iterator? way of generating all possible combinations?

Scott David Daniels scott.daniels at acm.org
Wed May 31 18:45:10 CEST 2006


Jim Segrave wrote:
> In article <447cadf6$1 at nntp0.pdx.net>,
> Scott David Daniels  <scott.daniels at acm.org> wrote:
>>     class FileReIterable2(object):
>>         ...
>>         def __iter__(self):
>>             self.file.seek(0)
>>             for line in self.file:
>>                 nextpos = self.file.tell()
>>                 yield line
>>                 self.file.seek(nextpos)
> 
> Hmm - I tried this with 'one.file' being ... letters, one per line:
> 
> gen = FileReIterable2("one.file")
> for a in gen:
>   for b in gen:
>     print a.strip(), b.strip()
> 
> which didn't produce lines 'a a', 'a b', etc. It produced the single
> line 'a a', then stopped....
Oops.  This works in Python 2.5 (and later) because the file.tell and
file.seek code are aware of the file iteration buffering.  Since I am
trying to test all of my stuff on 2.5, that is what I am using by
default.

> Rewriting the __iter__ method to not internally iterate over the file
> object, as follows, works ....
> 
> class FileReIterable2(object):
>     ...
>     def __iter__(self):
>         self.file.seek(0)
>         while True:
>             line = self.file.readline()
>             if line == '': raise StopIteration
>             nextpos = self.file.tell()
>             yield line
>             self.file.seek(nextpos)

This fix does in fact provide working behavior for Pythons before 2.5.

--Scott David Daniels
scott.daniels at acm.org



More information about the Python-list mailing list