In article <mailman.372.1427809109.10327.python-l...@python.org>,
Dave Angel <da...@davea.name> wrote:
>On 03/31/2015 09:18 AM, Albert van der Horst wrote:
>> In article <55062bda$0$12998$c3e8da3$54964...@news.astraweb.com>,
>> Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote:
>
>>>
>>> The biggest difference is syntactic. Here's an iterator which returns a
>>> never-ending sequence of squared numbers 1, 4, 9, 16, ...
>>>
>>> class Squares:
>>> def __init__(self):
>>> self.i = 0
>>> def __next__(self):
>>> self.i += 1
>>> return self.i**2
>>> def __iter__(self):
>>> return self
>>
>> You should give an example of usage. As a newby I'm not up to
>> figuring out the specification from source for
>> something built of the mysterious __ internal
>> thingies.
>> (I did experiment with Squares interactively. But I didn't get
>> further than creating a Squares object.)
>>
>
>He did say it was an iterator. So for a first try, write a for loop:
>
>class Squares:
> def __init__(self):
> self.i = 0
> def __next__(self):
> self.i += 1
> return self.i**2
> def __iter__(self):
> return self
>
>for i in Squares():
> print(i)
> if i > 50:
> break
>
This is what I get:
/ --------------------------
albert@cherry:/tmp$ more aap.py
class Squares:
def __init__(self):
self.i = 0
def __next__(self):
self.i += 1
return self.i**2
def __iter__(self):
return self
albert@cherry:/tmp$ python
Python 2.6.6 (r266:84292, Dec 26 2010, 22:31:48)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from aap import *
>>> for i in Squares():
... print i
... if i>50: break
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: instance has no next() method
>>>
/ --------------------------
Probably not what is intended.
Last minute note:
renaming __next__() into next() did the job.
>--
>DaveA
Groetjes Albert
--
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst
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