def rand_alnum(length=0):
 jibber = ''.join([letters, digits])
 return ''.join((choice(jibber) for _ in xrange((length or randint(10, 30)))))

def rand_alnum ( length = 0 ) : jibber = '' . join ( [ letters , digits ] ) return '' . join ( ( choice ( jibber ) for _ in xrange ( ( length or randint ( 10 , 30 ) ) ) ) )
create a random string with random length :return: a random string of with length > 10 and length < 30 .