[Tutor] Re: Tutor Digest, Vol 2, Issue 2

[Danny Yoo]

On Tue, 2 Sep 2003, Brian Christopher Robinson wrote:

> Ok, this is what I put as a member of my TagSort class:
>
>      def __iter__(self):
>          return self.array.__iter__()
>
> Now, this is actually wrong since it doesn't take in to account the order
> of the TagArray.  But this doesn't even work at all.  Instead I get the
> message:
>
> AttributeError: 'list' object has no attribute '__iter__'
>
> What's that all about?


Hi Brian,


Odd; that should have worked... Ah.  Lists do have an __iter__ attribute
in Python 2.3:

###
>>> l = []
>>> l.__iter__
<method-wrapper object at 0x400e53ec>
###


But they don't appear to have one in 2.2:

###
>>> l = []
>>> l.__iter__
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: 'list' object has no attribute '__iter__'
###

It looks like the implementers did more polishing up of the class/type
stuff in Python 2.3; I didn't expect this not to work in 2.2!

But there's a way of writing it so it works with both:

    def __iter__(self):
        return iter(self.array)




> def tagSort(array):
>      copy = array[:] # copies the array
>      copy.sort()
>      indexes = []
>      for number in copy:
>          indexes.append(array.index(number))
>      return indexes
>
> Which works great.  My friend was opposed to the copy, though, so I
> wrote this:


There's a small bug here: it doesn't work if there are duplicates in our
original array:

###
>>> tagSort([1,1,1,1,1])
[0, 0, 0, 0, 0]
###


Instead of array.index(), we'd need to cook up our own function that uses
the 'is' operator instead of the '==' operator:

###
>>> "4" + "2" == "42"
1
>>> "4" + "2" is "42"
0
###



Talk to you later!