This ensures that the random password has one upper, one lower, one number, one special character and is longer than 8 characters. This should cover any complexity requirement. In your model, create a cla-- that inherits from Auth then simply override the random_password function:

from gluon.tools import *
class MyAuth(Auth):    
    def random_password(self):
        import string
        import random
        password = ''
        specials=r'!#$*?'         
        for i in range(0,3):
            password += random.choice(string.lowercase)
            password += random.choice(string.uppercase)
            password += random.choice(string.digits)
            password += random.choice(specials)            
        return ''.join(random.sample(password,len(password)))

auth=MyAuth(globals(),db)

Depricated