How does python's random.Random.seed work?

Question

I'm used to typing random.randrange. I'll do a from random import Random to spot the error from now on.

For a game involving procedural generation (nope, not a Minecraft clone :p) I'd like to keep several distinct pseudo-random number generators:

one for the generation of the world (landscape, quests, etc.),
one for the random events that can happen in the world (such as damage during fight).

The rationale being that I want to be able to reproduce the first, so I don't want the second one to interfere.

I thought random.Random was made for that. However something is puzzling me:

import random
rnd = random.Random()
rnd.seed(0)
print [random.randrange(5) for i in range(10)]
rnd.seed(0)
print [random.randrange(5) for i in range(10)]

produces two different sequences. When I do rnd = random then things work as expected, but I do need several generators.

What am I missing?

It actually took me a few minutes to spot that too. Don't feel bad happens to all of us, glad it's solved :) — Rob Wouters
– Rob Wouters, Commented Jan 25, 2012 at 21:00

Johan Lundberg · Accepted Answer · 2016-05-05 15:13:09Z

13

It works almost exactly as you tried but the rnd.seed() applies to the rnd object

just use

rnd = random.Random(0) # <<-- or set it here 
rnd.seed(7)
print [rnd.randrange(5) for i in range(10)]

or by setting the global seed, like this:

random.seed(7)
print [random.randrange(5) for i in range(10)]

edited May 5, 2016 at 15:13

answered Jan 25, 2012 at 20:14

Johan Lundberg

27.3k13 gold badges76 silver badges101 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Rob Wouters · Accepted Answer · 2012-01-25 20:17:55Z

4

Pass the seed to the constructor of Random:

>>> import random
>>> rnd = random.Random(0)
>>> [rnd.randint(0, 10) for i in range(10)]
[9, 8, 4, 2, 5, 4, 8, 3, 5, 6]
>>> rnd = random.Random(0)
>>> [rnd.randint(0, 10) for i in range(10)]
[9, 8, 4, 2, 5, 4, 8, 3, 5, 6]
>>> rnd = random.Random(1)
>>> [rnd.randint(0, 10) for i in range(10)]
[1, 9, 8, 2, 5, 4, 7, 8, 1, 0]

answered Jan 25, 2012 at 20:17

Rob Wouters

16.4k3 gold badges44 silver badges36 bronze badges

Collectives™ on Stack Overflow

How does python's random.Random.seed work?

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related