[Python-ideas] Before and after the colon in funciton defs.

[ron adam]

On Wed, 2011-09-21 at 11:34 -0700, Guido van Rossum wrote:
> When you say "compile time", do you literally mean "when the compiler
> creates the bytecode" or do you really intend this to be computed at
> function definition time (the same time when default values are
> evaluated)? The latter seems to make more sense.
> 
> --Guido

Yes, I meant at definition time. :-)



> On Wed, Sep 21, 2011 at 11:12 AM, Ron Adam <ron3200-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org> wrote:
> > On Wed, 2011-09-21 at 15:19 +1000, Nick Coghlan wrote:
> >
> >> Perhaps a non-syntax way to approach both of these would be to add a
> >> new decorator to 'functools':
> >>
> >>     def closure(f):
> >>         """Invokes the decorated function and returns the result after
> >> transcribing essential function metadata
> >>
> >>            This can be used to easily share algorithm state and get
> >> early binding semantics for names.
> >>         """
> >>         impl = f()
> >>         impl.__name__ = f.__name__
> >>         doc = f.__doc__
> >>         if doc is not None:
> >>             impl.__doc__ = doc
> >>         impl.__dict__.update(f.__dict__)
> >>         return impl
> >>
> >> This would be used as follows:
> >>
> >>     @functools.closure
> >>     def adder(i=i): # 'impl' defines call time signature
> >>         "Increments 'x' by adder.value"
> >>         def impl(x):
> >>             impl.call_count += 1
> >>             return x + i
> >>         impl.value = i
> >>         impl.call_count = 0
> >>         return impl
> >>
> >> >>> adder.value
> >> 10
> >> >>> adder(1)
> >> 11
> >> >>> adder(5)
> >> 15
> >> >>> adder(10)
> >> 20
> >> >>> adder.call_count
> >> 3
> >
> > Simplifying things like this is one of the use cases of allowing define
> > time statements.  That's a lot of work to just avoid putting a keyword
> > in the signature.  And it's not easy to understand.
> >
> > Decorators could be a good way to do this, but the problem in these
> > cases, is the function object doesn't have the needed support to make
> > things like this easy.
> >
> >
> > Probably the easiest and most direct way, would to be to add a new
> > keyword 'static' as MRAB suggested, but have it be an expression instead
> > of a command.
> >
> > value = (static <expression>)
> >
> >
> > def adder(x):
> >    return x + (static i)    # evaluate (static i) at compile time.
> >
> > The parentheses would be optional.
> >
> > The (static i) expression, could be spelled (i=i).  I think that was
> > what Guido was suggesting, but not as an expression.  As an expression,
> > you would then see things like.. i = (i=i).  But that may only be poor
> > style, because it's easy enough to just not do that.
> >
> > I think the expression form is better myself, it allows you to get both
> > the compile time value, and the current value of an identifier.
> >
> >
> > def value elapsed_frames():
> >    """ Where f is the frame counter in the parent scope. """
> >    return f - (static f)
> >
> >
> > Cheers,
> >   Ron
> >
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> > http://mail.python.org/mailman/listinfo/python-ideas
> >
> 
> 
>