How to overide "for line in file:"

[Harry George]

Shalabh Chaturvedi <shalabh at cafepy.com> writes:

> David Morgenthaler wrote:
> 
> > How does one overide the iterator implied by the construct "for line
> > in file:"?
> > 
> 
> 'for' uses __iter__().
> 
> Subclass file and redefine __iter__(self). It should return an object that
> has the next() method which returns the next item, or raises StopIteration
> if finished. Returning self from __iter__() is ok (then you can put the
> next() in the same class). 
> 
> An easier alternative is to make __iter__() a generator function (so calling
> it automatically returns a 'generator' object, which has next() on it, and
> also raises StopIteration when done).
> 
> HTH,
> Shalabh


Slightly off topic, how do you "reset" or backup an iter?  Someone
asked me a couple of days ago how to use yield and then backup if the
yielded line failed to meet certain criteria.  Essentailly a
lookahead(1) situation.

Historically, I've made a list, kept track of the line index, and
decremented that when I needed to backup.  Does iter have something
equiv?


-- 
harry.g.george at boeing.com
6-6M21 BCA CompArch Design Engineering
Phone: (425) 342-0007