I have python 2.7 and am trying to issue:

glob('{faint,bright*}/{science,calib}/chip?/')

I obtain no matches, however from the shell echo {faint,bright*}/{science,calib}/chip? gives:

faint/science/chip1 faint/science/chip2 faint/calib/chip1 faint/calib/chip2 bright1/science/chip1 bright1/science/chip2 bright1w/science/chip1 bright1w/science/chip2 bright2/science/chip1 bright2/science/chip2 bright2w/science/chip1 bright2w/science/chip2 bright1/calib/chip1 bright1/calib/chip2 bright1w/calib/chip1 bright1w/calib/chip2 bright2/calib/chip1 bright2/calib/chip2 bright2w/calib/chip1 bright2w/calib/chip2

What is wrong with my expression?

Since {} aren't supported by glob() in Python, what you probably want is something like

import os
import re

...

match_dir = re.compile('(faint|bright.*)/(science|calib)(/chip)?')
for dirpath, dirnames, filenames in os.walk("/your/top/dir")
    if match_dir.search(dirpath):
        do_whatever_with_files(dirpath, files)
        # OR
        do_whatever_with_subdirs(dirpath, dirnames)