How to set signature for python callables manually

Question

I want to offer a code completion for my pybind11 modules using Jedi. Jedi evaluates the __signature__ of callables for its completion. For more information see: Jedi struggles with pybind11 modules. But pybind11 is currently not able to generate them: Set the text_signature attribute of callables

Is there a way to manually set the __signature__ of callables (especially functions) using the python interpreter after the pybind11 module has been loaded? Something like this:

pyModule.myFunc.__signature__ = *Do some magic here*

Are there maybe some tools that can generate the signature of python callables? There are lot of packages for creating functions dynamically at runtime whcich also create the signature. But this is not my use case.

Answer 1

I didn't test this with Jedi because it looks like a lot of work to reliable set up and reproduce, but maybe the following will work already.

The canonical way to inspect a callable's signature is the aptly named inspect.signature function. It relies on the magic __annotations__ attribute, which can be modified at runtime:

>>> from inspect import signature
>>> def foo(bar):
...     return True
... 
>>> signature(foo)
<Signature (bar)>  # empty signature
>>> import typing
>>> foo.__annotations__ = {'bar': typing.Union[bool, None], 'return': bool}
>>> signature(foo)
<Signature (bar: Union[bool, NoneType]) -> bool>   # now contains the info we added

Since __signature__ is not a standard field, it might be generated by Jedi, their issue description in the ticket you linked also implies that they'd prefer to leverage inspect.signature directly.