[Tutor] Function in a data structure

[Rodrigues]

> -----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

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,))
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