[Edu-sig] Reversing dictionaries, closures, permutations etc.

[Kirby Urner]

> OTOH I believe in math you talk about the inverse function (e.g. tan
> <-> atan) and not the reverse function.  And my car has a reverse. :-)
> 

Yes, that further tips the scales in favor of inverse.

> > So is 2.4 mylist.reversed() something that returns a list,
> > vs. reverses it in place?  Is there a parallel mylist.sorted()?
> 
> No.  reversed() and sorted() are builtins; reversed() returns an
> iterator that iterates over a sequence in reverse; sorted() returns a
> new list that is sorted:
> 

So dir([]) will not show 'sorted' as a list method?  I should just go read
the PEP.

I have to keep reminding myself that Python ain't SmallTalk, and we have
built-in top-level functions that don't show up anywhere in the object
hierarchy as class or instance methods -- that bit me before when I tried to
see int(x) always in terms of some x.__int__() method.

E.g.

 >>> int('123')
 123

But:

 >>> '123'.__int__()

 Traceback (most recent call last):
   File "<pyshell#88>", line 1, in -toplevel-
     '123'.__int__()
 AttributeError: 'str' object has no attribute '__int__'

> >>> for i in reversed([1,2,3]): print i
> 

So that wouldn't extend to generators (which can be iterated over, but "in
reverse" would make no sense).  Again, I need to read the PEP.  Out of date
over here.

Looking forward to 2.4

Thanks for the preview!

Kirby