PEP 3107 and stronger typing (note: probably a newbie question)

[Paul Rubin]

Bruno Desthuilliers <bdesth.quelquechose at free.quelquepart.fr> writes:
> > Some users in fact recommend writing an explicit type signature for
> > every Haskell function, which functions sort of like a unit test.
> 
> Stop here. explicit type signature == declarative static typing !=
> unit test.

The user-written signature is not a declaration that informs the
compiler of the type.  The compiler still figures out the type by
inference, just as if the signature wasn't there.  The user-written
signature is more like an assertion about what type the compiler will
infer.  If the assertion is wrong, the compiler signals an error.  In
that sense it's like a unit test; it makes sure the function does what
the user expects.

> I have few "surprises" with typing in Python. Very few. Compared to
> the flexibility and simplicity gained from a dynamism that couldn't
> work with static typing - even using type inference -, I don't see it
> a such a wonderful gain. At least in my day to day work.

I'm going to keep an eye out for it in my day-to-day coding but I'm
not so convinced that I'm gaining much from Python's dynamism.
However, that may be a self-fulfilling prophecy since maybe I'm
cultivating a coding style that doesn't use the dynamism, and I could
be doing things differently.  I do find since switching to Python 2.5
and using iterators more extensively, I use the class/object features
a lot less.  Data that I would have put into instance attributes on
objects that get passed from one function to another, instead become
local variables in functions that get run over sequences, etc.