help with simple script and strings

[seth vidal]

On Sat, 2008-04-12 at 13:35 -0700, John Poelstra wrote:
> I'm just getting started with python.  Curious what I need to change to 
> properly filter out only strings starting with "200"
> 
> script:
> #!/usr/bin/python
> 
> directories = ['20080412', '20080324', 'blahblah', 'latest-dir', 
> 'rawhide-20080410', 'rawhide-20080411', 'rawhide-20080412' , '20080401']
> 
> print 'directories == %s' % directories
> 
> for directory in directories:
>      print 'processing directory %s ' % directory
>      if not directory.startswith('200'):
>          directories.remove(directory)
>          print 'removed == %s' % directory
> 
> print 'directories == %s' % directories
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~
> output:
> $ python dir-filter.py
> directories == ['20080412', '20080324', 'blahblah', 'latest-dir', 
> 'rawhide-20080410', 'rawhide-20080411', 'rawhide-20080412', '20080401']
> processing directory 20080412
> type == <type 'str'>
> processing directory 20080324
> type == <type 'str'>
> processing directory blahblah
> type == <type 'str'>
> removed == blahblah
> processing directory rawhide-20080410
> type == <type 'str'>
> removed == rawhide-20080410
> processing directory rawhide-20080412
> type == <type 'str'>
> removed == rawhide-20080412
> directories == ['20080412', '20080324', 'latest-dir', 
> 'rawhide-20080411', '20080401']
> 
> ~~~~~~~~~~~~~~~~~~~~
> 
> why do 'rawhide-20080411' and 'latest-dir' remain?

removing items from a list you're working on means the index change in
place

so you'll end up skipping some items b/c the loop moves over them.

-sv