Class PRF

Create a PRF keyed with the given key and max.

The key must be a string whereas the max must be a number. Output value will be in the range zero to max, with zero included and max excluded.

To make a PRF what generates numbers less than 1000 do:

>>> f = PRF("key", 1000)

The PRF can be evaluated by calling it on some input:

>>> f("input")
327L

Creating another PRF with the same key gives identical results since f and g are deterministic functions, depending only on the key:

>>> g = PRF("key", 1000)
>>> g("input")
327L

We can test that f and g behave the same on many inputs:

>>> [f(i) for i in range(100)] == [g(i) for i in range(100)]
True

Both the key and the max is used when the PRF is keyed. This means that

>>> f = PRF("key", 1000)
>>> g = PRF("key", 10000)
>>> [f(i) for i in range(100)] == [g(i) for i in range(100)]
False

Overrides: object.__init__

Return a number based on input.

If the input is not already a string, it is hashed (using the normal Python hash built-in) and the hash value is used instead. The hash value is a 32 bit value, so a string should be given if one wants to evaluate the PRF on more that 2**32 different values.

>>> prf = PRF("key", 1000)
>>> prf(1), prf(2), prf(3)
(501L, 432L, 133L)

Since prf is a function we can of course evaluate the same input to get the same output:

>>> prf(1)
501L

The prf can take arbitrary input:

>>> prf(("input", 123))
284L

Non-string input will be converted with str, which means that the input must have a deterministic __str__ method. This means that hashable instances are probably best.