Braced shell expansion

bracedexpand.py

import itertools
import re
import sys

try:
    INPUT = sys.argv[1]
except:
    print('Usage: {} <string-to-expand>'.format(sys.argv[0]), file=sys.stderr)
    sys.exit(1)

def intersperse(l1, l2):
    assert len(list(l1)) == len(list(l2)), "naive implementation"
    for x1, x2 in zip(l1, l2):
        yield x1
        yield x2

# Check out the docs for how re.split handles parenthesized captures.
l = re.split(r'\{([^\}]*)\}', INPUT)
chunks, braceds = l[::2], l[1::2]
braceds = [x.split(',') for x in braceds]
# re.split always has 1 more "in between" piece (chunks)
# than match piece (braceds), so add a dummy entry at the end of braceds
# to make them the same length.
# This makes the code for "interspersing" the entries easier.
braceds.append([''])

for prod in itertools.product(*braceds):
    print(''.join(intersperse(chunks, prod)))

TODO: handle recursive expansion e.g. --foo{bar{baz,qux},quux}