suitable_regex

import re

RE_PATTERNS = re.compile(r"(?:Issue ?)?#?(\d+)", flags=re.MULTILINE | re.IGNORECASE)


test_messages = [
    """#123""",
    """Issue #123""",
    """Issue#123""",
    """Issue123""",
    """Issue 123""",
    """Multiline
    #1234
    Issue1134""",
    """Multiline
    Issue1234,
    #12345,
    Issue 12345"""
]


for message in test_messages:
    print RE_PATTERNS.sub(r"bpo-\1", message)