import re
some_regex = re.compile("^foo(?P<idx>[0-9]*)?$")
match = some_regex.match('foo11')
print(match and 'idx' in match.groupdict())
match = some_regex.match('bar11')
print(match and 'idx' in match.groupdict())
aW1wb3J0IHJlCnNvbWVfcmVnZXggPSByZS5jb21waWxlKCJeZm9vKD9QPGlkeD5bMC05XSopPyQiKQoKbWF0Y2ggPSBzb21lX3JlZ2V4Lm1hdGNoKCdmb28xMScpCnByaW50KG1hdGNoIGFuZCAnaWR4JyBpbiBtYXRjaC5ncm91cGRpY3QoKSkKCm1hdGNoID0gc29tZV9yZWdleC5tYXRjaCgnYmFyMTEnKQpwcmludChtYXRjaCBhbmQgJ2lkeCcgaW4gbWF0Y2guZ3JvdXBkaWN0KCkp