Neaten-up random module docs.

This commit is contained in:
Raymond Hettinger 2010-12-02 05:35:35 +00:00
parent b2ddf7979d
commit 3cdf871a8c
1 changed files with 31 additions and 30 deletions

View File

@ -233,41 +233,18 @@ be found in any statistics text.
parameter.
Alternative Generators:
Alternative Generator:
.. class:: SystemRandom([seed])
Class that uses the :func:`os.urandom` function for generating random numbers
from sources provided by the operating system. Not available on all systems.
Does not rely on software state and sequences are not reproducible. Accordingly,
Does not rely on software state, and sequences are not reproducible. Accordingly,
the :meth:`seed` method has no effect and is ignored.
The :meth:`getstate` and :meth:`setstate` methods raise
:exc:`NotImplementedError` if called.
Examples of basic usage::
>>> random.random() # Random float x, 0.0 <= x < 1.0
0.37444887175646646
>>> random.uniform(1, 10) # Random float x, 1.0 <= x < 10.0
1.1800146073117523
>>> random.randint(1, 10) # Integer from 1 to 10, endpoints included
7
>>> random.randrange(0, 101, 2) # Even integer from 0 to 100
26
>>> random.choice('abcdefghij') # Choose a random element
'c'
>>> items = [1, 2, 3, 4, 5, 6, 7]
>>> random.shuffle(items)
>>> items
[7, 3, 2, 5, 6, 4, 1]
>>> random.sample([1, 2, 3, 4, 5], 3) # Choose 3 elements
[4, 1, 5]
.. seealso::
M. Matsumoto and T. Nishimura, "Mersenne Twister: A 623-dimensionally
@ -280,6 +257,7 @@ Examples of basic usage::
random number generator with a long period and comparatively simple update
operations.
Notes on Reproducibility
========================
@ -297,11 +275,34 @@ change across Python versions, but two aspects are guaranteed not to change:
sequence when the compatible seeder is given the same seed.
.. _random-examples:
Examples and Recipes
====================
Basic usage::
>>> random.random() # Random float x, 0.0 <= x < 1.0
0.37444887175646646
>>> random.uniform(1, 10) # Random float x, 1.0 <= x < 10.0
1.1800146073117523
>>> random.randrange(10) # Integer from 0 to 9
7
>>> random.randrange(0, 101, 2) # Even integer from 0 to 100
26
>>> random.choice('abcdefghij') # Single random element
'c'
>>> items = [1, 2, 3, 4, 5, 6, 7]
>>> random.shuffle(items)
>>> items
[7, 3, 2, 5, 6, 4, 1]
>>> random.sample([1, 2, 3, 4, 5], 3) # Three samples without replacement
[4, 1, 5]
A common task is to make a :func:`random.choice` with weighted probababilites.
If the weights are small integer ratios, a simple technique is to build a sample
@ -312,9 +313,9 @@ population with repeats::
>>> random.choice(population)
'Green'
A more general approach is to arrange the weights in a cumulative probability
distribution with :func:`itertools.accumulate`, and then locate the random value
with :func:`bisect.bisect`::
A more general approach is to arrange the weights in a cumulative distribution
with :func:`itertools.accumulate`, and then locate the random value with
:func:`bisect.bisect`::
>>> choices, weights = zip(*weighted_choices)
>>> cumdist = list(itertools.accumulate(weights))