How does Python 2.7.3 hash strings used to seed random number generators?

Question

In 64 bit Python 2.7.6 this is True, however in 32 bit Python 2.7.3 it is False:

random.Random(hash("a")).random() == random.Random("a").random()

So how does Python 2.7.3 hash strings used to seed random number generators?

Answer 1

it's because on 32bit hash("a") is a negative number (because of platform long type size) and the random modules behaves differently.

The random module seed() function:

• passing int or long it will use PyNumber_Absolute() that is abs()
• passing an object (a string) it will use PyLong_FromUnsignedLong((unsigned long)hash)

sign bit truncation and abs give different result

e.g.:

• abs(-10) = 10
• ((unsigned long) -10) = 4294967286