Incorrect inspect.Signature can be created: pos-only with a default followed by pos-or-kw without one #103556
Description
While working on #103553 I found one more problem that merits its own issue.
Right now it is impossible to create a function that have a pos-or-keyword parameter without a default comming after a pos-only parameter with a default. Demo:
>>> def test(pod=42, /, pk): ...
File "<stdin>", line 1
def test(pod=42, /, pk): ...
^^
SyntaxError: parameter without a default follows parameter with a default
>>> lambda pod=42, /, pk: ...
File "<stdin>", line 1
lambda pod=42, /, pk: ...
^^
SyntaxError: parameter without a default follows parameter with a defaultBut, it is possible to create a signature like this. Repro:
>>> import inspect
>>> def one(pk): ...
...
>>> def two(pod=42, /): ...
...
>>> sig1 = inspect.signature(one)
>>> sig2 = inspect.signature(two)
>>> inspect.Signature((sig2.parameters['pod'], sig1.parameters['pk']))
<Signature (pod=42, /, pk)>This looks like a bug to me, there's no reason for a signature to behave differently and to support function signatures that cannot be created.
Desired behaviour:
Traceback (most recent call last):
File "/Users/sobolev/Desktop/cpython/ex.py", line 7, in <module>
print(inspect.Signature((sig2.parameters['pod'], sig1.parameters['pk'])))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/sobolev/Desktop/cpython/Lib/inspect.py", line 3039, in __init__
raise ValueError(msg)
ValueError: non-default argument follows default argumentThe fix is quite easy. PR is incomming.
I've also tried the same thing with #103404 (because it is very related) but, it still does not solve this corner case.