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inspect.Parameter checks that name is an identifier, but does not check for keywords #92062
Description
Consider the following code:
def send(from):
...This parses, but it doesn't compile: from is a keyword and so the code is syntactially invalid.
The problem is that inspect.Parameter checks that the given name is an identifier, but doesn't check that it's not a keyword. You can thus create invalid signatures, which cause considerable confusion on downstream introspection:
def f(source):
pass
from inspect import Signature, Parameter
f.__signature__ = Signature([Parameter("from", P.KEYWORD_ONLY)], return_annotation=None)
# Or, as the real-world motivation,
class Model(pydantic.BaseModel):
source: None = pydantic.Field(None, alias="from")We're fixing this downstream in HypothesisWorks/hypothesis#3317 and pydantic/pydantic#4012, but I think that inspect.Parameter("from", ...) should also raise an error, just as if the provided name was not an identifier at all.
Activity
pythongh-92062: reject keyword parameter names
JelleZijlstra commentedon Apr 30, 2022
I can see a scenario where this will break things: we try to get the signature for a function implemented in C that takes a positional-only argument with a name that happens to be a keyword. I can't find any instances of that pattern in typeshed or CPython, but they may exist elsewhere.
Zac-HD commentedon Apr 30, 2022
Hmm, that makes sense. I'll tighten the check to only apply if the
kind is not P.POSITIONAL_ONLY, since I don't expect this to weaken it as a check on Python code 👍pythongh-92062: allow pos-only keyword names
Zac-HD commentedon May 2, 2022
I think we're fine to continue ignoring unicode names which normalize to keywords, since that's the existing behaviour of
keyword.iskeywordand does actually work at runtime:gh-92062: `inspect.Parameter` checks whether `name` is a keyword (GH-…