functions which take functions

[Chris Angelico]

On Tue, Apr 10, 2012 at 11:36 PM, Kiuhnm
<kiuhnm03.4t.yahoo.it at mail.python.org> wrote:
> On 4/10/2012 14:29, Ulrich Eckhardt wrote:
>>
>> Am 09.04.2012 20:57, schrieb Kiuhnm:
>>>
>>> Do you have some real or realistic (but easy and self-contained)
>>> examples when you had to define a (multi-statement) function and pass it
>>> to another function?
>>
>>
>> Take a look at decorators, they not only take non-trivial functions but
>> also return them. That said, I wonder what your intention behind this
>> question is...
>>
>
> That won't do. A good example is when you pass a function to re.sub, for
> instance.

The most common case of such a thing is a structure walking utility.
For instance, a linked-list walker could be written as:

def walk(tree,func):
    node=tree.head
    while node:
        func(node.data)
        node=tree.sibling

This could equally reasonably be written with yield, though I'm not
sure that it's possible to write a recursive generator as cleanly (eg
to walk a binary tree). Perhaps the new "yield from" syntax would be
good here, but I've never used it. In any case, it's a classic use of
passing a function-like as a parameter, even if there's another way to
do it.

ChrisA