Can't generate different random numbers in Python

Question

I'm having this problem in python where I can't generate different random numbers in a loop. Every loop generates same numbers. My code looks like this:

import random

class Dna :
    genes = []

    def __init__(self, lifespan) :

        sum = 0
        for i in range(lifespan) :
            self.genes.append(PVector(random.randrange(-10, 10), random.randrange(-10, 10)))
            sum += self.genes[i].mag()

        print(sum)

Here, I'm trying to generate random vectors in the range -10 and 10 but every different DNA object prints the same sum. Here is the main file:

import dna

def setup() :

    d = dna.Dna(200)
    d2 = dna.Dna(200)

And I'm using processing.py for this.

You're missing some vitally important code in your question. — cs95
– cs95, Commented Feb 28, 2018 at 10:53
Which one? If you're talking about that 'population' line, you can ignore that — Se7eN
– Se7eN, Commented Feb 28, 2018 at 10:55
@MosteM Thanks for the suggestion but I don't need to generate same streams of random numbers. — Se7eN
– Se7eN, Commented Feb 28, 2018 at 11:02
@ibt23sec5 It's processing's built-in object for 2D and 3D Vectors — Se7eN
– Se7eN, Commented Feb 28, 2018 at 11:02
If you want to diagnose such things in future, try doing print(self.genes) at the start and end of the constructor, and watch it grow. — user9423368
– user9423368, Commented Feb 28, 2018 at 11:12

user9423368 · Accepted Answer · 2018-02-28 10:57:42Z

6

genes needs to be an instance variable (one copy per instance of Dna class), not a class variable (one copy for the Dna class, shared by all instances).

def __init__(self, lifespan):
    self.genes = []

answered Feb 28, 2018 at 10:57

user9423368

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1 Comment

Se7eN Over a year ago

Oh thanks man. I guess I'm missing some knowledge about classes in Python. :)

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