Quick Fix Add "Optional" to Type Annotation doesn't work

[Molkree]

Environment data

• Language Server version: v2021.9.3
• OS and version: Win10, 19043.1237
• Python version (& distribution if applicable, e.g. Anaconda): 3.9.7

Expected behaviour

Quick Fix wraps function parameter type in Optional.

Actual behaviour

This is with strict type checking. None is underlined with this error:

Expression of type "None" cannot be assigned to parameter of type "int"
  Type "None" cannot be assigned to type "int" Pylance(reportGeneralTypeIssues)

When trying to apply Quick Fix nothing happens.

Code Snippet / Additional information

def foo(arg: int = None):
    print(arg)

[jakebailey]

I debugged this, and this one's just a bug where we seemingly have forgotten to include the name of the file to edit on the quick fix.

The fix is simple, but will take a little more than a line thanks to some plumbing to get a URI to the right place.

[yvvt0379]

But what about an argunent that starts life as None and stays not-None once assigned not-None object?

[erictraut]

I'm not sure what you mean. Can you provide a concrete example? I presume you're talking about a parameter, not an argument? (An argument is a value passed to a function, whereas a parameter is the name of an input used within a function.)

[yvvt0379]

Sorry to make you confused. Here's an example:

def func(lst: list[int], start: int = 0, end: int = None):
    if end is None:
        end = len(lst)
    # end shouldn't be None here
    ...

In this case, we don't want end to be None. What I worry about is that if we declare end as Optional[int], the code may not be robust enough.

[jakebailey]

I don't really know what the above has to do with the code action being broken; if you don't want to apply the code action, you don't have to. But, in the case above, if you type end as Optional[int], the code that assigns over end with an int if it's None will mean further uses are narrowed to int anyway. If that's not how it's behaving now, that sounds like a bug to me.

[yvvt0379]

Ok, thank u, I understand.

[jakebailey]

This issue has been fixed in version 2021.9.4, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202194-29-september-2021