In Python should we set Optional[str] = None in the argument list?

Question

My coworker said the code I wrote crashed recently and that was because in the function's argument list I did not specify Optional[str] = None. I only have Optional[str].

So basically my function looks like this:

def a(b: Optional[str]):
    if b is None:
        <do something>
    else:
        <do something>

I always thought default for Optional argument is None, so I did not specify the default value. It did not crash for me but crashed for my coworker, so I'm kinda confused.

My python version is >=3.

Answer 1

As mentioned in the above comments, Optional[str] is a type-hint to be used by IDEs and other static analysis tools, not a default argument. If you want to make a default argument such that you can call the function with a(), then you do need to add = None as you proposed. That could be a reasonable approach if you expect this function to be called with an omitted argument, but that will depend on your design and architecture.