Python Regex Question

[MalteseUnderdog]

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.

My idea (primitive) ^start.*?x=Dog doesn't work because clearly it
would return results

start
x=Dog  # (good)

and

start
x=Cat
stop
start
x=Dog # bad since I only want start ... x=Dog portion

Can you help me ?

Thanks
JP, Malta.