Grab and Parse a chunkc of text

[Gribouillis]

I propose the use of a general function to grab a group of items from a sequence between the first item that satisfies a predicate to the first item that satisfies another predicate. You can easily write a small library for this

from pathlib import Path
import re

class EmptyGroup(RuntimeError):
    pass

def grab(seq, start, stop):
    """Grabs items in a sequence starting with the first
    item for which the predicate start(item) is True until
    the first item if any for which the predicate stop(item)
    is True.
    
    If no item is grabbed, raise the EmptyGroup exception.
    """
    seq = iter(seq)
    for x in seq:
        if start(x):
            yield x
            break
    else:
        raise EmptyGroup
    for x in seq:
        yield x
        if stop(x):
            return

def all_grabbed(seq, start, stop):
    """Generate items extracted from a sequence by calling
    repetively grab(seq, start, stop) until an empty group
    is returned.
    """
    seq = iter(seq)
    try:
        while True:
            yield from grab(seq, start, stop)
    except EmptyGroup:
        pass

def main():
    start = re.compile(r'^Switch').search
    stop = re.compile(r'^$').search
    with Path('paillasse/tmpswitch.log').open() as ifh:
        for x in all_grabbed(ifh, start, stop):
            print(repr(x))

if __name__ == '__main__':
    main()

Here is the contents of paillasse/tmpswitch.log

Output:
Stack# show version

Switch Ports Model SW Version SW Image
------ ----- ----- ---------- ----------
* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M
2 28 WS-C3750E-24PS 12.2(46)SE C3750E-UNIVERSAL-M
3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSAL-M

foo bar baz

Switch Ports Model SW Version SW Image
------ ----- ----- ---------- ----------
* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M
2 28 WS-C3750E-24PS 12.2(46)SE C3750E-UNIVERSAL-M
3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSAL-M

nooo

and here is the program's output

Output:
'Switch Ports Model SW Version SW Image\n'
'------ ----- ----- ---------- ----------\n'
'* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M\n'
'2 28 WS-C3750E-24PS 12.2(46)SE C3750E-UNIVERSAL-M\n'
'3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSAL-M\n'
'\n'
'Switch Ports Model SW Version SW Image\n'
'------ ----- ----- ---------- ----------\n'
'* 1 30 WS-C3750E-24PD 12.2(46)SE C3750E-UNIVERSAL-M\n'
'2 28 WS-C3750E-24PS 12.2(46)SE C3750E-UNIVERSAL-M\n'
'3 54 WS-C3750E-48TD 12.2(46)SE C3750E-UNIVERSAL-M\n'
'\n'