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.