[issue37923] Combining typing.get_type_hints and inspect.signature

[Larry Hastings]

Change by Larry Hastings :


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nosy:  -larry

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[issue37923] Combining typing.get_type_hints and inspect.signature

[Larry Hastings]

Larry Hastings  added the comment:

"Type hints" and "annotations" aren't the same thing.  And type hints are more 
opinionated about the values of annotations than would be appropriate for the 
inspect module.  For example, typing.get_type_hints() wraps strings with 
ForwardRef, turns None into NoneType, and it ignores objects with a 
"__no_type_check__" attribute.

So, I think it might be okay to *add* a *new* function to the typing module 
that was equivalent to inspect.signature() (and typing.signature() seems like a 
good name here).  I don't use type hints, so I don't have a strong opinion on 
that either way.  But you definitely shouldn't modify inspect.signature() so it 
produces type hints.

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[issue37923] Combining typing.get_type_hints and inspect.signature

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:

As of Python 3.10, thanks to Larry Hastings inspect.signature will have a new 
eval_str= parameter that lets you evaluate string annotations. This isn't quite 
what you're asking for, though, because typing.get_type_hints does more work 
than eval_str does. Still, it's similar enough that I'm inclined to close this 
issue.

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nosy: +Jelle Zijlstra, larry

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[issue37923] Combining typing.get_type_hints and inspect.signature

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

Somewhat related to https://bugs.python.org/issue37496

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nosy: +eric.snow, yselivanov

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[issue37923] Combining typing.get_type_hints and inspect.signature

[dmontague]

New submission from dmontague :

I am trying to obtain the output of `inspect.signature`, except with 
string-valued annotations converted to resolved type hints, similarly to 
`typing.get_type_hints`.

Is there a good way to do this currently? If not, might this be a good fit for 
the standard library?

---

The straightforward way I see to attempt this would be to call both 
`typing.get_type_hints` and `inspect.signature` on the callable, and then 
"merge" the results. However, as far as I can tell, that only works if the 
provided callable is a function or method (i.e., not a type or a callable class 
instance).

As an example, if I have an instance of a class with a `__call__` method, and 
the class was defined in a module with `from __future__ import annotations`, 
then calling `inspect.signature` on the instances will only return an 
`inspect.Signature` with type-unaware strings as the annotations for each 
`inspect.Parameter`. On the other hand, calling `get_type_hints` on the 
instance will return type hints for the class, rather than for its `__call__` 
method.

I wouldn't mind manually handling an edge case or two, but the logic used by 
`inspect.signature` to determine which function will be called seems relatively 
involved, and so I would ideally like to leverage this same logic while 
obtaining the type-resolved version signature for the callable.

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messages: 350248
nosy: dmontague, levkivskyi
priority: normal
severity: normal
status: open
title: Combining typing.get_type_hints and inspect.signature
type: enhancement
versions: Python 3.7

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