Comments on: Iterators, Iterables, and Generators! Oh, my!

By: Sumudu Fernando

Sumudu Fernando — Fri, 27 Jan 2012 09:43:42 +0000

@spititan: Your example works, but the language does require iterators to implement __iter__. What you have defined is almost an iterator, but technically isn’t one. The reason this requirement exists is that it makes it easy to write functions that can accept either an iterable or an iterator, the same way that built-ins such as sum can.

More precisely, if we write a loop like:

for x in iter(foo):
pass

then foo can be either an iterable or an iterator.

One thing about the examples in the article is that they are slightly more complicated than necessary. For example, I would write:

def forward(self):
for c in self.data:
yield ord(c)

and

def reverse(self):
for c in reversed(self.data):
yield ord(c)

(though maybe the reversed built-in did not exist when the article was written)

By: spititan

spititan — Fri, 22 Apr 2011 00:05:39 +0000

This is a good article, but I just want to point out that a few things in this article is actually a bit misleading.

An iterator actually does not need to have an __iter__ method. next() is the only required method. The ‘in’ operator of Python actually calls __iter__ method on an iterable, then call next() method on the returned iterator.

See the following example code

#!/usr/bin/python2.6

class ByteValue(object):
def __init__(self, data):
self.data = data

class Iterator(object):
def __init__(self, data):
self.data = data
self.index = 0

def next(self):
if self.index == len(self.data):
raise StopIteration
else:
byte_value = ord(self.data[self.index])
self.index += 1
return byte_value

def __iter__(self):
return ByteValue.Iterator(self.data)

bv = ByteValue(“abcdefg”)
for byte_value in bv:
print(byte_value)

for byte_value in bv:
print(byte_value)

In this example, ByteValue is interable, the iterator for him is ByteValue.Iterator, which does not have __iter__ method.

By: Matt Thiessen

Matt Thiessen — Fri, 17 Dec 2010 17:53:12 +0000

A good explanation and examples of iterator of a class. Helped me solve my issue. Thanks

By: selsine

selsine — Tue, 23 Feb 2010 21:10:48 +0000

Hi Henry,

Thanks for the kind words. I’m trying to resume blogging as best I can but a one moth old eats up a lot of free time! Not to mention moving cities and a new house!

I have something that I’m hoping to get up soon, and hopefully in the future there will be less time between posts!

mark

By: Henry Dominik

Henry Dominik — Tue, 23 Feb 2010 13:44:20 +0000

He seems to have resumed blogging again. Check out the post he made in January of this year. I’m happy he’s back

By: PC Repair

PC Repair — Sun, 29 Nov 2009 17:14:26 +0000

Just wondering why we have not seen you in a long time.
I personally have missed your amazing step-by-step tutorial.

We hope you’re fine and wish you the very best.
Good luck

By: Cillia johnson

Cillia johnson — Sun, 29 Nov 2009 17:11:25 +0000

This is great. I was having difficulties because of spaces in my indentation, but that has now been solved. It took me days to figure the indentation problem out as a beginner

Nice tutorial BTW ..

By: SoftwareExplorer

SoftwareExplorer — Thu, 19 Nov 2009 23:19:26 +0000

You said “handled so *wall*” instead of “handled so *well*”. Ted mentioned this, but he was talking about a few other errors two, so you probably didn’t notice the change.

Thanks for these tutorials. They are the best I have found so far.

By: ksamuel

ksamuel — Wed, 07 Oct 2009 10:29:38 +0000

Makes me think of this tuto :

http://stackoverflow.com/questions/231767#answer-231855

By: Rune

Rune — Mon, 13 Jul 2009 12:06:55 +0000

Very informative and well written article!