def get_challenge():
 global challenge
 challenge = ''.join((random.SystemRandom().choice((string.ascii_uppercase + string.digits)) for _ in range(256)))
 return '{}'.format(challenge)

def get_challenge ( ) : global challenge challenge = '' . join ( ( random . SystemRandom ( ) . choice ( ( string . ascii_uppercase + string . digits ) ) for _ in range ( 256 ) ) ) return '{}' . format ( challenge )
return an ascii challenge to validate authentication in _check_challenge .