[Python-ideas] Proposal: Use mypy syntax for function annotations

[Stephen J. Turnbull]

Steven D'Aprano writes:

 > > 2) PEP 3107 only specifies arguments and return values but not
 > > exceptions that can be raised by a function. Java has the "throws"
 > > syntax to list possible exceptions:
 > > 
 > >  public void readFile() throws IOException {}
 > 
 > I understand that this is called a "checked exception" in Java. I also 
 > understand that they are hated and derided

Sure, but that's because it's hard for a human to guess what might
happen down in lower-level functions, let alone 3rd-party libraries
and the runtime -- and your program fails if you guess wrong.

Maybe the fact that type-checking is going to be optional mitigates
that.

I suspect it's not terrible useful, but another idea is to invert the
sense, i.e. say what exceptions the function believes it handles, and
therefore cannot be raised.

 > Perhaps with a few years of experience, we might be able to extend this 
 > to exceptions without making the same mistakes as Java's checked 
 > exceptions, but I wouldn't rush into it.

+1 to that!