Stefan Monnier wrote:
>>> If inside an expression C-M-f should to to its end.
>> No, as explained elsewhere, C-M-f's binding is a binding that goes to
>> the end of the expression that immediately *follows* point.  If we're
>> *inside* a sexp, the way to jump to its end is up-list.
>>
>> I understand you want/like to jump to the end of the enclosing
>> expression, and that's fine, but this is not what C-M-f should do
>> by default.
> "Right" or "wrong" aside, Python's current default behavior is just
> inconsistent with other modes for infix-expression languages. I tried
> for a long time to use the default behavior --- maybe there was some
> efficiency advantage that would take time to appear --- but I ended up
> just giving up and making python-mode work like other modes.
>

Just to give an example syntax-oriented doesn't mean being enslaved by 
syntax: operators in Python are expressions, but sexp should jump over, 
as symbol-at-point is available.  In case some more specific is needed, 
py-partial-expression is delivered.

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Lars Ingebrigtsen]

Rasmus <rasmus@gmx.us> writes:

> Open test.py
>
> Insert something like this, ignoring point denoted by "{v,^} {1,...,5}".
>
> 4  5   6
> v  v   v
> def foo(x):
>    """return x as one"""
>
>     x = 1;
>
>     return(x)
>    ^      ^  ^
>    2      3  1
>
> Consider points 1,...,5.  At point 2 forward-sexp will go to point 1, at
> point 3 backward-sexp will go to point 2.  At point 1, sexp-backward will
> go to 4 rather than point 2 (as I would expect).  Likewise, at point 4,
> forward sexp goes to point 1 rather than 5.  At point five, everything is
> as I would expect, and {forward,backward}-sexp goes to 6 and 4.

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

Point movement at 2 has been fixed -- it now goes to 3 (in Emacs 29),
not 1.

As for the other points here -- that C-M-<right> at 4 shouldn't move to
1 -- I think that would be pretty surprising.  That is, these commands
(try to) move by semantic unit, which is ambiguous in languages like
Python, so people have differing opinions.  But as far as I can tell,
python-mode here works as designed, so I'm therefore closing this bug
report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#20897: 25.0.50; [python] sexp-movement are confusing

[Kévin Le Gouguec]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> As for the other points here -- that C-M-<right> at 4 shouldn't move to
> 1 -- I think that would be pretty surprising.  That is, these commands
> (try to) move by semantic unit, which is ambiguous in languages like
> Python, so people have differing opinions.  But as far as I can tell,
> python-mode here works as designed, so I'm therefore closing this bug
> report.

FWIW, 28.1 introduces python-forward-sexp-function, which can be set to
nil to have something that is, quoting the Custom tag, more "CC-mode
like".

For older versions, the commentary of python.el suggests an equivalent
way to tweak sexp movement.

I haven't checked if this option satisfies all of the OP's expectations;
still, I figured it was worth mentioning in this thread FTR.