[Edu-sig] Scratch pad nuttiness... (re generators)

[John Zelle]

Hi Kirby,

I happen to be working through some Python3.0 issues right now. A couple 
comments:

On Monday 16 March 2009 10:42:24 kirby urner wrote:
>
> So then it occurs to me, would there by a way to do a kind of special
> names overloading such that __next__ (that which triggers the next
> cycling to yield) might be replaced with the word kick in some
> namespace, as in kick(o) instead of next(o) -- using Python 3.x syntax
> here i.e. not o.next().
>
> What would a student try, if this were the challenge?
>
> Simple solution:
> >>> def kick(o):
>
> 	return next(o)

Of couse, the simplest solution is just to bind kick to next:

>>> o = iter(range(10))
>>> kick = next
>>> kick(o)
0
>>> kick(o)
1

That does the trick.

> >>> def f():  # could use a generator expression
>
> 	for i in range(10):
> 		yield i
>
> >>> type(f)  # just a function so far
>
> <class 'function'>
>
> >>> o = f()
> >>> next(o)
>
> 0
>
> >>> kick(o)
>
> 1
>
> >>> kick(o)
>
> 2
>
> >>> type(o)  # a generator once instanced
>
> <class 'generator'>
>
> Another student might think different and try something like this:
> >>> o.__next__
>
> <method-wrapper '__next__' of generator object at 0x8367edc>
>
> >>> o.kick = o.__next__
>
> Traceback (most recent call last):
>   File "<pyshell#51>", line 1, in <module>
>     o.kick = o.__next__
> AttributeError: 'generator' object has no attribute 'kick'
>
> "Dang, you can't give your generator object a random attribute i
> doesn't already have, write-protected in some way...."

Of course, even if this worked, it wouldn't give you the kick(o) behavior that 
you specified above. I could see where one might try this to get the 2.xish 
o.kick() behavior. Of course, you could easily get an alias to o's __next__ 
via simple assignment again:

>>> o = iter(range(10))
>>> kicko = o.__next__
>>> kicko()
0
>>> kicko()
1

> Note that the generator type is inappropriate as a base class for your
> own kind of user class.
>
> >>> class newgen (type(o)):
>
> 	kick = type(o).__next__
>
>
> Traceback (most recent call last):
>   File "<pyshell#10>", line 1, in <module>
>     class newgen (type(o)):
> TypeError: type 'generator' is not an acceptable base type

I don't follow the reasoning in this attempt at all.

--John