1# test re.sub with unmatched groups, behaviour changed in CPython 3.5
2
3try:
4    import ure as re
5except ImportError:
6    try:
7        import re
8    except ImportError:
9        print("SKIP")
10        raise SystemExit
11
12try:
13    re.sub
14except AttributeError:
15    print("SKIP")
16    raise SystemExit
17
18# first group matches, second optional group doesn't so is replaced with a blank
19print(re.sub(r"(a)(b)?", r"\2-\1", "1a2"))
20