scoping weirdness

Alex Martelli aleax at aleax.it
Mon Aug 27 12:06:21 CEST 2001


"Tim Peters" <tim.one at home.com> wrote in message
news:mailman.998804559.5680.python-list at python.org...
    ...
> >     def press_button (text):
> >       print 'you pressed %s' % text
> >
> >     def create_button (label):
> >       func = lambda: press_button (label)
> >       Button(root,text=label,command=func).pack()
> >       # if I put more stuff here and set label to something new,
> >       # the button doesn't do what I expected.
    ...
> Pick one:
    [snipped 5 ways to curry without calling it currying:-)]

Or pick another (explicit currying), e.g. with
"from __future__ import nested_scope" if need be:

def curry_to_argumentlessness(*args, **kwds):
    def totally_curried_function():
        return args[0](*args[1:],**kwds)
    return totally_curried_function

then use it at will, e.g.:


    def create_two_buttons(label):
        Button(root, text=label, command=
            curry_to_argumentlessness(press_button, label)
          ).pack()
        label = label.upper()
        Button(root, text=label, command=
            curry_to_argumentlessness(press_button, label)
          ).pack()

Currying-to-argumentlessness is a frequent enough need
(since Tk &c all want lots of argumentless callables)
that one may want to rename 'curry_to_argumentlessness'
to something more concise and put it in sitecustomize
or thereabouts.  Hmmm, there's lot of good currying stuff
already on the Cookbook, but presented in a much more
general way - I'm wondering if this extremely frequent
special case warrants its own recipe...


Alex






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