Iterate over text file, discarding some lines via context manager

Dave Angel davea at
Fri Nov 28 16:22:18 CET 2014

On 11/28/2014 10:04 AM, fetchinson . wrote:
> Hi all,
> I have a feeling that I should solve this by a context manager but
> since I've never used them I'm not sure what the optimal (in the
> python sense) solution is. So basically what I do all the time is
> this:
> for line in open( 'myfile' ):
>      if not line:
>          # discard empty lines
>          continue
>      if line.startswith( '#' ):
>          # discard lines starting with #
>          continue
>      items = line.split( )
>      if not items:
>          # discard lines with only spaces, tabs, etc
>          continue
>      process( items )
> You see I'd like to ignore lines which are empty, start with a #, or
> are only white space. How would I write a context manager so that the
> above simply becomes
> with some_tricky_stuff( 'myfile' ) as items:
>      process( items )

I see what you're getting at, but a context manager is the wrong 
paradigm.  What you want is a generator.   (untested)

def mygenerator(filename):
     with open(filename) as f:
         for line in f:
             if not line: continue
             if line.startswith('#'): continue
             items = line.split()
             if not items: continue
             yield items

Now your caller simply does:

for items in mygenerator(filename):


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