Question

I am converting some c code to python. I am wondering that is there any drand48() equivalent in python(exactly the same!) or a wrapper to it?

Thanks a lot

Answer 1

You are looking for random.random.

>>> import random
>>> help(random)
>>> random.random()
0.8423026866867628

It does not use the same generator as drand48. The drand48 family uses a 48-bit linear congruential generator, whereas the Python random module uses the superior Mersenne Twister algorithm.

If you want the exact same output as drand48, you can implement it in Python.

# Uncomment the next line if using Python 2.x...
# from __future__ import division
class Rand48(object):
    def __init__(self, seed):
        self.n = seed
    def seed(self, seed):
        self.n = seed
    def srand(self, seed):
        self.n = (seed << 16) + 0x330e
    def next(self):
        self.n = (25214903917 * self.n + 11) & (2**48 - 1)
        return self.n
    def drand(self):
        return self.next() / 2**48
    def lrand(self):
        return self.next() >> 17
    def mrand(self):
        n = self.next() >> 16
        if n & (1 << 31):
            n -= 1 << 32
        return n   

However, the output will be significantly inferior to Python’s standard random number generator. The rand48 family of functions were declared obsolete in 1989 by SVID 3.