Question

The below code attempts to illustrate what I want. I basically want two instances of “random” that operate independently of each other. I want to seed “random” within one class without affecting “random” in another class. How can I do that?

class RandomSeeded:
    def __init__(self, seed):
        import random as r1
        self.random = r1
        self.random.seed(seed)
    def get(self):
        print self.random.choice([4,5,6,7,8,9,2,3,4,5,6,7,])

class Random:
    def __init__(self):
        import random as r2
        self.random = r2
        self.random.seed()
    def get(self): 
        print self.random.choice([4,5,6,7,8,9,2,3,4,5,6,7,])

if __name__ == '__main__':
    t = RandomSeeded('asdf')
    t.get()       # random is seeded within t
    s = Random()
    s.get()       
    t.get()       # random should still be seeded within t, but is no longer

Answer 1

Class random.Random exists specifically to allow the behavior you want — modules are intrinsically singletons, but classes are meant to be multiply instantiated, so both kinds of needs are covered.

Should you ever need an independent copy of a module (which you definitely don’t in the case of random!), try using copy.deepcopy on it — in many cases it will work. However, the need is very rare, because modules don’t normally keep global mutable states except by keeping one privileged instance of a class they also offer for “outside consumption” (other examples besided random include fileinput).