self-promotion of the decorator module (Was: How to learn OO of python?)

[Michele Simionato]

could ildg wrote:

> I think decorator is a function which return a function, is this
right?
> e.g. The decorator below if from
http://www.python.org/peps/pep-0318.html#id1.
>
> def accepts(*types):
>     def check_accepts(f):
>         assert len(types) == f.func_code.co_argcount
>         def new_f(*args, **kwds):
>             for (a, t) in zip(args, types):
>                 assert isinstance(a, t), \
>                        "arg %r does not match %s" % (a,t)
>             return f(*args, **kwds)
>         new_f.func_name = f.func_name
>         return new_f
>     return check_accepts
>
> After I saw all the examples, I concluded that every decorator must
> define an inner function which takes only one argument, the
> function to decorate. Is this right?
>

Yes, but you may want to look at my decorator module:

http://www.phyast.pitt.edu/~micheles/python/decorator.zip

Your example would be written as follows:

from decorator import decorator

def accepts(*types):
    def check_accepts(f, *args, **kw):
        assert len(types) == f.func_code.co_argcount
        for a, t in zip(args, types):
            assert isinstance(a, t), "arg %r does not match %s" % (a,t)
        return f(*args, **kw)
    return decorator(check_accepts)

with the following advantages:

1. one-level of nesting is saved ("flat is better than nested")
2. name, docstring and dictionary of the original function are
    preserved;
3. the signature of the original function is preserved (this one is
nontrivial).


              Michele Simionato