On Wed, Aug 13, 2014 at 10:29:48PM +0200, Christian Heimes wrote:
1) I'm not keen with the naming of mypy's typing classes. The visual distinction between e.g. dict() and Dict() is too small and IMHO confusing for newcomers. How about an additional 'T' prefix to make clear that the objects are referring to typing objects?
from typing import TList, TDict
def word_count(input: TList[str]) -> TDict[str, int]: ...
Would it be possible, and desirable, to modify the built-in types so that we could re-use them in the type annotations? def word_count(input: list[str]) -> dict[str, int]: Since types are otherwise unlikely to be indexable like that, I think that might work.
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 as useless or even counter-productive: http://literatejava.com/exceptions/checked-exceptions-javas-biggest-mistake/
May I suggest that we also standardize a way to annotate the exceptions that can be raised by a function? It's a very useful piece of information and commonly requested information on the Python user mailing list.
And as frequently explained on the python-list, it's almost impossible to answer. Or rather, the answer is usually no more specific than "raises Exception". There are very few guarantees you can reliably make about what exceptions *cannot* be raised by a function. To put it simply, given almost any operation in your function, say, x+1, there's no limit on what x.__add__ might raise. Even if you know x is a subclass of int, it could do anything in its __add__ method. Only if you know x is *exactly* a builtin int can you be confident that it won't raise (say) ImportError. 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. -- Steven