[issue44791] Substitution of ParamSpec in Concatenate

[Mehdi2277]

Mehdi2277  added the comment:

Concatenate[int, ...] I would interpret as a function signature with first 
argument int, followed by arbitrary arguments afterwards. I haven't run into 
this case, but ... is allowed in other spots Paramspec is allowed currently.

P = Paramspec("P")

class Foo(Generic[P]):
  ...

Foo[...] # Allowed 
Callable[..., None] # Allowed

Are there any other places a paramspec is allowed? Generic type argument, first 
argument to callable, last to concatenate, anything else?

I'm unaware of any type checking use case for Concatenate[int, ...]. You can 
practically get same thing by using a paramspec variable without using it 
elsewhere so that it captures, but then effectively discards that information.

def use_func1(f: Callable[Concatenate[int, P], None]) -> None:
  ...

def use_func2(f: Callable[Concatenate[int, ...], None]) -> None:
  ...

feels like those two signatures should encode same information.

--
nosy: +med2277

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:

I'm looking at https://github.com/python/cpython/pull/30969 and I'm not sure 
what the motivation for the change is. PEP 612 is quite precise here 
(https://www.python.org/dev/peps/pep-0612/#id1) and allows only a ParamSpec as 
the last argument to Concatenate.

What is the use case for using ... as the last argument? What should it mean to 
a static type checker?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Marc Mueller]

Change by Marc Mueller :


--
nosy: +cdce8p

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Alex Waygood]

Change by Alex Waygood :


--
nosy: +sobolevn

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Alex Waygood]

Change by Alex Waygood :


--
nosy: +AlexWaygood

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Guido van Rossum]

Guido van Rossum  added the comment:

Before you start supporting things that contradict PEP 612 this should be 
discussed on typing-sig (or in the python/typing tracker).

Honestly I'd feel more comfortable if there was agreement on typing-sig with 
your previous PRs in this issue as well; "it does not contradict it" is not a 
ringing endorsement. :-)

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

PR 27518 fixes a substitution of a ParamSpec variable with a Concatenate nad a 
list of types. It is not specified explicitly in PEP 612, but it does not 
contradict it.

PR 30969 makes an ellipsis be valid as the last argument of Concatenate to fix 
a substitution of a ParamSpec variable with an ellipsis. It contradicts with 
PEP 612 which allows only a ParamSpec variable there.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
pull_requests: +29147
pull_request: https://github.com/python/cpython/pull/30969

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Jelle Zijlstra]

Change by Jelle Zijlstra :


--
nosy: +Jelle Zijlstra

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[miss-islington]

miss-islington  added the comment:


New changeset 89db09029566cf3af04b540e33fe1ff9b32f8c8b by Miss Islington (bot) 
in branch '3.10':
bpo-44791: Fix substitution of ParamSpec in Concatenate with different 
parameter expressions (GH-27518)
https://github.com/python/cpython/commit/89db09029566cf3af04b540e33fe1ff9b32f8c8b


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:


New changeset ecfacc362dd7fef7715dcd94f2e2ca6c622ef115 by Serhiy Storchaka in 
branch 'main':
bpo-44791: Fix substitution of ParamSpec in Concatenate with different 
parameter expressions (GH-27518)
https://github.com/python/cpython/commit/ecfacc362dd7fef7715dcd94f2e2ca6c622ef115


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[miss-islington]

Change by miss-islington :


--
nosy: +miss-islington
nosy_count: 3.0 -> 4.0
pull_requests: +29138
pull_request: https://github.com/python/cpython/pull/30959

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
keywords: +patch
pull_requests: +26033
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/27518

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

My understanding is that type expression is valid when substitute TypeVar and 
parameters expression is valid when substitute ParamSpec.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Ken Jin]

Ken Jin  added the comment:

Should Concatenate support substitution to begin with? PEP 612 doesn't say 
anything, and I am fairly certain it's a special typing form, not a generic. So 
I don't really understand what it means to substitute Concatenate.

Then again, Callable with a nested Concatenate can be substituted, and we 
currently implement that by using Concatenate's substitution behavior as proxy. 
But again, the meaning isn't clear to me.

I also noticed this strange part in PEP 612 about user-defined generic classes:

"`Generic[P]` makes a class generic on `parameters_expressions` (when P is a 
ParamSpec)":

...
class X(Generic[T, P]):
  f: Callable[P, int]
  x: T

def f(x: X[int, Concatenate[int, P_2]]) -> str: ...  # Accepted (KJ: What?)
...

The grammar for `parameters_expression` is:

parameters_expression ::=
  | "..."
  | "[" [ type_expression ("," type_expression)* ] "]"
  | parameter_specification_variable
  | concatenate "["
   type_expression ("," type_expression)* ","
   parameter_specification_variable
"]"

I'm very confused. Does this mean Concatenate is valid when substituting user 
generics? Maybe I should ask the PEP authors?

My general sense when I implemented the PEP was that it was intended primarily 
for static type checking only. IMO, runtime correctness wasn't its concern.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue44791] Substitution of ParamSpec in Concatenate

[Serhiy Storchaka]

New submission from Serhiy Storchaka :

Substitution of ParamSpec in Concatenate produces weird results:

>>> import typing
>>> P = typing.ParamSpec('P')
>>> typing.Concatenate[str, P][int]
typing.Concatenate[str, int]
>>> typing.Concatenate[str, P][[int]]
typing.Concatenate[str, (,)]
>>> typing.Concatenate[str, P][typing.Concatenate[int, P]]
typing.Concatenate[str, typing.Concatenate[int, ~P]]

But all these results are invalid:

>>> typing.Concatenate[str, int]
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
return func(*args, **kwds)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 400, in __getitem__
return self._getitem(self, parameters)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 595, in Concatenate
raise TypeError("The last parameter to Concatenate should be a "

TypeError: The last parameter to Concatenate should be a ParamSpec variable.
>>> typing.Concatenate[str, (int,)]
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
return func(*args, **kwds)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 400, in __getitem__
return self._getitem(self, parameters)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 595, in Concatenate
raise TypeError("The last parameter to Concatenate should be a "

TypeError: The last parameter to Concatenate should be a ParamSpec variable.
>>> typing.Concatenate[str, [int]]
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
return func(*args, **kwds)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 400, in __getitem__
return self._getitem(self, parameters)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 595, in Concatenate
raise TypeError("The last parameter to Concatenate should be a "

TypeError: The last parameter to Concatenate should be a ParamSpec variable.
>>> typing.Concatenate[str, typing.Concatenate[int, P]]
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
return func(*args, **kwds)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 400, in __getitem__
return self._getitem(self, parameters)
   ^^^
  File "/home/serhiy/py/cpython/Lib/typing.py", line 595, in Concatenate
raise TypeError("The last parameter to Concatenate should be a "

TypeError: The last parameter to Concatenate should be a ParamSpec variable.

I expect that

1. The last parameter to Concatenate can be a Concatenate. Inner Concatenate 
should merge with the external one:

Concatenate[str, Concatenate[int, P]] -> Concatenate[str, int, P]
Concatenate[str, P][Concatenate[int, P]] -> Concatenate[str, int, P]

2. The last parameter to Concatenate can be a list of types. The result should 
be a list of types.

Concatenate[str, [int, dict]] -> [str, int, dict]
Concatenate[str, P][[int, dict]] -> [str, int, dict]

3. The last parameter to Concatenate can be an ellipsis.

Concatenate[str, ...]
Concatenate[str, P][...] -> Concatenate[str, ...]

--
components: Library (Lib)
messages: 398632
nosy: gvanrossum, kj, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Substitution of ParamSpec in Concatenate
versions: Python 3.10, Python 3.11

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com