Optional Static Typing

[Michael Hobbs]

Rahul <codedivine at gmail.com> wrote:
> I am assuming that optional type checking is being added for easier
> debugging only. So if 'expects' are turned on , python raises
> warnings(which do not halt the system) but not when they are turned
> off. These will enable easier debugging for new people while not
> affecting masters. Also,perhaps, it will be easier to accomodate till
> type checking mechanism is perfected(if it is implemented at all that
> is) so that python does not stop you when it is in fact  python which
> might be making some mistake.(This last statement is a guess only...)
> 
> It is similar to assert and __debug__=1 in a way.
> 
> So the crux is :
> 1.Expects is only a bridge between type checking and dynamic typing.
> 2.Type checking is done only as a tool which you are free to override
> if you want to.
> 3.The objective of type checking here is only to make debugging easier
> and not speed/optimization.
> 4.The point is not that 'expects' be a additional keyword.You can go
> like this also :
> def (int a,int b): or whatever you like. Only that expects make it a
> bit clearer IMHO.
> 
> sincerely.,
> rahul

Your proposition reminds me very much of Design by Contract, which is
a prominent feature of the Eiffel programming language. Considering
that Python is an interpreted language where type checking would
naturally occur at runtime, I think Design by Contract would be more
appropriate than static typing.

In a function's contract, not only could it state that its parameter
must be an integer, but also that it must be > 50 and be divisible by
7. If a value is passed to the function that violates the contract,
it raises an exception.

In Eiffel, contract checking can be turned on or off based on a 
compiler flag or a runtime switch.

- Mike