[Tutor] Function in a data structure

[Tim Johnson]

Hello Rodgrigues:

* Rodrigues <op73418@mail.telepac.pt> [030623 17:32]:
> > -----Original Message-----
> > From: tutor-admin@python.org
> > [mailto:tutor-admin@python.org]On Behalf Of
> > Tim Johnson
> >
> >
> > Hello All:
> >     I'd like to put a function in data structure
> >     and execute it as part of processing the
> >     structure.
> > I have
> > >>fd = {'func':[lambda x: x**2]}
> >
> 
> Here you a have a dictionary with one pair. The key is the string
> 'func', but the value is a *list* of one element, precisely the
> function object lambda x: x**2. Ditch the [] and your code below will
> (almost) work.
> 
> > How may I execute the lambda statement which
> > is the value for fd['func']?
> > I've tried:
> >   apply(fd['func'],(2))
> >   and apply(fd['func'],2)
> >   with no luck
 
  I have found that I can call this function with 
  >>> fd['func'][0](2)
  4
  :-) Works for me. But I am still intrigued by your
      solution with apply, but do not follow completely.
      Please excuse my newbie-lack-of-insite here.

> You are not using apply correctly. Firing an interactive prompt:
> 
> >>> help(apply)
> Help on built-in function apply:
> 
> apply(...)
>     apply(object[, args[, kwargs]]) -> value
> 
>     Call a callable object with positional arguments taken from the
> tuple args,
>     and keyword arguments taken from the optional dictionary kwargs.
>     Note that classes are callable, as are instances with a __call__()
> method.
> 
> >>>
> 
> So what you need is:
> 
> >>> apply(lambda x:x**2, (2,))

 Rodrigues, you are using apply without referencing
 the 'lambda' statement from my original dictionary
 example. So I am still unclear on how you would use
 apply to execute the 'lambda' as a member of the
 dictionary. Sorry to be so dense, but maybe I
 shouldn't try to cook dinner and code at the same
 time.

  I find that apply(fd['func'][0],(2,)) also
  works, is this what you meant?

 Many thanks!
 tim
> 4
> 
> Notice the use of (2,) instead of just (2), to build a tuple of one
> element only.
> 
> By the way, apply is being deprecated, you should be using the *, **
> syntax. A simple example should explain how it works:
> 
> >>> func = lambda x:x**2
> >>> args = (2,)
> >>> func(*args)
> 4
> 
> Hope it helps, with my best regards
> G. Rodrigues
> 
> 
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-- 
Tim Johnson <tim@johnsons-web.com>
      http://www.alaska-internet-solutions.com
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