[Python-Dev] signature object issues (to discuss while I am out of contact)

Mon May 1 20:40:31 CEST 2006

Brett Cannon wrote:
> The second question is whether it is worth providing a function that
> will either figure out if a tuple and dict representing arguments
> would work in calling the function. Some have even suggested a
> function that returns the actual bindings if the call were to occur. 
> Personally I don't see a huge use for either, but even less for the
> latter version. If people have a legit use case for either please
> speak up, otherwise I am tempted to keep the object simple.

One use case that comes to mind is a type-checking decorator (or 
precondition-checking decorator, etc):
@precondition(lambda x,y: x>y)
@precondition(lambda y,z: y>z)
def foo(x, y, z): ...
where precondition is something like:
def precondition(test):
 def add_precondition(func):
 def f(*args, **kwargs):
 bindings = func.__signature__.bindings(args, kwargs)
 if not test(**bindings):
 raise ValueError, 'Precontition not met'
 func(*args, **kwargs)
 return f
 return add_precondition
-Edward