[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

I closed the issue because we decided to not document the function, but I'm 
still interested to mark the API is private. Such change is more sensitive, so 
I added it my larger "New C API" project which works on finding a way to 
deprecate functions and provide maybe helpers for backward and forward 
compatibility:
https://pythoncapi.readthedocs.io/bad_api.html#for-internal-use-only

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

Change by STINNER Victor :


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resolution: out of date -> wont fix

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

It seems like these functions should be documented, so I close the issue.

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resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[João Sebastião de Oliveira Bueno]

João Sebastião de Oliveira Bueno  added the comment:

This discussion is fresh, so maybe it is worth asking here prior to 
python-ideas:

In Python we can change any global variable, object attribute or mapping-value 
with function calls. Locals and nonlocals are the only exceptions and from time 
to time that gets in the way of clever oneliners, and it is just plain 
asymmetric. 

What do you say of adding a wrapper to this as an oficial Python function in 
the stdlib? Maybe inspect.setlocal() that could set f_locals and call this?? 
That would  provide a workaround to the asymmetry that locals currently 
experiment. 

It would not impose any extra security risks, since this can be called via 
ctypes already, and also it is not any more subject to abuse than setattr or 
globals()[...] =  can already be abused.

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nosy: +João.Sebastião.de.Oliveira.Bueno

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

> Currently you should call PyFrame_FastToLocalsWithError(), modify directly 
> f_locals, and call PyFrame_LocalsToFast().

When happens if PyFrame_LocalsToFast() isn't called? Does it crash or is it 
just slower?

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

frameobject.h is not included in any header file. Some effort was spent for 
avoiding including it in ceval.h, genobject.h, pystate.h and traceback.h. The 
whole content of frameobject.h is not available in the limited API. I'm not 
sure about the status of this API. This is not a very hight level API, but 
rather a very low level API. If document it, it should be documented on a 
separate page or on a page together with other low-level API.

> Serhiy: how are you supposed to modify local variables of a frame when these 
> variables are stored in "fast locals"?

Currently you should call PyFrame_FastToLocalsWithError(), modify directly 
f_locals, and call PyFrame_LocalsToFast(). This is very low-level manipulation. 
It exposes implementation details (at least you need to access PyFrameObject 
attributes directly). It should be documented that the most of PyFrame_* API is 
low-level and implementation specific. PyFrame_GetLineNumber() is an exception.

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

Serhiy: how are you supposed to modify local variables of a frame when these 
variables are stored in "fast locals"? Even if it's a rare useful, I think that 
it's ok to expose PyFrame_FastToLocalsWithError(), and maybe also 
PyFrame_FastToLocals().

It is useful you want write a debugger in pure C, and don't want to bother with 
fast locals special case.

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

> If I only convert PyFrame_New() then I would need to add it to as existing 
> page since the patch created a new page for Frame Objects.  I think the right 
> place would be under the current PyFrameObject in Doc/c-api/veryhigh.rst?

Not, it's a very high level API, it's a low level API which should be 
referenced in the concrete.rst page, as I didn in my patch.

I think it's ok to have a page with only two functions: PyFrame_New() and  
PyFrame_GetLineNumber().

Move https://docs.python.org/dev/c-api/reflection.html#c.PyFrame_GetLineNumber 
into your new doc, but leave something like "See also 
:c:func:`PyFrame_GetLineNumber`." there.

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[Cheryl Sabella]

Cheryl Sabella  added the comment:

Thanks Victor and Serhiy.

>> @Cheryl: Maybe convert the PR without PyFrame_FastToLocals() and 
>> PyFrame_FastToLocalsWithError().

If I only convert PyFrame_New() then I would need to add it to as existing page 
since the patch created a new page for Frame Objects.  I think the right place 
would be under the current PyFrameObject in Doc/c-api/veryhigh.rst?

Thanks!

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

Ah, PyFrame_GetLineNumber is now documented at Doc/c-api/reflection.rst. But 
PyFrame_New() is still not documented. So my patch is not completely useful.

@Cheryl: Maybe convert the PR without PyFrame_FastToLocals() and 
PyFrame_FastToLocalsWithError().

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

> PyFrame_FastToLocals() and PyFrame_LocalsToFast() are not documented and have 
> weird interface. I think the use of them should be discouraged.

I suggest to document them, but explain in the documentation that they must not 
be used :-)

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor  added the comment:

> Should there be a PR for this?

Feel free to create a PR from my old (4 years old) patch. Just mention my name 
in the commit message please.

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

PyFrameObject already is documented in Doc/c-api/veryhigh.rst.
PyFrame_GetLineNumber() already is documented in Doc/c-api/reflection.rst.

PyFrame_FastToLocals() and PyFrame_LocalsToFast() are not documented and have 
weird interface. I think the use of them should be discouraged.

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nosy: +serhiy.storchaka

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[Cheryl Sabella]

Cheryl Sabella added the comment:

Victor,

Should there be a PR for this?

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nosy: +csabella

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

STINNER Victor added the comment:

c_api_frame.patch: document some C functions of the frame object in the C API.

--
keywords: +patch
Added file: http://bugs.python.org/file32537/c_api_frame.patch

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[issue19431] Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()

[STINNER Victor]

New submission from STINNER Victor:

(Copy of an email) Georg Brandl via python.org 

Am 29.10.2013 01:19, schrieb victor.stinner:
 http://hg.python.org/cpython/rev/4ef4578db38a
 changeset:   86715:4ef4578db38a
 user:Victor Stinner victor.stin...@gmail.com
 date:Tue Oct 29 01:19:37 2013 +0100
 summary:
   Issue #18408: Add a new PyFrame_FastToLocalsWithError() function to handle
 exceptions when merging fast locals into f_locals of a frame.
 PyEval_GetLocals() now raises an exception and return NULL on failure.

You'll have to either make this private or document it.

--
assignee: docs@python
components: Documentation
messages: 201618
nosy: docs@python, georg.brandl, haypo, pitrou
priority: normal
severity: normal
status: open
title: Document PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()
versions: Python 3.3, Python 3.4

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