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Remove defunct parts of the random module

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Raymond Hettinger 2008-01-13 23:40:30 +00:00
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Doc/library/random.rst
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@ -28,25 +28,14 @@ for cryptographic purposes.
The functions supplied by this module are actually bound methods of a hidden
instance of the :class:`random.Random` class. You can instantiate your own
instances of :class:`Random` to get generators that don't share state. This is
especially useful for multi-threaded programs, creating a different instance of
:class:`Random` for each thread, and using the :meth:`jumpahead` method to make
it likely that the generated sequences seen by each thread don't overlap.
instances of :class:`Random` to get generators that don't share state.
Class :class:`Random` can also be subclassed if you want to use a different
basic generator of your own devising: in that case, override the :meth:`random`,
:meth:`seed`, :meth:`getstate`, :meth:`setstate` and :meth:`jumpahead` methods.
:meth:`seed`, :meth:`getstate`, and :meth:`setstate`.
Optionally, a new generator can supply a :meth:`getrandombits` method --- this
allows :meth:`randrange` to produce selections over an arbitrarily large range.
As an example of subclassing, the :mod:`random` module provides the
:class:`WichmannHill` class that implements an alternative generator in pure
Python. The class provides a backward compatible way to reproduce results from
earlier versions of Python, which used the Wichmann-Hill algorithm as the core
generator. Note that this Wichmann-Hill generator can no longer be recommended:
its period is too short by contemporary standards, and the sequence generated is
known to fail some stringent randomness tests. See the references below for a
recent variant that repairs these flaws.
Bookkeeping functions:
@ -79,17 +68,6 @@ Bookkeeping functions:
the time :func:`setstate` was called.
.. function:: jumpahead(n)
Change the internal state to one different from and likely far away from the
current state. *n* is a non-negative integer which is used to scramble the
current state vector. This is most useful in multi-threaded programs, in
conjuction with multiple instances of the :class:`Random` class:
:meth:`setstate` or :meth:`seed` can be used to force all instances into the
same internal state, and then :meth:`jumpahead` can be used to force the
instances' states far apart.
.. function:: getrandbits(k)
Returns a python integer with *k* random bits. This method is supplied with
@ -224,24 +202,6 @@ be found in any statistics text.
Alternative Generators:
.. class:: WichmannHill([seed])
Class that implements the Wichmann-Hill algorithm as the core generator. Has all
of the same methods as :class:`Random` plus the :meth:`whseed` method described
below. Because this class is implemented in pure Python, it is not threadsafe
and may require locks between calls. The period of the generator is
6,953,607,871,644 which is small enough to require care that two independent
random sequences do not overlap.
.. function:: whseed([x])
This is obsolete, supplied for bit-level compatibility with versions of Python
prior to 2.1. See :func:`seed` for details. :func:`whseed` does not guarantee
that distinct integer arguments yield distinct internal states, and can yield no
more than about 2\*\*24 distinct internal states in all.
.. class:: SystemRandom([seed])
Class that uses the :func:`os.urandom` function for generating random numbers
@ -281,6 +241,4 @@ Examples of basic usage::
equidistributed uniform pseudorandom number generator", ACM Transactions on
Modeling and Computer Simulation Vol. 8, No. 1, January pp.3-30 1998.
Wichmann, B. A. & Hill, I. D., "Algorithm AS 183: An efficient and portable
pseudo-random number generator", Applied Statistics 31 (1982) 188-190.