Python Regex Question

[Terry Reedy]

MalteseUnderdog wrote:
> Hi there I just started python (but this question isn't that trivial
> since I couldn't find it in google :) )
> 
> I have the following text file entries (simplified)
> 
> start      #frag 1 start
> x=Dog # frag 1 end
> stop
> start    # frag 2 start
> x=Cat # frag 2 end
> stop
> start     #frag 3 start
> x=Dog #frag 3 end
> stop
> ....
> 
> I need a regex expression which returns the start to the x=ANIMAL for
> only the x=Dog fragments so all my entries should be start ...
> (something here) ... x=Dog .  So I am really interested in fragments 1
> and 3 only.

As I understand the above....
I would first write a generator that separates the file into fragments 
and yields them one at a time.  Perhaps something like

def fragments(ifile):
   frag = []
   for line in ifile:
     frag += line
     if <line ends fragment>:
       yield frag
       frag = []

Then I would iterate through fragments, testing for the ones I want:

for frag in fragments(somefile):
   if 'x=Dog' in frag:
     <do whatever>

Terry Jan Reedy