[14:54] home:~ echo "line1
> line2
> <begin>
> line4
> line5
> <end>" > file
[14:54] home:~ bpython
>>> lines = map(lambda s: s.strip(), open('file', 'r').readlines())
>>> print '\n'.join(lines[lines.index('<begin>')+1:lines.index('<end>')])
line4
line5

>>> with open('file', 'r') as f:
...     while f.next().strip() != '<begin>':
...         pass
...     for line in f:
...         if line.strip() == '<end>':
...             break
...         else:
...             print line.strip()
...             
line4
line5