[Python-Dev] PEP 580 (C call protocol) minor update

[Jeroen Demeyer]

I made some minor updates to PEP 580 (PEP editors: please merge 
https://github.com/python/peps/pull/741) and its reference implementation:


- Added a new introductory section explaining the basic idea.

- The C protocol no longer deals with __name__; a __name__ attribute is 
required but the protocol does not deal with its implementation.


- The PEP no longer deals with profiling. This means that profiling only 
works for actual instances of builtin_function_or_method and 
method_descriptor. Profiling arbitrary callables would be nice, but that 
is deferred to a future PEP.


The last two items are meant to simplify the PEP (although this is 
debatable since "simple" is very subjective).



Enjoy!
Jeroen.
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[Python-Dev] Question about PEP 484

[Adam Cataldo via Python-Dev]

*Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
manager for the Python team at Google. Rebecca Chen, our lead pytype
 contributor, and I are interested in
helping finalize PEP 484 if possible. To that end, we wanted to find out
what technical issues the PEP 484 authors feel they still need to finalize.
We also wanted to know how we can help.We have a large Python code base at
Google, and may be able to use this to help resolve current incomplete
definitions, by collecting data on how types are used. We also have a
couple ambiguities that we’d love to get closure on: - One thing we care
about in particular, given the implementation of pytype, is the detailed
definition of what goes in a .pyi file. Do folks think this makes sense to
include as part of PEP 484, or would this be better in a separate PEP? We’d
love to get your thoughts.- The relationship between unicode and
typing.Text in Python 2 has been a recurring source of confusion for our
users. Especially since we contributed
 to the current state of affairs,
we’d like to figure out how to establish clarity here.Thoughts?Thanks,Adam*
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Re: [Python-Dev] Question about PEP 484

[Brett Cannon]

On Mon, 16 Jul 2018 at 10:32 Adam Cataldo via Python-Dev <
python-dev@python.org> wrote:

>
>
>
>
>
> *Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
> manager for the Python team at Google. Rebecca Chen, our lead pytype
>  contributor, and I are interested in
> helping finalize PEP 484 if possible. To that end, we wanted to find out
> what technical issues the PEP 484 authors feel they still need to finalize.
> We also wanted to know how we can help.We have a large Python code base at
> Google, and may be able to use this to help resolve current incomplete
> definitions, by collecting data on how types are used. We also have a
> couple ambiguities that we’d love to get closure on: - One thing we care
> about in particular, given the implementation of pytype, is the detailed
> definition of what goes in a .pyi file. Do folks think this makes sense to
> include as part of PEP 484, or would this be better in a separate PEP? We’d
> love to get your thoughts.*
>

What specifically do you want beyond
https://www.python.org/dev/peps/pep-0484/#stub-files?


>
>
>
> * - The relationship between unicode and typing.Text in Python 2 has been
> a recurring source of confusion for our users. Especially since we
> contributed  to the current state
> of affairs, we’d like to figure out how to establish clarity here.Thoughts?*
>

Do be aware, Adam, that due to Guido's retirement last week people might be
a bit preoccupied and so a little slow in responding. But then again Guido
just got a bit more free time so he might chime in on this one. ;)
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Re: [Python-Dev] Question about PEP 484

[Teddy Sudol via Python-Dev]

Hi, my name is Teddy Sudol. I work with Adam and Rebecca on pytype.

The explanation of stub files is unclear. The section you linked starts
with, "Stub files are files containing type hints that are only for use by
the type checker, not at runtime." According to
https://www.python.org/dev/peps/pep-0484/#acceptable-type-hints, type hints
may be classes, abstract base classes, types defined in the `types` and
`typing` modules, type variables, type aliases and None. Further in the
section you linked, PEP 484 also states, "Stub files have the same syntax
as regular Python modules," and, "no runtime behavior should be expected of
stub files."

"Have the same syntax as regular Python modules" and "are files containing
type hints" are at odds with each other. This has led to compatibility
issues between Mypy and pytype. For example, `b''` is not a valid type
annotation, but until a month ago, `codecs.pyi` in typeshed used exactly
that:
https://github.com/python/typeshed/commit/6bbf3d89eb9b6c3fd5b0c0f632b2ad9258cecf15#diff-5f6f48c425bc0c283784cf5277880c0cL95.
If statements can be useful for things like version checks, but on the
other hand, pyi files aren't supposed to have any runtime behavior.
Additionally, codifying the syntax for pyi files would settle questions
like whether constants should be typed using "x: " or "x = ...
# type: ".

We would like to see a clear statement about the syntax of stub files.
Personally, I think they should be a subset of Python, but I'd also be
happy with an EBNF grammar for them.

-- Teddy


On Mon, Jul 16, 2018 at 11:05 AM Brett Cannon  wrote:

>
>
> On Mon, 16 Jul 2018 at 10:32 Adam Cataldo via Python-Dev <
> python-dev@python.org> wrote:
>
>>
>>
>>
>>
>>
>> *Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
>> manager for the Python team at Google. Rebecca Chen, our lead pytype
>>  contributor, and I are interested in
>> helping finalize PEP 484 if possible. To that end, we wanted to find out
>> what technical issues the PEP 484 authors feel they still need to finalize.
>> We also wanted to know how we can help.We have a large Python code base at
>> Google, and may be able to use this to help resolve current incomplete
>> definitions, by collecting data on how types are used. We also have a
>> couple ambiguities that we’d love to get closure on: - One thing we care
>> about in particular, given the implementation of pytype, is the detailed
>> definition of what goes in a .pyi file. Do folks think this makes sense to
>> include as part of PEP 484, or would this be better in a separate PEP? We’d
>> love to get your thoughts.*
>>
>
> What specifically do you want beyond
> https://www.python.org/dev/peps/pep-0484/#stub-files?
>
>
>>
>>
>>
>> * - The relationship between unicode and typing.Text in Python 2 has been
>> a recurring source of confusion for our users. Especially since we
>> contributed  to the current state
>> of affairs, we’d like to figure out how to establish clarity here.Thoughts?*
>>
>
> Do be aware, Adam, that due to Guido's retirement last week people might
> be a bit preoccupied and so a little slow in responding. But then again
> Guido just got a bit more free time so he might chime in on this one. ;)
>
> --
> You received this message because you are subscribed to the Google Groups
> "pytype" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to pytype+unsubscr...@googlegroups.com.
> To post to this group, send email to pyt...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/pytype/CAP1%3D2W4NxcsSdsiMrh55KhjkwgD0PGRcZJF_Azq3g6QFQ2oiAw%40mail.gmail.com
> 
> .
> For more options, visit https://groups.google.com/d/optout.
>
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Re: [Python-Dev] Question about PEP 484

[Adam Cataldo via Python-Dev]

Thanks Brett and Teddy,

Just so it doesn't get lost in the shuffle as folks dive into details, I'll
re-ask my earlier question about stub files. Assuming there is consensus
that there is ambiguity to resolve in the current definition, is updating
the section on stub files the preferred option? The only alternative I can
think of is to pull this out into a separate PEP. I frankly have no opinion
on what the best way to capture this is. We're happy to help out either way.

On Mon, Jul 16, 2018 at 12:48 PM Teddy Sudol  wrote:

> Hi, my name is Teddy Sudol. I work with Adam and Rebecca on pytype.
>
> The explanation of stub files is unclear. The section you linked starts
> with, "Stub files are files containing type hints that are only for use by
> the type checker, not at runtime." According to
> https://www.python.org/dev/peps/pep-0484/#acceptable-type-hints, type
> hints may be classes, abstract base classes, types defined in the `types`
> and `typing` modules, type variables, type aliases and None. Further in the
> section you linked, PEP 484 also states, "Stub files have the same syntax
> as regular Python modules," and, "no runtime behavior should be expected of
> stub files."
>
> "Have the same syntax as regular Python modules" and "are files containing
> type hints" are at odds with each other. This has led to compatibility
> issues between Mypy and pytype. For example, `b''` is not a valid type
> annotation, but until a month ago, `codecs.pyi` in typeshed used exactly
> that:
> https://github.com/python/typeshed/commit/6bbf3d89eb9b6c3fd5b0c0f632b2ad9258cecf15#diff-5f6f48c425bc0c283784cf5277880c0cL95.
> If statements can be useful for things like version checks, but on the
> other hand, pyi files aren't supposed to have any runtime behavior.
> Additionally, codifying the syntax for pyi files would settle questions
> like whether constants should be typed using "x: " or "x = ...
> # type: ".
>
> We would like to see a clear statement about the syntax of stub files.
> Personally, I think they should be a subset of Python, but I'd also be
> happy with an EBNF grammar for them.
>
> -- Teddy
>
>
> On Mon, Jul 16, 2018 at 11:05 AM Brett Cannon  wrote:
>
>>
>>
>> On Mon, 16 Jul 2018 at 10:32 Adam Cataldo via Python-Dev <
>> python-dev@python.org> wrote:
>>
>>>
>>>
>>>
>>>
>>>
>>> *Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
>>> manager for the Python team at Google. Rebecca Chen, our lead pytype
>>>  contributor, and I are interested in
>>> helping finalize PEP 484 if possible. To that end, we wanted to find out
>>> what technical issues the PEP 484 authors feel they still need to finalize.
>>> We also wanted to know how we can help.We have a large Python code base at
>>> Google, and may be able to use this to help resolve current incomplete
>>> definitions, by collecting data on how types are used. We also have a
>>> couple ambiguities that we’d love to get closure on: - One thing we care
>>> about in particular, given the implementation of pytype, is the detailed
>>> definition of what goes in a .pyi file. Do folks think this makes sense to
>>> include as part of PEP 484, or would this be better in a separate PEP? We’d
>>> love to get your thoughts.*
>>>
>>
>> What specifically do you want beyond
>> https://www.python.org/dev/peps/pep-0484/#stub-files?
>>
>>
>>>
>>>
>>>
>>> * - The relationship between unicode and typing.Text in Python 2 has
>>> been a recurring source of confusion for our users. Especially since we
>>> contributed  to the current state
>>> of affairs, we’d like to figure out how to establish clarity here.Thoughts?*
>>>
>>
>> Do be aware, Adam, that due to Guido's retirement last week people might
>> be a bit preoccupied and so a little slow in responding. But then again
>> Guido just got a bit more free time so he might chime in on this one. ;)
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "pytype" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to pytype+unsubscr...@googlegroups.com.
>> To post to this group, send email to pyt...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/pytype/CAP1%3D2W4NxcsSdsiMrh55KhjkwgD0PGRcZJF_Azq3g6QFQ2oiAw%40mail.gmail.com
>> 
>> .
>> For more options, visit https://groups.google.com/d/optout.
>>
>
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[Python-Dev] Specification of C function profiling?

[Jeroen Demeyer]

Hello,

it seems to me that there is no clear specification for the 
sys.setprofile() event c_call: the docs say "A C function is about to be 
called" but it's not clear what that means exactly, in particular when 
that C function is an unbound method like list.append.


I also noticed that Lib/test/test_sys_setprofile.py doesn't test any of 
the c_* events.


I'm asking in the context of https://bugs.python.org/issue34125
I found out that list.append([], None) *does* generate a c_call event 
but list.append([], None, **{}) does not.



Jeroen.
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Re: [Python-Dev] Question about PEP 484

[Guido van Rossum]

As one of the authors of PEP 484, *I* never thought there was an ambiguity
here. The intention was for stub files to conform to the same grammar as
regular .py files, but with a different interpretation.

> "Have the same syntax as regular Python modules" and "are files
containing type hints" are at odds with each other.

That depends. *same syntax as regular Python* is normative while
*containing type hints* is an informal description of intent.

I happen to be somewhat familiar with the situation that lead to this
question -- pytype has its own parser for stub files that cannot parse all
Python constructs. But claiming that PEP 484 is ambiguous feels wrong, and
if we really need to clarify it the only way to go is to make "same syntax
as regular Python" more clearly normative. Type checkers should of course
feel free ignore everything they don't care about.

Regarding the unicode issue, that is indeed unfortunate, and there's a long
but inconclusive discussion at https://github.com/python/typing/issues/208.
(If you want a longer discussion here please start a new subject.)

On Mon, Jul 16, 2018 at 1:02 PM, Adam Cataldo via Python-Dev <
python-dev@python.org> wrote:

> Thanks Brett and Teddy,
>
> Just so it doesn't get lost in the shuffle as folks dive into details,
> I'll re-ask my earlier question about stub files. Assuming there is
> consensus that there is ambiguity to resolve in the current definition, is
> updating the section on stub files the preferred option? The only
> alternative I can think of is to pull this out into a separate PEP. I
> frankly have no opinion on what the best way to capture this is. We're
> happy to help out either way.
>
> On Mon, Jul 16, 2018 at 12:48 PM Teddy Sudol  wrote:
>
>> Hi, my name is Teddy Sudol. I work with Adam and Rebecca on pytype.
>>
>> The explanation of stub files is unclear. The section you linked starts
>> with, "Stub files are files containing type hints that are only for use by
>> the type checker, not at runtime." According to
>> https://www.python.org/dev/peps/pep-0484/#acceptable-type-hints, type
>> hints may be classes, abstract base classes, types defined in the `types`
>> and `typing` modules, type variables, type aliases and None. Further in the
>> section you linked, PEP 484 also states, "Stub files have the same syntax
>> as regular Python modules," and, "no runtime behavior should be expected of
>> stub files."
>>
>> "Have the same syntax as regular Python modules" and "are files
>> containing type hints" are at odds with each other. This has led to
>> compatibility issues between Mypy and pytype. For example, `b''` is not a
>> valid type annotation, but until a month ago, `codecs.pyi` in typeshed used
>> exactly that: https://github.com/python/typeshed/commit/
>> 6bbf3d89eb9b6c3fd5b0c0f632b2ad9258cecf15#diff-
>> 5f6f48c425bc0c283784cf5277880c0cL95. If statements can be useful for
>> things like version checks, but on the other hand, pyi files aren't
>> supposed to have any runtime behavior. Additionally, codifying the syntax
>> for pyi files would settle questions like whether constants should be typed
>> using "x: " or "x = ...  # type: ".
>>
>> We would like to see a clear statement about the syntax of stub files.
>> Personally, I think they should be a subset of Python, but I'd also be
>> happy with an EBNF grammar for them.
>>
>> -- Teddy
>>
>>
>> On Mon, Jul 16, 2018 at 11:05 AM Brett Cannon  wrote:
>>
>>>
>>>
>>> On Mon, 16 Jul 2018 at 10:32 Adam Cataldo via Python-Dev <
>>> python-dev@python.org> wrote:
>>>





 *Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
 manager for the Python team at Google. Rebecca Chen, our lead pytype
  contributor, and I are interested in
 helping finalize PEP 484 if possible. To that end, we wanted to find out
 what technical issues the PEP 484 authors feel they still need to finalize.
 We also wanted to know how we can help.We have a large Python code base at
 Google, and may be able to use this to help resolve current incomplete
 definitions, by collecting data on how types are used. We also have a
 couple ambiguities that we’d love to get closure on: - One thing we care
 about in particular, given the implementation of pytype, is the detailed
 definition of what goes in a .pyi file. Do folks think this makes sense to
 include as part of PEP 484, or would this be better in a separate PEP? We’d
 love to get your thoughts.*

>>>
>>> What specifically do you want beyond https://www.python.org/dev/
>>> peps/pep-0484/#stub-files?
>>>
>>>



 * - The relationship between unicode and typing.Text in Python 2 has
 been a recurring source of confusion for our users. Especially since we
 contributed  to the current state
 of affairs, we’d like to figure out how to establish clarity 
 here.Thoughts?*

>>>
>>>

Re: [Python-Dev] Question about PEP 484

[Jelle Zijlstra]

2018-07-16 10:21 GMT-07:00 Adam Cataldo via Python-Dev <
python-dev@python.org>:

>
>
>
>
>
> *Hi Folks,Cc: Rebecca, pytypeThis is Adam Cataldo; I’m the engineering
> manager for the Python team at Google. Rebecca Chen, our lead pytype
>  contributor, and I are interested in
> helping finalize PEP 484 if possible. To that end, we wanted to find out
> what technical issues the PEP 484 authors feel they still need to finalize.
> We also wanted to know how we can help.We have a large Python code base at
> Google, and may be able to use this to help resolve current incomplete
> definitions, by collecting data on how types are used. We also have a
> couple ambiguities that we’d love to get closure on: - One thing we care
> about in particular, given the implementation of pytype, is the detailed
> definition of what goes in a .pyi file. Do folks think this makes sense to
> include as part of PEP 484, or would this be better in a separate PEP? We’d
> love to get your thoughts.*
>

I would be happy to contribute to this if that would be useful for type
checkers like pytype, although like Guido I don't think the current text of
the PEP is ambiguous. Typeshed already has a set of lint rules that limit
what can be put in stub files, but it could be useful to communicate the
exact set of allowed constructs.


>
> * - The relationship between unicode and typing.Text in Python 2 has been
> a recurring source of confusion for our users. Especially since we
> contributed  to the current state
> of affairs, we’d like to figure out how to establish clarity here.*
>
There has already been a long discussion on the typing issue tracker that
resulted in no consensus for any change to the current recommendation.
Perhaps there is something we can do, but it's not clear to me what that
would be.

>
>
> *Thoughts?Thanks,Adam*
>
>
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Re: [Python-Dev] Question about PEP 484

[Gregory P. Smith]

On Mon, Jul 16, 2018 at 1:44 PM Guido van Rossum  wrote:

> As one of the authors of PEP 484, *I* never thought there was an ambiguity
> here. The intention was for stub files to conform to the same grammar as
> regular .py files, but with a different interpretation.
>
> > "Have the same syntax as regular Python modules" and "are files
> containing type hints" are at odds with each other.
>
> That depends. *same syntax as regular Python* is normative while
> *containing type hints* is an informal description of intent.
>
> I happen to be somewhat familiar with the situation that lead to this
> question -- pytype has its own parser for stub files that cannot parse all
> Python constructs. But claiming that PEP 484 is ambiguous feels wrong, and
> if we really need to clarify it the only way to go is to make "same syntax
> as regular Python" more clearly normative. Type checkers should of course
> feel free ignore everything they don't care about.
>

I feel like the "same syntax as regular Python" is too broad a statement.
That effectively requires a version specific Python interpreter to execute
the files.  With at least four different Python static analyzers in
existence today, keeping the behavior of all of them consistent is
important.  Otherwise pyi files will be (are being) created that are
analyzer specific and break other type checkers when distributed.

ex: We're encountering pyi files with conditional logic in them.  I believe
we've encountered pyi files with del statements in them?  Both of these are
a slippery slope towards being turing complete in something that isn't
supposed to be code.  I don't like this.  Interface declarations should not
contain logic.  If we allow conditions, we need to explicitly define what
we do allow in the PEP.  (if+else and del?  what inputs are allowed for the
expression in if statements?).  Otherwise at some point someone is going to
create a pyi file containing loops, function calls, and generator
expressions and expect it to _do_ something.  The horror!  Lets avoid that.

PEP-484 does contain the text, "This also reinforces the notion that no
runtime behavior should be expected of stub files." But reinforcing a
notion is not what I read as a concrete statement.

I'd rather see that say something like, "There must not be any runtime
behavior from a stub file. They will be parsed for information, not
executed."  Wordsmith that all you want, I'm not pedantic enough. :)
I expect someone pedantic to happily point out that a def or class or
assignment to ... with an annotation is runtime behavior... technically
correct, but that isn't how people like me think of them in this context.

We use a Pythonic syntax for stubs to be consistent with the language, that
doesn't mean they are code.

I wrote more than I thought I would here, I'll stop now. :)

-gps


>
> Regarding the unicode issue, that is indeed unfortunate, and there's a
> long but inconclusive discussion at
> https://github.com/python/typing/issues/208. (If you want a longer
> discussion here please start a new subject.)
>
> On Mon, Jul 16, 2018 at 1:02 PM, Adam Cataldo via Python-Dev <
> python-dev@python.org> wrote:
>
>> Thanks Brett and Teddy,
>>
>> Just so it doesn't get lost in the shuffle as folks dive into details,
>> I'll re-ask my earlier question about stub files. Assuming there is
>> consensus that there is ambiguity to resolve in the current definition, is
>> updating the section on stub files the preferred option? The only
>> alternative I can think of is to pull this out into a separate PEP. I
>> frankly have no opinion on what the best way to capture this is. We're
>> happy to help out either way.
>>
>> On Mon, Jul 16, 2018 at 12:48 PM Teddy Sudol  wrote:
>>
>>> Hi, my name is Teddy Sudol. I work with Adam and Rebecca on pytype.
>>>
>>> The explanation of stub files is unclear. The section you linked starts
>>> with, "Stub files are files containing type hints that are only for use by
>>> the type checker, not at runtime." According to
>>> https://www.python.org/dev/peps/pep-0484/#acceptable-type-hints, type
>>> hints may be classes, abstract base classes, types defined in the `types`
>>> and `typing` modules, type variables, type aliases and None. Further in the
>>> section you linked, PEP 484 also states, "Stub files have the same syntax
>>> as regular Python modules," and, "no runtime behavior should be expected of
>>> stub files."
>>>
>>> "Have the same syntax as regular Python modules" and "are files
>>> containing type hints" are at odds with each other. This has led to
>>> compatibility issues between Mypy and pytype. For example, `b''` is not a
>>> valid type annotation, but until a month ago, `codecs.pyi` in typeshed used
>>> exactly that:
>>> https://github.com/python/typeshed/commit/6bbf3d89eb9b6c3fd5b0c0f632b2ad9258cecf15#diff-5f6f48c425bc0c283784cf5277880c0cL95.
>>> If statements can be useful for things like version checks, but on the
>>> other hand, pyi files aren't supposed to have

Re: [Python-Dev] Question about PEP 484

[Guido van Rossum]

On Mon, Jul 16, 2018 at 2:56 PM, Gregory P. Smith  wrote:

>
> On Mon, Jul 16, 2018 at 1:44 PM Guido van Rossum  wrote:
>
>> As one of the authors of PEP 484, *I* never thought there was an
>> ambiguity here. The intention was for stub files to conform to the same
>> grammar as regular .py files, but with a different interpretation.
>>
>> > "Have the same syntax as regular Python modules" and "are files
>> containing type hints" are at odds with each other.
>>
>> That depends. *same syntax as regular Python* is normative while
>> *containing type hints* is an informal description of intent.
>>
>> I happen to be somewhat familiar with the situation that lead to this
>> question -- pytype has its own parser for stub files that cannot parse all
>> Python constructs. But claiming that PEP 484 is ambiguous feels wrong, and
>> if we really need to clarify it the only way to go is to make "same syntax
>> as regular Python" more clearly normative. Type checkers should of course
>> feel free ignore everything they don't care about.
>>
>
> I feel like the "same syntax as regular Python" is too broad a statement.
> That effectively requires a version specific Python interpreter to execute
> the files.  With at least four different Python static analyzers in
> existence today, keeping the behavior of all of them consistent is
> important.  Otherwise pyi files will be (are being) created that are
> analyzer specific and break other type checkers when distributed.
>

it doesn't require an interpreter, just a parser. Is saying it should be
syntactically valid Python 3.6 (though emphatically not executable!) still
too much?


> ex: We're encountering pyi files with conditional logic in them.  I
> believe we've encountered pyi files with del statements in them?  Both of
> these are a slippery slope towards being turing complete in something that
> isn't supposed to be code.  I don't like this.  Interface declarations
> should not contain logic.  If we allow conditions, we need to explicitly
> define what we do allow in the PEP.  (if+else and del?  what inputs are
> allowed for the expression in if statements?).  Otherwise at some point
> someone is going to create a pyi file containing loops, function calls, and
> generator expressions and expect it to _do_ something.  The horror!  Lets
> avoid that.
>

Syntactically, conditional logic *is* part of the spec because of
`sys.version_info` and `sys.platform` checks. These are mentioned in PEP
484 (though IIRC they were added at some point).

Feel free to ignore `del` statements, but they are valid syntax.


> PEP-484 does contain the text, "This also reinforces the notion that no
> runtime behavior should be expected of stub files." But reinforcing a
> notion is not what I read as a concrete statement.
>
> I'd rather see that say something like, "There must not be any runtime
> behavior from a stub file. They will be parsed for information, not
> executed."  Wordsmith that all you want, I'm not pedantic enough. :)
>

I don't see that as any more precise as what the PEP says. :-)

I'd be happy to claim that if the ast module can't parse a .pyi file, it's
invalid, otherwise it's valid, except that `# type:` comments are
significant and the ast module doesn't preserve those.


> I expect someone pedantic to happily point out that a def or class or
> assignment to ... with an annotation is runtime behavior... technically
> correct, but that isn't how people like me think of them in this context.
>

And mypy agrees. :-)


> We use a Pythonic syntax for stubs to be consistent with the language,
> that doesn't mean they are code.
>

Define "code". To some people HTML is code.


> I wrote more than I thought I would here, I'll stop now. :)
>

It would be nice if the pytype team could articulate the problems they're
trying to solve, rather than offering to "help finalize PEP 484". My guess
is that their parser for .pyi files only accepts a subset of Python and
they're (you're? do you report to Adam?) reluctant to sink more time in
that parser -- but I don't think that's my problem. :-)

My intention for stubs was exactly what I've been saying in this thread:
they must be syntactically valid Python, they are not meant to be executed,
and type checkers are free to ignore things they don't need. If that's not
sufficiently clear in the way the PEP is currently written, I welcome a PR
to the peps repo. If the pytype team wants a different interpretation, the
bar is much higher.

-- 
--Guido van Rossum (python.org/~guido)
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Re: [Python-Dev] Question about PEP 484

[Rebecca Chen via Python-Dev]

Hi Guido and all,

Let me try to clarify our (pytype team's) intentions a bit. Our
overall goal is to see PEP 484 finalized, in the interest of having a
definitive type-checking reference to point to and work off of. We're
willing and eager to help with this, if we get some guidance on what
the authors are still trying to finalize and how we can be useful. As
a conversation starter, we offered two issues in which pytype has some
personal stake.

Best,
Rebecca

P.S. Yes, Adam manages Python at Google.

On Mon, Jul 16, 2018 at 3:15 PM Guido van Rossum  wrote:
>
> On Mon, Jul 16, 2018 at 2:56 PM, Gregory P. Smith  wrote:
>>
>>
>> On Mon, Jul 16, 2018 at 1:44 PM Guido van Rossum  wrote:
>>>
>>> As one of the authors of PEP 484, *I* never thought there was an ambiguity 
>>> here. The intention was for stub files to conform to the same grammar as 
>>> regular .py files, but with a different interpretation.
>>>
>>> > "Have the same syntax as regular Python modules" and "are files 
>>> > containing type hints" are at odds with each other.
>>>
>>> That depends. *same syntax as regular Python* is normative while 
>>> *containing type hints* is an informal description of intent.
>>>
>>> I happen to be somewhat familiar with the situation that lead to this 
>>> question -- pytype has its own parser for stub files that cannot parse all 
>>> Python constructs. But claiming that PEP 484 is ambiguous feels wrong, and 
>>> if we really need to clarify it the only way to go is to make "same syntax 
>>> as regular Python" more clearly normative. Type checkers should of course 
>>> feel free ignore everything they don't care about.
>>
>>
>> I feel like the "same syntax as regular Python" is too broad a statement.  
>> That effectively requires a version specific Python interpreter to execute 
>> the files.  With at least four different Python static analyzers in 
>> existence today, keeping the behavior of all of them consistent is 
>> important.  Otherwise pyi files will be (are being) created that are 
>> analyzer specific and break other type checkers when distributed.
>
>
> it doesn't require an interpreter, just a parser. Is saying it should be 
> syntactically valid Python 3.6 (though emphatically not executable!) still 
> too much?
>
>>
>> ex: We're encountering pyi files with conditional logic in them.  I believe 
>> we've encountered pyi files with del statements in them?  Both of these are 
>> a slippery slope towards being turing complete in something that isn't 
>> supposed to be code.  I don't like this.  Interface declarations should not 
>> contain logic.  If we allow conditions, we need to explicitly define what we 
>> do allow in the PEP.  (if+else and del?  what inputs are allowed for the 
>> expression in if statements?).  Otherwise at some point someone is going to 
>> create a pyi file containing loops, function calls, and generator 
>> expressions and expect it to _do_ something.  The horror!  Lets avoid that.
>
>
> Syntactically, conditional logic *is* part of the spec because of 
> `sys.version_info` and `sys.platform` checks. These are mentioned in PEP 484 
> (though IIRC they were added at some point).
>
> Feel free to ignore `del` statements, but they are valid syntax.
>
>>
>> PEP-484 does contain the text, "This also reinforces the notion that no 
>> runtime behavior should be expected of stub files." But reinforcing a notion 
>> is not what I read as a concrete statement.
>>
>> I'd rather see that say something like, "There must not be any runtime 
>> behavior from a stub file. They will be parsed for information, not 
>> executed."  Wordsmith that all you want, I'm not pedantic enough. :)
>
>
> I don't see that as any more precise as what the PEP says. :-)
>
> I'd be happy to claim that if the ast module can't parse a .pyi file, it's 
> invalid, otherwise it's valid, except that `# type:` comments are significant 
> and the ast module doesn't preserve those.
>
>>
>> I expect someone pedantic to happily point out that a def or class or 
>> assignment to ... with an annotation is runtime behavior... technically 
>> correct, but that isn't how people like me think of them in this context.
>
>
> And mypy agrees. :-)
>
>>
>> We use a Pythonic syntax for stubs to be consistent with the language, that 
>> doesn't mean they are code.
>
>
> Define "code". To some people HTML is code.
>
>>
>> I wrote more than I thought I would here, I'll stop now. :)
>
>
> It would be nice if the pytype team could articulate the problems they're 
> trying to solve, rather than offering to "help finalize PEP 484". My guess is 
> that their parser for .pyi files only accepts a subset of Python and they're 
> (you're? do you report to Adam?) reluctant to sink more time in that parser 
> -- but I don't think that's my problem. :-)
>
> My intention for stubs was exactly what I've been saying in this thread: they 
> must be syntactically valid Python, they are not meant to be executed, and 
> type checkers are free to ignore th

Re: [Python-Dev] Question about PEP 484

[Guido van Rossum]

Thanks, Rebecca! So the status of PEP 484 is that we don't want to add new
features to it -- those require their own PEP. But we do accept PRs for
clarifications, assuming the clarifications are about issues where the
intention is clear but the text is not (usually because we thought there
was only one possible interpretation). If PEP 484 had intended to only
allow a specific subset of Python *syntax* we surely would have specified
that subset -- so I think the intention is clear (enough).

Unfortunately a lot of PEP 484 is written in the form of examples, and in
many cases it would be possible to quibble about edge cases not covered by
the examples. (An example that just came up: is `#type: foo` a valid type
comment? What about `#   type:foo`? Or `# < type: foo`? The intention was
`#\s*type:\s*` but all the PEP examples use exactly one space.)


On Mon, Jul 16, 2018 at 4:28 PM, Rebecca Chen  wrote:

> Hi Guido and all,
>
> Let me try to clarify our (pytype team's) intentions a bit. Our
> overall goal is to see PEP 484 finalized, in the interest of having a
> definitive type-checking reference to point to and work off of. We're
> willing and eager to help with this, if we get some guidance on what
> the authors are still trying to finalize and how we can be useful. As
> a conversation starter, we offered two issues in which pytype has some
> personal stake.
>
> Best,
> Rebecca
>
> P.S. Yes, Adam manages Python at Google.
>
> On Mon, Jul 16, 2018 at 3:15 PM Guido van Rossum  wrote:
> >
> > On Mon, Jul 16, 2018 at 2:56 PM, Gregory P. Smith 
> wrote:
> >>
> >>
> >> On Mon, Jul 16, 2018 at 1:44 PM Guido van Rossum 
> wrote:
> >>>
> >>> As one of the authors of PEP 484, *I* never thought there was an
> ambiguity here. The intention was for stub files to conform to the same
> grammar as regular .py files, but with a different interpretation.
> >>>
> >>> > "Have the same syntax as regular Python modules" and "are files
> containing type hints" are at odds with each other.
> >>>
> >>> That depends. *same syntax as regular Python* is normative while
> *containing type hints* is an informal description of intent.
> >>>
> >>> I happen to be somewhat familiar with the situation that lead to this
> question -- pytype has its own parser for stub files that cannot parse all
> Python constructs. But claiming that PEP 484 is ambiguous feels wrong, and
> if we really need to clarify it the only way to go is to make "same syntax
> as regular Python" more clearly normative. Type checkers should of course
> feel free ignore everything they don't care about.
> >>
> >>
> >> I feel like the "same syntax as regular Python" is too broad a
> statement.  That effectively requires a version specific Python interpreter
> to execute the files.  With at least four different Python static analyzers
> in existence today, keeping the behavior of all of them consistent is
> important.  Otherwise pyi files will be (are being) created that are
> analyzer specific and break other type checkers when distributed.
> >
> >
> > it doesn't require an interpreter, just a parser. Is saying it should be
> syntactically valid Python 3.6 (though emphatically not executable!) still
> too much?
> >
> >>
> >> ex: We're encountering pyi files with conditional logic in them.  I
> believe we've encountered pyi files with del statements in them?  Both of
> these are a slippery slope towards being turing complete in something that
> isn't supposed to be code.  I don't like this.  Interface declarations
> should not contain logic.  If we allow conditions, we need to explicitly
> define what we do allow in the PEP.  (if+else and del?  what inputs are
> allowed for the expression in if statements?).  Otherwise at some point
> someone is going to create a pyi file containing loops, function calls, and
> generator expressions and expect it to _do_ something.  The horror!  Lets
> avoid that.
> >
> >
> > Syntactically, conditional logic *is* part of the spec because of
> `sys.version_info` and `sys.platform` checks. These are mentioned in PEP
> 484 (though IIRC they were added at some point).
> >
> > Feel free to ignore `del` statements, but they are valid syntax.
> >
> >>
> >> PEP-484 does contain the text, "This also reinforces the notion that no
> runtime behavior should be expected of stub files." But reinforcing a
> notion is not what I read as a concrete statement.
> >>
> >> I'd rather see that say something like, "There must not be any runtime
> behavior from a stub file. They will be parsed for information, not
> executed."  Wordsmith that all you want, I'm not pedantic enough. :)
> >
> >
> > I don't see that as any more precise as what the PEP says. :-)
> >
> > I'd be happy to claim that if the ast module can't parse a .pyi file,
> it's invalid, otherwise it's valid, except that `# type:` comments are
> significant and the ast module doesn't preserve those.
> >
> >>
> >> I expect someone pedantic to happily point out that a def or class or
> assignment to ... w

[Python-Dev] Const access to CPython objects outside of GIL?

[Radim Řehůřek]

Hi all,

one of our Python projects calls for pretty heavy, low-level optimizations.

We went down the rabbit hole and determined that having access to
PyList_GET_ITEM(list), PyInt_AS_LONG(int) and PyDict_GetItem(dict, unicode)
on Python objects **outside of GIL** might be a good-enough solution. The
Python objects in question are guaranteed to live and not be mutated
externally in any way. They're "frozen" and read-only.

Under what conditions is it OK to call these 3 functions on such objects?

More generally, what is the CPython 2.7/3.5 contract regarding (lack of)
object mutation, and the need for reference counting and synchronization
via GIL?

Which C API functions are safe to call on "const" objects?

Obviously releasing GIL and then calling C API is hacky, but from initial
experiments, it seems to work (see
https://stackoverflow.com/questions/51351609/can-i-const-access-cpython-objects-without-gil).
But I'm wondering if there's a more formal contract around this behaviour.

Cheers,
Radim
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Re: [Python-Dev] Const access to CPython objects outside of GIL?

[Tim Peters]

[Radim Řehůřek ]

> one of our Python projects calls for pretty heavy, low-level optimizations.


> We went down the rabbit hole and determined that having access to
> PyList_GET_ITEM(list), PyInt_AS_LONG(int) and PyDict_GetItem(dict, unicode)
> on Python objects **outside of GIL** might be a good-enough solution. The
> Python objects in question are guaranteed to live and not be mutated
> externally in any way. They're "frozen" and read-only.
>
> Under what conditions is it OK to call these 3 functions on such objects?
>

>From the "initialization, Finalization, and Threads" section of the
Python/C API Reference Manual:

Therefore, the rule exists that only the thread that has acquired the GIL
> may operate on Python objects or call Python/C API functions.


Under protection of the GIL is the only documented - or intended - way to
do anything with Python objects, or to call virtually any Python/C API
function.



> More generally, what is the CPython 2.7/3.5 contract regarding (lack of)
> object mutation, and the need for reference counting and synchronization
> via GIL?
>

There is no intention to support GIL-free access to any Python objects.  So
that's the contract:  "All warranties are null & void if you do just about
anything while not holding the GIL".


> Which C API functions are safe to call on "const" objects?
>

None.  If you find some combinations of CPython versions, functions, and
objects, that happen to work, that's fine, but there's no guarantee they'll
continue to work, not even across maintenance releases.  Although they'll
_probably_ continue to work.

Obviously releasing GIL and then calling C API is hacky, but from initial
> experiments, it seems to work (see
> https://stackoverflow.com/questions/51351609/can-i-const-access-cpython-objects-without-gil).
> But I'm wondering if there's a more formal contract around this behaviour.
>

Nope!  You're on your own here.

Which doesn't mean you can't do it.  Just that if things blow up, you're
still on your own - since you're far outside what the documentation says is
required (which I suspect you knew before you asked ;-) ), the project
won't even accept a bug report.

If you want more help trying to guess which functions _may_ work outside
the law, that's fine too, but "python-dev" (this mailing list) is for
development _of_ Python itself, not for questions about _using_ Python.
The more general python-list would be more appropriate.  But, since you're
trying to use the C API in unsupported ways it wasn't intended to be used,
you'll likely have a hard time finding people with significant experience
doing the same thing.  Since it's not at all an intended use, there are no
"general principles" at work to ease the pain of staring at the CPython
source code to try to guess what might go wrong across all code paths.
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