In Python, you have to specify the type and not rely on inference

In TypeScript, if you do this:

 function canDo(maybe = false) { console.log(maybe) } canDo(123) 

it will complain, with

 Argument of type '123' is not assignable to parameter of type 'boolean | undefined'.(2345) 

That's because it infers argument maybe to be a boolean.

In Python, with mypy and ty it is not so. For example:

 def can_do(maybe = False): print(maybe) can_do(123) 

Neither ty or mypy will complain about this. Curious.

To "fix" the problem with ty and mypy you have to explicitly state the type, like this:

 def can_do(maybe: bool = False): print(maybe) can_do(123) 

Now, you'll get a warning on the can_do(123) which is

 Argument 1 to "can_do" has incompatible type "int"; expected "bool" [arg-type] 

I'm sure there's a good explanation for the design choice but I don't know it. For right now, I'm just trying to remember that TypeScript != Python-with-types and that if I want to be more certain of types, I can't rely on inference like I can in TypeScript.