UI text when hovering over a variable whose type is a callable Protocol

[aholmes]

References

With reference to Python 3.10 as a minimum version.

When type-hinting callables, we run into limitations and need workarounds. For example, a type I will refer to has the signature (config: Config, request_context_args: dict[Any, Any] | None = None) -> RequestContext.

Please reference this code.

Using Callable:

FlaskRequestConfigurable = Callable[[Config, dict[Any, Any] | None], RequestContext]

Using Protocol:

class FlaskRequestConfigurable(Protocol):
   def __call__(
       self, config: Config, request_context_args: dict[Any, Any] | None = None
   ) -> RequestContext:
       ...

Using either type as a paramter:

class test_foo(flask_request_configurable: FlaskRequestConfigurable):
    pass

Using either type as a variable:

flask_request_configurable: FlaskRequestConfigurable

Real code examples can be found here and here.

The Problem

With Callable, we can almost represent this as Callable[[Config, dict[Any, Any] | None], RequestContext]. We run into three issues:

• Callable does not allow parameter names
• Callable does not allow default parameter values
• At call sites, positional arguments only are expected and named-parameters raise type errors

However, one advantage with Callable is in how Pylance displays information about it when hovering over the type:

Common advice to work around the issues mentioned is to specify a Protocol class and the __call__ method. Indeed this does fix the issues, however, the UI experience is degraded.

And in fact the UI experience when hovering over a parameter (specifically) whose type is the callable is less than ideal in both scenarios.

Interestingly, I just noticed that a variable whose type is Callable is not displayed the same way as a parameter. This is not true with the Protocol workaround, which does display the same as when used as a parameter.

The Desired Enhancement

When a variable or parameter is a Protocol type with __call__ defined, and when hovered over or otherwise displaying information about the variable or parameter, showing the full call signature would make its purpose and usage more obvious. Ideally this would look similar, if not identical, to when the variable or parameter is a function:

[rchiodo]

Seems reasonable to me. Protocol derived Classes should be represented like a function in the UI, not a class. Or maybe at least show extra information considering they're protocols.