Contracts

[senko]

Should we support contracts?

It would be straightforward to support contracts by supporting custom callables in type signatures. For example:

@params(a=int, b=lambda b: b != 0)
def div(a, b):
    return a / b

However, I find that syntax clunky (for contracts), compared to something like:

@contract
def div(a, b):
    return a / b

@div.requires
def div(a, b):
    assert isinstance(a, int)
    assert b != 0

But this being typedecorator, not a full-blown contracts library, I'm hesitant to grow it in that direction (unless there's popular demand).

[senko]

Another problem with this approach: typedecorator by default raises TypeError (in any case, a single exception class), but with contracts it makes sense to return ValueError (or at least something different to TypeError) if contracts are violated.

This would mean we'd have to support raising various exceptions based on the type of type/constraint violation, which would make the code more convoluted.