[Python-Dev] os.urandom API (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Sun Aug 29 23:26:20 CEST 2004

Raymond Hettinger wrote:

I would like to change the API for the new os.urandom(n) function to return a long integer instead of a string. The former better serves more use cases and fits better with existing modules.

-1. Bytes is what the underlying system returns, and it is also conceptually the right thing. We are really talking about a stream of random bytes here (where u signals unlimitedness).

1) The call random.seed(os.random(100)) is a likely use case. If the intermediate value is a string, then random.seed() will hash it and only use 32 bits. If the intermediate value is a long integer, all bits are used. In the given example, the latter is clearly what the user expects (otherwise, they would only request 4 bytes).

Then add an os.randint if you think this is important. Given the easiness of using the struct module, I don't think it is important to provide this out of the box.

2) Another likely use case is accessing all the tools in the random module with a subclass that overrides random() and getrandbits(). Both can be done easier and faster if os.random() returns long integers. If the starting point is a string, the code gets ugly and slow.

Don't try guessing use cases too much. I don't think either the original submitter, nor the original reviewer, had sequences of pseudo-random numbers as their use case. Instead, the typical application will be a one-time token for some crypto algorithm, in which case sequences of pseudo-randomness are evil. What kind of data structure these things will need is hard to guess, but "sequence of bytes" is a good bet.

3) Most use cases for random values involve numeric manipulation. Simple tasks like finding a random integer in the range [0,100000) become unnecessarily more complicated when starting from a string.

That is not true. Most use cases of random numbers involve bit manipulation.

1) This form is handy for cyptoweenies to xor with other byte strings (perhaps for a one-time pad).

And indeed, cryptoweenies have contributed that code. He who writes the code choses the interface.

Regards, Martin

More information about the Python-Dev mailing list