def choose(a, choices, mode='raise'):
'''Return dataset with items drawn from choices according to conditions'''
if mode == 'raise':
rf = True
cf = False
else:
rf = False
if mode == 'clip':
cf = True
elif mode == 'wrap':
cf = False
else:
raise ValueError, "mode is not one of raise, clip or wrap"
return _dsutils.choose(a, choices, rf, cf)
