2007-08-15 11:28:01 -03:00
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:mod:`random` --- Generate pseudo-random numbers
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================================================
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.. module:: random
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:synopsis: Generate pseudo-random numbers with various common distributions.
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This module implements pseudo-random number generators for various
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distributions.
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For integers, uniform selection from a range. For sequences, uniform selection
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of a random element, a function to generate a random permutation of a list
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in-place, and a function for random sampling without replacement.
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On the real line, there are functions to compute uniform, normal (Gaussian),
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lognormal, negative exponential, gamma, and beta distributions. For generating
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distributions of angles, the von Mises distribution is available.
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Almost all module functions depend on the basic function :func:`random`, which
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generates a random float uniformly in the semi-open range [0.0, 1.0). Python
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uses the Mersenne Twister as the core generator. It produces 53-bit precision
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floats and has a period of 2\*\*19937-1. The underlying implementation in C is
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both fast and threadsafe. The Mersenne Twister is one of the most extensively
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tested random number generators in existence. However, being completely
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deterministic, it is not suitable for all purposes, and is completely unsuitable
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for cryptographic purposes.
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The functions supplied by this module are actually bound methods of a hidden
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instance of the :class:`random.Random` class. You can instantiate your own
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instances of :class:`Random` to get generators that don't share state. This is
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especially useful for multi-threaded programs, creating a different instance of
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:class:`Random` for each thread, and using the :meth:`jumpahead` method to make
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it likely that the generated sequences seen by each thread don't overlap.
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Class :class:`Random` can also be subclassed if you want to use a different
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basic generator of your own devising: in that case, override the :meth:`random`,
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:meth:`seed`, :meth:`getstate`, :meth:`setstate` and :meth:`jumpahead` methods.
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Optionally, a new generator can supply a :meth:`getrandbits` method --- this
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allows :meth:`randrange` to produce selections over an arbitrarily large range.
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.. versionadded:: 2.4
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the :meth:`getrandbits` method.
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As an example of subclassing, the :mod:`random` module provides the
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:class:`WichmannHill` class that implements an alternative generator in pure
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Python. The class provides a backward compatible way to reproduce results from
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earlier versions of Python, which used the Wichmann-Hill algorithm as the core
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generator. Note that this Wichmann-Hill generator can no longer be recommended:
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its period is too short by contemporary standards, and the sequence generated is
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known to fail some stringent randomness tests. See the references below for a
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recent variant that repairs these flaws.
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.. versionchanged:: 2.3
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Substituted MersenneTwister for Wichmann-Hill.
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Bookkeeping functions:
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.. function:: seed([x])
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Initialize the basic random number generator. Optional argument *x* can be any
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:term:`hashable` object. If *x* is omitted or ``None``, current system time is used;
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current system time is also used to initialize the generator when the module is
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first imported. If randomness sources are provided by the operating system,
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they are used instead of the system time (see the :func:`os.urandom` function
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for details on availability).
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.. versionchanged:: 2.4
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formerly, operating system resources were not used.
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If *x* is not ``None`` or an int or long, ``hash(x)`` is used instead. If *x* is
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an int or long, *x* is used directly.
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.. function:: getstate()
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Return an object capturing the current internal state of the generator. This
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object can be passed to :func:`setstate` to restore the state.
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.. versionadded:: 2.1
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2007-12-03 15:20:02 -04:00
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.. versionchanged:: 2.6
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State values produced in Python 2.6 cannot be loaded into earlier versions.
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2007-08-15 11:28:01 -03:00
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.. function:: setstate(state)
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*state* should have been obtained from a previous call to :func:`getstate`, and
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:func:`setstate` restores the internal state of the generator to what it was at
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the time :func:`setstate` was called.
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.. versionadded:: 2.1
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.. function:: jumpahead(n)
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Change the internal state to one different from and likely far away from the
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current state. *n* is a non-negative integer which is used to scramble the
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current state vector. This is most useful in multi-threaded programs, in
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conjunction with multiple instances of the :class:`Random` class:
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:meth:`setstate` or :meth:`seed` can be used to force all instances into the
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same internal state, and then :meth:`jumpahead` can be used to force the
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instances' states far apart.
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.. versionadded:: 2.1
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.. versionchanged:: 2.3
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Instead of jumping to a specific state, *n* steps ahead, ``jumpahead(n)``
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jumps to another state likely to be separated by many steps.
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.. function:: getrandbits(k)
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Returns a python :class:`long` int with *k* random bits. This method is supplied
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with the MersenneTwister generator and some other generators may also provide it
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as an optional part of the API. When available, :meth:`getrandbits` enables
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:meth:`randrange` to handle arbitrarily large ranges.
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.. versionadded:: 2.4
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Functions for integers:
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.. function:: randrange([start,] stop[, step])
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Return a randomly selected element from ``range(start, stop, step)``. This is
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equivalent to ``choice(range(start, stop, step))``, but doesn't actually build a
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range object.
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.. versionadded:: 1.5.2
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.. function:: randint(a, b)
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Return a random integer *N* such that ``a <= N <= b``.
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Functions for sequences:
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.. function:: choice(seq)
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Return a random element from the non-empty sequence *seq*. If *seq* is empty,
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raises :exc:`IndexError`.
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.. function:: shuffle(x[, random])
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Shuffle the sequence *x* in place. The optional argument *random* is a
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0-argument function returning a random float in [0.0, 1.0); by default, this is
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the function :func:`random`.
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Note that for even rather small ``len(x)``, the total number of permutations of
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*x* is larger than the period of most random number generators; this implies
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that most permutations of a long sequence can never be generated.
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.. function:: sample(population, k)
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Return a *k* length list of unique elements chosen from the population sequence.
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Used for random sampling without replacement.
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.. versionadded:: 2.3
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Returns a new list containing elements from the population while leaving the
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original population unchanged. The resulting list is in selection order so that
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all sub-slices will also be valid random samples. This allows raffle winners
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(the sample) to be partitioned into grand prize and second place winners (the
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subslices).
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Members of the population need not be :term:`hashable` or unique. If the population
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contains repeats, then each occurrence is a possible selection in the sample.
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To choose a sample from a range of integers, use an :func:`xrange` object as an
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argument. This is especially fast and space efficient for sampling from a large
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population: ``sample(xrange(10000000), 60)``.
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The following functions generate specific real-valued distributions. Function
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parameters are named after the corresponding variables in the distribution's
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equation, as used in common mathematical practice; most of these equations can
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be found in any statistics text.
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.. function:: random()
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Return the next random floating point number in the range [0.0, 1.0).
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.. function:: uniform(a, b)
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Merged revisions 68582,68718,68720-68721,68724-68727,68859,68973,69288-69289,69293,69295,69297-69301,69409,69414,69570,69573,69576,69728-69730,69769,69776,69803-69805,69840,69896 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68582 | georg.brandl | 2009-01-13 23:14:01 +0100 (Di, 13 Jan 2009) | 2 lines
Use assertRaises.
........
r68718 | georg.brandl | 2009-01-18 11:42:35 +0100 (So, 18 Jan 2009) | 1 line
#4976: union() and intersection() take multiple args, but talk about "the other".
........
r68720 | georg.brandl | 2009-01-18 11:45:22 +0100 (So, 18 Jan 2009) | 1 line
#4974: fix redundant mention of lists and tuples.
........
r68721 | georg.brandl | 2009-01-18 11:48:16 +0100 (So, 18 Jan 2009) | 1 line
#4914: trunc is in math.
........
r68724 | georg.brandl | 2009-01-18 14:24:10 +0100 (So, 18 Jan 2009) | 1 line
#4979: correct result range for some random functions.
........
r68725 | georg.brandl | 2009-01-18 14:47:26 +0100 (So, 18 Jan 2009) | 1 line
#4857: fix augmented assignment target spec.
........
r68726 | georg.brandl | 2009-01-18 15:41:52 +0100 (So, 18 Jan 2009) | 1 line
#4923: clarify what was added.
........
r68727 | georg.brandl | 2009-01-18 19:25:30 +0100 (So, 18 Jan 2009) | 1 line
#4986: augassigns are not expressions.
........
r68859 | georg.brandl | 2009-01-22 19:29:28 +0100 (Do, 22 Jan 2009) | 2 lines
Clarify wording.
........
r68973 | georg.brandl | 2009-01-26 22:29:38 +0100 (Mo, 26 Jan 2009) | 2 lines
Copy over docs on advanced role features from Sphinx docs.
........
r69288 | georg.brandl | 2009-02-05 11:30:57 +0100 (Do, 05 Feb 2009) | 1 line
#5153: fix typo in example.
........
r69289 | georg.brandl | 2009-02-05 11:37:07 +0100 (Do, 05 Feb 2009) | 1 line
#5144: document that PySys_SetArgv prepends the script directory (or the empty string) to sys.path.
........
r69293 | georg.brandl | 2009-02-05 11:59:28 +0100 (Do, 05 Feb 2009) | 1 line
#5059: fix example.
........
r69295 | georg.brandl | 2009-02-05 12:23:47 +0100 (Do, 05 Feb 2009) | 1 line
PyErr_PrintEx is also in 2.x...
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r69297 | georg.brandl | 2009-02-05 12:32:18 +0100 (Do, 05 Feb 2009) | 1 line
#5015: document PythonHome API functions.
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r69298 | georg.brandl | 2009-02-05 12:33:21 +0100 (Do, 05 Feb 2009) | 1 line
#4827: fix callback example.
........
r69299 | georg.brandl | 2009-02-05 12:35:28 +0100 (Do, 05 Feb 2009) | 1 line
#4820: use correct module for ctypes.util.
........
r69300 | georg.brandl | 2009-02-05 12:38:23 +0100 (Do, 05 Feb 2009) | 1 line
#4563: disable alpha and roman lists, fixes wrong formatting of contributor list.
........
r69301 | georg.brandl | 2009-02-05 12:40:35 +0100 (Do, 05 Feb 2009) | 1 line
#5031: fix Thread.daemon property docs.
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r69409 | georg.brandl | 2009-02-07 13:21:17 +0100 (Sa, 07 Feb 2009) | 1 line
#5174: fix wrong file closing in example.
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r69414 | georg.brandl | 2009-02-07 19:49:54 +0100 (Sa, 07 Feb 2009) | 1 line
make "super only for new-style classes" a note.
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r69570 | georg.brandl | 2009-02-13 11:40:14 +0100 (Fr, 13 Feb 2009) | 1 line
#4894: document "newurl" parameter to redirect_request().
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r69573 | georg.brandl | 2009-02-13 11:44:17 +0100 (Fr, 13 Feb 2009) | 1 line
#3734: document complex coercing behavior better.
........
r69576 | georg.brandl | 2009-02-13 11:56:50 +0100 (Fr, 13 Feb 2009) | 1 line
#1661108: note that urlsafe encoded string can contain "=".
........
r69728 | georg.brandl | 2009-02-18 01:22:55 +0100 (Mi, 18 Feb 2009) | 2 lines
#5297: fix example.
........
r69729 | georg.brandl | 2009-02-18 01:25:13 +0100 (Mi, 18 Feb 2009) | 2 lines
#5296: sequence -> iterable.
........
r69730 | georg.brandl | 2009-02-18 01:31:36 +0100 (Mi, 18 Feb 2009) | 2 lines
#5268: mention VMSError.
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r69769 | georg.brandl | 2009-02-19 09:30:06 +0100 (Do, 19 Feb 2009) | 1 line
#5310, #3558: fix operator precedence table.
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r69776 | georg.brandl | 2009-02-19 17:34:51 +0100 (Do, 19 Feb 2009) | 2 lines
#5317: update IronPython URL.
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r69803 | georg.brandl | 2009-02-20 08:48:21 +0100 (Fr, 20 Feb 2009) | 1 line
#5327: fix a broken link by joining it.
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r69804 | georg.brandl | 2009-02-20 09:22:21 +0100 (Fr, 20 Feb 2009) | 1 line
At least separate imports from other statements.
........
r69805 | georg.brandl | 2009-02-20 09:45:47 +0100 (Fr, 20 Feb 2009) | 2 lines
Fix punctuation.
........
r69840 | georg.brandl | 2009-02-21 20:09:40 +0100 (Sa, 21 Feb 2009) | 1 line
#5338, #5339: two types in the API manual.
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r69896 | georg.brandl | 2009-02-23 11:24:23 +0100 (Mo, 23 Feb 2009) | 1 line
#5348: format() converts all kinds of values.
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2009-02-23 06:41:11 -04:00
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Return a random floating point number *N* such that ``a <= N <= b`` for
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``a <= b`` and ``b <= N <= a`` for ``b < a``.
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2007-08-15 11:28:01 -03:00
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2008-03-23 10:32:32 -03:00
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.. function:: triangular(low, high, mode)
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Merged revisions 68582,68718,68720-68721,68724-68727,68859,68973,69288-69289,69293,69295,69297-69301,69409,69414,69570,69573,69576,69728-69730,69769,69776,69803-69805,69840,69896 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68582 | georg.brandl | 2009-01-13 23:14:01 +0100 (Di, 13 Jan 2009) | 2 lines
Use assertRaises.
........
r68718 | georg.brandl | 2009-01-18 11:42:35 +0100 (So, 18 Jan 2009) | 1 line
#4976: union() and intersection() take multiple args, but talk about "the other".
........
r68720 | georg.brandl | 2009-01-18 11:45:22 +0100 (So, 18 Jan 2009) | 1 line
#4974: fix redundant mention of lists and tuples.
........
r68721 | georg.brandl | 2009-01-18 11:48:16 +0100 (So, 18 Jan 2009) | 1 line
#4914: trunc is in math.
........
r68724 | georg.brandl | 2009-01-18 14:24:10 +0100 (So, 18 Jan 2009) | 1 line
#4979: correct result range for some random functions.
........
r68725 | georg.brandl | 2009-01-18 14:47:26 +0100 (So, 18 Jan 2009) | 1 line
#4857: fix augmented assignment target spec.
........
r68726 | georg.brandl | 2009-01-18 15:41:52 +0100 (So, 18 Jan 2009) | 1 line
#4923: clarify what was added.
........
r68727 | georg.brandl | 2009-01-18 19:25:30 +0100 (So, 18 Jan 2009) | 1 line
#4986: augassigns are not expressions.
........
r68859 | georg.brandl | 2009-01-22 19:29:28 +0100 (Do, 22 Jan 2009) | 2 lines
Clarify wording.
........
r68973 | georg.brandl | 2009-01-26 22:29:38 +0100 (Mo, 26 Jan 2009) | 2 lines
Copy over docs on advanced role features from Sphinx docs.
........
r69288 | georg.brandl | 2009-02-05 11:30:57 +0100 (Do, 05 Feb 2009) | 1 line
#5153: fix typo in example.
........
r69289 | georg.brandl | 2009-02-05 11:37:07 +0100 (Do, 05 Feb 2009) | 1 line
#5144: document that PySys_SetArgv prepends the script directory (or the empty string) to sys.path.
........
r69293 | georg.brandl | 2009-02-05 11:59:28 +0100 (Do, 05 Feb 2009) | 1 line
#5059: fix example.
........
r69295 | georg.brandl | 2009-02-05 12:23:47 +0100 (Do, 05 Feb 2009) | 1 line
PyErr_PrintEx is also in 2.x...
........
r69297 | georg.brandl | 2009-02-05 12:32:18 +0100 (Do, 05 Feb 2009) | 1 line
#5015: document PythonHome API functions.
........
r69298 | georg.brandl | 2009-02-05 12:33:21 +0100 (Do, 05 Feb 2009) | 1 line
#4827: fix callback example.
........
r69299 | georg.brandl | 2009-02-05 12:35:28 +0100 (Do, 05 Feb 2009) | 1 line
#4820: use correct module for ctypes.util.
........
r69300 | georg.brandl | 2009-02-05 12:38:23 +0100 (Do, 05 Feb 2009) | 1 line
#4563: disable alpha and roman lists, fixes wrong formatting of contributor list.
........
r69301 | georg.brandl | 2009-02-05 12:40:35 +0100 (Do, 05 Feb 2009) | 1 line
#5031: fix Thread.daemon property docs.
........
r69409 | georg.brandl | 2009-02-07 13:21:17 +0100 (Sa, 07 Feb 2009) | 1 line
#5174: fix wrong file closing in example.
........
r69414 | georg.brandl | 2009-02-07 19:49:54 +0100 (Sa, 07 Feb 2009) | 1 line
make "super only for new-style classes" a note.
........
r69570 | georg.brandl | 2009-02-13 11:40:14 +0100 (Fr, 13 Feb 2009) | 1 line
#4894: document "newurl" parameter to redirect_request().
........
r69573 | georg.brandl | 2009-02-13 11:44:17 +0100 (Fr, 13 Feb 2009) | 1 line
#3734: document complex coercing behavior better.
........
r69576 | georg.brandl | 2009-02-13 11:56:50 +0100 (Fr, 13 Feb 2009) | 1 line
#1661108: note that urlsafe encoded string can contain "=".
........
r69728 | georg.brandl | 2009-02-18 01:22:55 +0100 (Mi, 18 Feb 2009) | 2 lines
#5297: fix example.
........
r69729 | georg.brandl | 2009-02-18 01:25:13 +0100 (Mi, 18 Feb 2009) | 2 lines
#5296: sequence -> iterable.
........
r69730 | georg.brandl | 2009-02-18 01:31:36 +0100 (Mi, 18 Feb 2009) | 2 lines
#5268: mention VMSError.
........
r69769 | georg.brandl | 2009-02-19 09:30:06 +0100 (Do, 19 Feb 2009) | 1 line
#5310, #3558: fix operator precedence table.
........
r69776 | georg.brandl | 2009-02-19 17:34:51 +0100 (Do, 19 Feb 2009) | 2 lines
#5317: update IronPython URL.
........
r69803 | georg.brandl | 2009-02-20 08:48:21 +0100 (Fr, 20 Feb 2009) | 1 line
#5327: fix a broken link by joining it.
........
r69804 | georg.brandl | 2009-02-20 09:22:21 +0100 (Fr, 20 Feb 2009) | 1 line
At least separate imports from other statements.
........
r69805 | georg.brandl | 2009-02-20 09:45:47 +0100 (Fr, 20 Feb 2009) | 2 lines
Fix punctuation.
........
r69840 | georg.brandl | 2009-02-21 20:09:40 +0100 (Sa, 21 Feb 2009) | 1 line
#5338, #5339: two types in the API manual.
........
r69896 | georg.brandl | 2009-02-23 11:24:23 +0100 (Mo, 23 Feb 2009) | 1 line
#5348: format() converts all kinds of values.
........
2009-02-23 06:41:11 -04:00
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Return a random floating point number *N* such that ``low <= N <= high`` and
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2008-03-24 03:07:49 -03:00
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with the specified *mode* between those bounds. The *low* and *high* bounds
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default to zero and one. The *mode* argument defaults to the midpoint
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between the bounds, giving a symmetric distribution.
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2008-03-23 16:37:53 -03:00
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2008-03-24 03:07:49 -03:00
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.. versionadded:: 2.6
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2008-03-23 16:37:53 -03:00
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2007-08-15 11:28:01 -03:00
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.. function:: betavariate(alpha, beta)
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|
Merged revisions 68582,68718,68720-68721,68724-68727,68859,68973,69288-69289,69293,69295,69297-69301,69409,69414,69570,69573,69576,69728-69730,69769,69776,69803-69805,69840,69896 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68582 | georg.brandl | 2009-01-13 23:14:01 +0100 (Di, 13 Jan 2009) | 2 lines
Use assertRaises.
........
r68718 | georg.brandl | 2009-01-18 11:42:35 +0100 (So, 18 Jan 2009) | 1 line
#4976: union() and intersection() take multiple args, but talk about "the other".
........
r68720 | georg.brandl | 2009-01-18 11:45:22 +0100 (So, 18 Jan 2009) | 1 line
#4974: fix redundant mention of lists and tuples.
........
r68721 | georg.brandl | 2009-01-18 11:48:16 +0100 (So, 18 Jan 2009) | 1 line
#4914: trunc is in math.
........
r68724 | georg.brandl | 2009-01-18 14:24:10 +0100 (So, 18 Jan 2009) | 1 line
#4979: correct result range for some random functions.
........
r68725 | georg.brandl | 2009-01-18 14:47:26 +0100 (So, 18 Jan 2009) | 1 line
#4857: fix augmented assignment target spec.
........
r68726 | georg.brandl | 2009-01-18 15:41:52 +0100 (So, 18 Jan 2009) | 1 line
#4923: clarify what was added.
........
r68727 | georg.brandl | 2009-01-18 19:25:30 +0100 (So, 18 Jan 2009) | 1 line
#4986: augassigns are not expressions.
........
r68859 | georg.brandl | 2009-01-22 19:29:28 +0100 (Do, 22 Jan 2009) | 2 lines
Clarify wording.
........
r68973 | georg.brandl | 2009-01-26 22:29:38 +0100 (Mo, 26 Jan 2009) | 2 lines
Copy over docs on advanced role features from Sphinx docs.
........
r69288 | georg.brandl | 2009-02-05 11:30:57 +0100 (Do, 05 Feb 2009) | 1 line
#5153: fix typo in example.
........
r69289 | georg.brandl | 2009-02-05 11:37:07 +0100 (Do, 05 Feb 2009) | 1 line
#5144: document that PySys_SetArgv prepends the script directory (or the empty string) to sys.path.
........
r69293 | georg.brandl | 2009-02-05 11:59:28 +0100 (Do, 05 Feb 2009) | 1 line
#5059: fix example.
........
r69295 | georg.brandl | 2009-02-05 12:23:47 +0100 (Do, 05 Feb 2009) | 1 line
PyErr_PrintEx is also in 2.x...
........
r69297 | georg.brandl | 2009-02-05 12:32:18 +0100 (Do, 05 Feb 2009) | 1 line
#5015: document PythonHome API functions.
........
r69298 | georg.brandl | 2009-02-05 12:33:21 +0100 (Do, 05 Feb 2009) | 1 line
#4827: fix callback example.
........
r69299 | georg.brandl | 2009-02-05 12:35:28 +0100 (Do, 05 Feb 2009) | 1 line
#4820: use correct module for ctypes.util.
........
r69300 | georg.brandl | 2009-02-05 12:38:23 +0100 (Do, 05 Feb 2009) | 1 line
#4563: disable alpha and roman lists, fixes wrong formatting of contributor list.
........
r69301 | georg.brandl | 2009-02-05 12:40:35 +0100 (Do, 05 Feb 2009) | 1 line
#5031: fix Thread.daemon property docs.
........
r69409 | georg.brandl | 2009-02-07 13:21:17 +0100 (Sa, 07 Feb 2009) | 1 line
#5174: fix wrong file closing in example.
........
r69414 | georg.brandl | 2009-02-07 19:49:54 +0100 (Sa, 07 Feb 2009) | 1 line
make "super only for new-style classes" a note.
........
r69570 | georg.brandl | 2009-02-13 11:40:14 +0100 (Fr, 13 Feb 2009) | 1 line
#4894: document "newurl" parameter to redirect_request().
........
r69573 | georg.brandl | 2009-02-13 11:44:17 +0100 (Fr, 13 Feb 2009) | 1 line
#3734: document complex coercing behavior better.
........
r69576 | georg.brandl | 2009-02-13 11:56:50 +0100 (Fr, 13 Feb 2009) | 1 line
#1661108: note that urlsafe encoded string can contain "=".
........
r69728 | georg.brandl | 2009-02-18 01:22:55 +0100 (Mi, 18 Feb 2009) | 2 lines
#5297: fix example.
........
r69729 | georg.brandl | 2009-02-18 01:25:13 +0100 (Mi, 18 Feb 2009) | 2 lines
#5296: sequence -> iterable.
........
r69730 | georg.brandl | 2009-02-18 01:31:36 +0100 (Mi, 18 Feb 2009) | 2 lines
#5268: mention VMSError.
........
r69769 | georg.brandl | 2009-02-19 09:30:06 +0100 (Do, 19 Feb 2009) | 1 line
#5310, #3558: fix operator precedence table.
........
r69776 | georg.brandl | 2009-02-19 17:34:51 +0100 (Do, 19 Feb 2009) | 2 lines
#5317: update IronPython URL.
........
r69803 | georg.brandl | 2009-02-20 08:48:21 +0100 (Fr, 20 Feb 2009) | 1 line
#5327: fix a broken link by joining it.
........
r69804 | georg.brandl | 2009-02-20 09:22:21 +0100 (Fr, 20 Feb 2009) | 1 line
At least separate imports from other statements.
........
r69805 | georg.brandl | 2009-02-20 09:45:47 +0100 (Fr, 20 Feb 2009) | 2 lines
Fix punctuation.
........
r69840 | georg.brandl | 2009-02-21 20:09:40 +0100 (Sa, 21 Feb 2009) | 1 line
#5338, #5339: two types in the API manual.
........
r69896 | georg.brandl | 2009-02-23 11:24:23 +0100 (Mo, 23 Feb 2009) | 1 line
#5348: format() converts all kinds of values.
........
2009-02-23 06:41:11 -04:00
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Beta distribution. Conditions on the parameters are ``alpha > 0`` and
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``beta > 0``. Returned values range between 0 and 1.
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2007-08-15 11:28:01 -03:00
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.. function:: expovariate(lambd)
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Merged revisions 68292,68344,68361,68378,68424,68426,68429-68430,68450,68457,68480-68481,68493,68495,68499,68501,68512,68514-68515 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68292 | skip.montanaro | 2009-01-04 11:36:58 +0100 (So, 04 Jan 2009) | 3 lines
If user configures --without-gcc give preference to $CC instead of blindly
assuming the compiler will be "cc".
........
r68344 | marc-andre.lemburg | 2009-01-05 20:43:35 +0100 (Mo, 05 Jan 2009) | 7 lines
Fix #4846 (Py_UNICODE_ISSPACE causes linker error) by moving the declaration
into the extern "C" section.
Add a few more comments and apply some minor edits to make the file contents
fit the original structure again.
........
r68361 | antoine.pitrou | 2009-01-06 19:34:08 +0100 (Di, 06 Jan 2009) | 3 lines
Use shutil.rmtree rather than os.rmdir.
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r68378 | mark.dickinson | 2009-01-07 18:48:33 +0100 (Mi, 07 Jan 2009) | 2 lines
Issue #4869: clarify documentation for random.expovariate.
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r68424 | benjamin.peterson | 2009-01-09 03:53:35 +0100 (Fr, 09 Jan 2009) | 1 line
specify what -3 warnings are about
........
r68426 | benjamin.peterson | 2009-01-09 04:03:05 +0100 (Fr, 09 Jan 2009) | 1 line
fix spelling
........
r68429 | benjamin.peterson | 2009-01-09 04:05:14 +0100 (Fr, 09 Jan 2009) | 1 line
add -3 to manpage
........
r68430 | benjamin.peterson | 2009-01-09 04:07:27 +0100 (Fr, 09 Jan 2009) | 1 line
be more specific in -3 option help
........
r68450 | jeffrey.yasskin | 2009-01-09 17:47:07 +0100 (Fr, 09 Jan 2009) | 3 lines
Fix issue 4884, preventing a crash in the socket code when python is compiled
with llvm-gcc and run with a glibc <2.10.
........
r68457 | kristjan.jonsson | 2009-01-09 21:10:59 +0100 (Fr, 09 Jan 2009) | 1 line
Issue 3677: Fix import from UNC paths on Windows.
........
r68480 | vinay.sajip | 2009-01-10 14:38:04 +0100 (Sa, 10 Jan 2009) | 1 line
Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library.
........
r68481 | vinay.sajip | 2009-01-10 14:42:04 +0100 (Sa, 10 Jan 2009) | 1 line
Corrected an incorrect self-reference.
........
r68493 | benjamin.peterson | 2009-01-10 18:18:55 +0100 (Sa, 10 Jan 2009) | 1 line
rewrite verbose conditionals
........
r68495 | benjamin.peterson | 2009-01-10 18:36:44 +0100 (Sa, 10 Jan 2009) | 1 line
tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901
........
r68499 | mark.dickinson | 2009-01-10 20:14:55 +0100 (Sa, 10 Jan 2009) | 2 lines
Remove an unnecessary check from test_decimal.
........
r68501 | vinay.sajip | 2009-01-10 20:22:57 +0100 (Sa, 10 Jan 2009) | 1 line
Corrected minor typo and added .currentmodule directives to fix missing cross-references.
........
r68512 | benjamin.peterson | 2009-01-10 23:42:10 +0100 (Sa, 10 Jan 2009) | 1 line
make tests fail if they can't be imported
........
r68514 | benjamin.peterson | 2009-01-11 00:41:59 +0100 (So, 11 Jan 2009) | 1 line
move seealso to a more appropiate place
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r68515 | benjamin.peterson | 2009-01-11 00:49:08 +0100 (So, 11 Jan 2009) | 1 line
macos 9 isn't supported
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2009-01-13 20:00:17 -04:00
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Exponential distribution. *lambd* is 1.0 divided by the desired
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mean. It should be nonzero. (The parameter would be called
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"lambda", but that is a reserved word in Python.) Returned values
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range from 0 to positive infinity if *lambd* is positive, and from
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negative infinity to 0 if *lambd* is negative.
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2007-08-15 11:28:01 -03:00
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.. function:: gammavariate(alpha, beta)
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Merged revisions 68582,68718,68720-68721,68724-68727,68859,68973,69288-69289,69293,69295,69297-69301,69409,69414,69570,69573,69576,69728-69730,69769,69776,69803-69805,69840,69896 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68582 | georg.brandl | 2009-01-13 23:14:01 +0100 (Di, 13 Jan 2009) | 2 lines
Use assertRaises.
........
r68718 | georg.brandl | 2009-01-18 11:42:35 +0100 (So, 18 Jan 2009) | 1 line
#4976: union() and intersection() take multiple args, but talk about "the other".
........
r68720 | georg.brandl | 2009-01-18 11:45:22 +0100 (So, 18 Jan 2009) | 1 line
#4974: fix redundant mention of lists and tuples.
........
r68721 | georg.brandl | 2009-01-18 11:48:16 +0100 (So, 18 Jan 2009) | 1 line
#4914: trunc is in math.
........
r68724 | georg.brandl | 2009-01-18 14:24:10 +0100 (So, 18 Jan 2009) | 1 line
#4979: correct result range for some random functions.
........
r68725 | georg.brandl | 2009-01-18 14:47:26 +0100 (So, 18 Jan 2009) | 1 line
#4857: fix augmented assignment target spec.
........
r68726 | georg.brandl | 2009-01-18 15:41:52 +0100 (So, 18 Jan 2009) | 1 line
#4923: clarify what was added.
........
r68727 | georg.brandl | 2009-01-18 19:25:30 +0100 (So, 18 Jan 2009) | 1 line
#4986: augassigns are not expressions.
........
r68859 | georg.brandl | 2009-01-22 19:29:28 +0100 (Do, 22 Jan 2009) | 2 lines
Clarify wording.
........
r68973 | georg.brandl | 2009-01-26 22:29:38 +0100 (Mo, 26 Jan 2009) | 2 lines
Copy over docs on advanced role features from Sphinx docs.
........
r69288 | georg.brandl | 2009-02-05 11:30:57 +0100 (Do, 05 Feb 2009) | 1 line
#5153: fix typo in example.
........
r69289 | georg.brandl | 2009-02-05 11:37:07 +0100 (Do, 05 Feb 2009) | 1 line
#5144: document that PySys_SetArgv prepends the script directory (or the empty string) to sys.path.
........
r69293 | georg.brandl | 2009-02-05 11:59:28 +0100 (Do, 05 Feb 2009) | 1 line
#5059: fix example.
........
r69295 | georg.brandl | 2009-02-05 12:23:47 +0100 (Do, 05 Feb 2009) | 1 line
PyErr_PrintEx is also in 2.x...
........
r69297 | georg.brandl | 2009-02-05 12:32:18 +0100 (Do, 05 Feb 2009) | 1 line
#5015: document PythonHome API functions.
........
r69298 | georg.brandl | 2009-02-05 12:33:21 +0100 (Do, 05 Feb 2009) | 1 line
#4827: fix callback example.
........
r69299 | georg.brandl | 2009-02-05 12:35:28 +0100 (Do, 05 Feb 2009) | 1 line
#4820: use correct module for ctypes.util.
........
r69300 | georg.brandl | 2009-02-05 12:38:23 +0100 (Do, 05 Feb 2009) | 1 line
#4563: disable alpha and roman lists, fixes wrong formatting of contributor list.
........
r69301 | georg.brandl | 2009-02-05 12:40:35 +0100 (Do, 05 Feb 2009) | 1 line
#5031: fix Thread.daemon property docs.
........
r69409 | georg.brandl | 2009-02-07 13:21:17 +0100 (Sa, 07 Feb 2009) | 1 line
#5174: fix wrong file closing in example.
........
r69414 | georg.brandl | 2009-02-07 19:49:54 +0100 (Sa, 07 Feb 2009) | 1 line
make "super only for new-style classes" a note.
........
r69570 | georg.brandl | 2009-02-13 11:40:14 +0100 (Fr, 13 Feb 2009) | 1 line
#4894: document "newurl" parameter to redirect_request().
........
r69573 | georg.brandl | 2009-02-13 11:44:17 +0100 (Fr, 13 Feb 2009) | 1 line
#3734: document complex coercing behavior better.
........
r69576 | georg.brandl | 2009-02-13 11:56:50 +0100 (Fr, 13 Feb 2009) | 1 line
#1661108: note that urlsafe encoded string can contain "=".
........
r69728 | georg.brandl | 2009-02-18 01:22:55 +0100 (Mi, 18 Feb 2009) | 2 lines
#5297: fix example.
........
r69729 | georg.brandl | 2009-02-18 01:25:13 +0100 (Mi, 18 Feb 2009) | 2 lines
#5296: sequence -> iterable.
........
r69730 | georg.brandl | 2009-02-18 01:31:36 +0100 (Mi, 18 Feb 2009) | 2 lines
#5268: mention VMSError.
........
r69769 | georg.brandl | 2009-02-19 09:30:06 +0100 (Do, 19 Feb 2009) | 1 line
#5310, #3558: fix operator precedence table.
........
r69776 | georg.brandl | 2009-02-19 17:34:51 +0100 (Do, 19 Feb 2009) | 2 lines
#5317: update IronPython URL.
........
r69803 | georg.brandl | 2009-02-20 08:48:21 +0100 (Fr, 20 Feb 2009) | 1 line
#5327: fix a broken link by joining it.
........
r69804 | georg.brandl | 2009-02-20 09:22:21 +0100 (Fr, 20 Feb 2009) | 1 line
At least separate imports from other statements.
........
r69805 | georg.brandl | 2009-02-20 09:45:47 +0100 (Fr, 20 Feb 2009) | 2 lines
Fix punctuation.
........
r69840 | georg.brandl | 2009-02-21 20:09:40 +0100 (Sa, 21 Feb 2009) | 1 line
#5338, #5339: two types in the API manual.
........
r69896 | georg.brandl | 2009-02-23 11:24:23 +0100 (Mo, 23 Feb 2009) | 1 line
#5348: format() converts all kinds of values.
........
2009-02-23 06:41:11 -04:00
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Gamma distribution. (*Not* the gamma function!) Conditions on the
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parameters are ``alpha > 0`` and ``beta > 0``.
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2007-08-15 11:28:01 -03:00
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.. function:: gauss(mu, sigma)
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Merged revisions 68582,68718,68720-68721,68724-68727,68859,68973,69288-69289,69293,69295,69297-69301,69409,69414,69570,69573,69576,69728-69730,69769,69776,69803-69805,69840,69896 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68582 | georg.brandl | 2009-01-13 23:14:01 +0100 (Di, 13 Jan 2009) | 2 lines
Use assertRaises.
........
r68718 | georg.brandl | 2009-01-18 11:42:35 +0100 (So, 18 Jan 2009) | 1 line
#4976: union() and intersection() take multiple args, but talk about "the other".
........
r68720 | georg.brandl | 2009-01-18 11:45:22 +0100 (So, 18 Jan 2009) | 1 line
#4974: fix redundant mention of lists and tuples.
........
r68721 | georg.brandl | 2009-01-18 11:48:16 +0100 (So, 18 Jan 2009) | 1 line
#4914: trunc is in math.
........
r68724 | georg.brandl | 2009-01-18 14:24:10 +0100 (So, 18 Jan 2009) | 1 line
#4979: correct result range for some random functions.
........
r68725 | georg.brandl | 2009-01-18 14:47:26 +0100 (So, 18 Jan 2009) | 1 line
#4857: fix augmented assignment target spec.
........
r68726 | georg.brandl | 2009-01-18 15:41:52 +0100 (So, 18 Jan 2009) | 1 line
#4923: clarify what was added.
........
r68727 | georg.brandl | 2009-01-18 19:25:30 +0100 (So, 18 Jan 2009) | 1 line
#4986: augassigns are not expressions.
........
r68859 | georg.brandl | 2009-01-22 19:29:28 +0100 (Do, 22 Jan 2009) | 2 lines
Clarify wording.
........
r68973 | georg.brandl | 2009-01-26 22:29:38 +0100 (Mo, 26 Jan 2009) | 2 lines
Copy over docs on advanced role features from Sphinx docs.
........
r69288 | georg.brandl | 2009-02-05 11:30:57 +0100 (Do, 05 Feb 2009) | 1 line
#5153: fix typo in example.
........
r69289 | georg.brandl | 2009-02-05 11:37:07 +0100 (Do, 05 Feb 2009) | 1 line
#5144: document that PySys_SetArgv prepends the script directory (or the empty string) to sys.path.
........
r69293 | georg.brandl | 2009-02-05 11:59:28 +0100 (Do, 05 Feb 2009) | 1 line
#5059: fix example.
........
r69295 | georg.brandl | 2009-02-05 12:23:47 +0100 (Do, 05 Feb 2009) | 1 line
PyErr_PrintEx is also in 2.x...
........
r69297 | georg.brandl | 2009-02-05 12:32:18 +0100 (Do, 05 Feb 2009) | 1 line
#5015: document PythonHome API functions.
........
r69298 | georg.brandl | 2009-02-05 12:33:21 +0100 (Do, 05 Feb 2009) | 1 line
#4827: fix callback example.
........
r69299 | georg.brandl | 2009-02-05 12:35:28 +0100 (Do, 05 Feb 2009) | 1 line
#4820: use correct module for ctypes.util.
........
r69300 | georg.brandl | 2009-02-05 12:38:23 +0100 (Do, 05 Feb 2009) | 1 line
#4563: disable alpha and roman lists, fixes wrong formatting of contributor list.
........
r69301 | georg.brandl | 2009-02-05 12:40:35 +0100 (Do, 05 Feb 2009) | 1 line
#5031: fix Thread.daemon property docs.
........
r69409 | georg.brandl | 2009-02-07 13:21:17 +0100 (Sa, 07 Feb 2009) | 1 line
#5174: fix wrong file closing in example.
........
r69414 | georg.brandl | 2009-02-07 19:49:54 +0100 (Sa, 07 Feb 2009) | 1 line
make "super only for new-style classes" a note.
........
r69570 | georg.brandl | 2009-02-13 11:40:14 +0100 (Fr, 13 Feb 2009) | 1 line
#4894: document "newurl" parameter to redirect_request().
........
r69573 | georg.brandl | 2009-02-13 11:44:17 +0100 (Fr, 13 Feb 2009) | 1 line
#3734: document complex coercing behavior better.
........
r69576 | georg.brandl | 2009-02-13 11:56:50 +0100 (Fr, 13 Feb 2009) | 1 line
#1661108: note that urlsafe encoded string can contain "=".
........
r69728 | georg.brandl | 2009-02-18 01:22:55 +0100 (Mi, 18 Feb 2009) | 2 lines
#5297: fix example.
........
r69729 | georg.brandl | 2009-02-18 01:25:13 +0100 (Mi, 18 Feb 2009) | 2 lines
#5296: sequence -> iterable.
........
r69730 | georg.brandl | 2009-02-18 01:31:36 +0100 (Mi, 18 Feb 2009) | 2 lines
#5268: mention VMSError.
........
r69769 | georg.brandl | 2009-02-19 09:30:06 +0100 (Do, 19 Feb 2009) | 1 line
#5310, #3558: fix operator precedence table.
........
r69776 | georg.brandl | 2009-02-19 17:34:51 +0100 (Do, 19 Feb 2009) | 2 lines
#5317: update IronPython URL.
........
r69803 | georg.brandl | 2009-02-20 08:48:21 +0100 (Fr, 20 Feb 2009) | 1 line
#5327: fix a broken link by joining it.
........
r69804 | georg.brandl | 2009-02-20 09:22:21 +0100 (Fr, 20 Feb 2009) | 1 line
At least separate imports from other statements.
........
r69805 | georg.brandl | 2009-02-20 09:45:47 +0100 (Fr, 20 Feb 2009) | 2 lines
Fix punctuation.
........
r69840 | georg.brandl | 2009-02-21 20:09:40 +0100 (Sa, 21 Feb 2009) | 1 line
#5338, #5339: two types in the API manual.
........
r69896 | georg.brandl | 2009-02-23 11:24:23 +0100 (Mo, 23 Feb 2009) | 1 line
#5348: format() converts all kinds of values.
........
2009-02-23 06:41:11 -04:00
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Gaussian distribution. *mu* is the mean, and *sigma* is the standard
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deviation. This is slightly faster than the :func:`normalvariate` function
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defined below.
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2007-08-15 11:28:01 -03:00
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.. function:: lognormvariate(mu, sigma)
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Log normal distribution. If you take the natural logarithm of this
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distribution, you'll get a normal distribution with mean *mu* and standard
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deviation *sigma*. *mu* can have any value, and *sigma* must be greater than
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zero.
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.. function:: normalvariate(mu, sigma)
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Normal distribution. *mu* is the mean, and *sigma* is the standard deviation.
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.. function:: vonmisesvariate(mu, kappa)
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*mu* is the mean angle, expressed in radians between 0 and 2\*\ *pi*, and *kappa*
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is the concentration parameter, which must be greater than or equal to zero. If
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*kappa* is equal to zero, this distribution reduces to a uniform random angle
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over the range 0 to 2\*\ *pi*.
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.. function:: paretovariate(alpha)
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Pareto distribution. *alpha* is the shape parameter.
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.. function:: weibullvariate(alpha, beta)
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Weibull distribution. *alpha* is the scale parameter and *beta* is the shape
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parameter.
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Alternative Generators:
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.. class:: WichmannHill([seed])
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Class that implements the Wichmann-Hill algorithm as the core generator. Has all
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of the same methods as :class:`Random` plus the :meth:`whseed` method described
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below. Because this class is implemented in pure Python, it is not threadsafe
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and may require locks between calls. The period of the generator is
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6,953,607,871,644 which is small enough to require care that two independent
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random sequences do not overlap.
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.. function:: whseed([x])
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This is obsolete, supplied for bit-level compatibility with versions of Python
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prior to 2.1. See :func:`seed` for details. :func:`whseed` does not guarantee
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that distinct integer arguments yield distinct internal states, and can yield no
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more than about 2\*\*24 distinct internal states in all.
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.. class:: SystemRandom([seed])
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Class that uses the :func:`os.urandom` function for generating random numbers
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from sources provided by the operating system. Not available on all systems.
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Does not rely on software state and sequences are not reproducible. Accordingly,
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the :meth:`seed` and :meth:`jumpahead` methods have no effect and are ignored.
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The :meth:`getstate` and :meth:`setstate` methods raise
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:exc:`NotImplementedError` if called.
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.. versionadded:: 2.4
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Examples of basic usage::
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>>> random.random() # Random float x, 0.0 <= x < 1.0
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0.37444887175646646
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>>> random.uniform(1, 10) # Random float x, 1.0 <= x < 10.0
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1.1800146073117523
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>>> random.randint(1, 10) # Integer from 1 to 10, endpoints included
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7
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>>> random.randrange(0, 101, 2) # Even integer from 0 to 100
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26
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>>> random.choice('abcdefghij') # Choose a random element
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'c'
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>>> items = [1, 2, 3, 4, 5, 6, 7]
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>>> random.shuffle(items)
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>>> items
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[7, 3, 2, 5, 6, 4, 1]
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>>> random.sample([1, 2, 3, 4, 5], 3) # Choose 3 elements
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[4, 1, 5]
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.. seealso::
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M. Matsumoto and T. Nishimura, "Mersenne Twister: A 623-dimensionally
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equidistributed uniform pseudorandom number generator", ACM Transactions on
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Modeling and Computer Simulation Vol. 8, No. 1, January pp.3-30 1998.
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Wichmann, B. A. & Hill, I. D., "Algorithm AS 183: An efficient and portable
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pseudo-random number generator", Applied Statistics 31 (1982) 188-190.
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