cpython/Doc/library/random.rst

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:mod:`random` --- Generate pseudo-random numbers
================================================
.. module:: random
:synopsis: Generate pseudo-random numbers with various common distributions.
This module implements pseudo-random number generators for various
distributions.
For integers, uniform selection from a range. For sequences, uniform selection
of a random element, a function to generate a random permutation of a list
in-place, and a function for random sampling without replacement.
On the real line, there are functions to compute uniform, normal (Gaussian),
lognormal, negative exponential, gamma, and beta distributions. For generating
distributions of angles, the von Mises distribution is available.
Almost all module functions depend on the basic function :func:`random`, which
generates a random float uniformly in the semi-open range [0.0, 1.0). Python
uses the Mersenne Twister as the core generator. It produces 53-bit precision
floats and has a period of 2\*\*19937-1. The underlying implementation in C is
both fast and threadsafe. The Mersenne Twister is one of the most extensively
tested random number generators in existence. However, being completely
deterministic, it is not suitable for all purposes, and is completely unsuitable
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.
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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`, and :meth:`setstate`.
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.
Bookkeeping functions:
.. function:: seed([x])
Initialize the basic random number generator. Optional argument *x* can be any
Merged revisions 58742-58816 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r58745 | georg.brandl | 2007-11-01 10:19:33 -0700 (Thu, 01 Nov 2007) | 2 lines #1364: os.lstat is available on Windows too, as an alias to os.stat. ........ r58750 | christian.heimes | 2007-11-01 12:48:10 -0700 (Thu, 01 Nov 2007) | 1 line Backport of import tests for bug http://bugs.python.org/issue1293 and bug http://bugs.python.org/issue1342 ........ r58751 | christian.heimes | 2007-11-01 13:11:06 -0700 (Thu, 01 Nov 2007) | 1 line Removed non ASCII text from test as requested by Guido. Sorry :/ ........ r58753 | georg.brandl | 2007-11-01 13:37:02 -0700 (Thu, 01 Nov 2007) | 2 lines Fix markup glitch. ........ r58757 | gregory.p.smith | 2007-11-01 14:08:14 -0700 (Thu, 01 Nov 2007) | 4 lines Fix bug introduced in revision 58385. Database keys could no longer have NULL bytes in them. Replace the errant strdup with a malloc+memcpy. Adds a unit test for the correct behavior. ........ r58758 | gregory.p.smith | 2007-11-01 14:15:36 -0700 (Thu, 01 Nov 2007) | 3 lines Undo revision 58533 58534 fixes. Those were a workaround for a problem introduced by 58385. ........ r58759 | gregory.p.smith | 2007-11-01 14:17:47 -0700 (Thu, 01 Nov 2007) | 2 lines false "fix" undone as correct problem was found and fixed. ........ r58765 | mark.summerfield | 2007-11-02 01:24:59 -0700 (Fri, 02 Nov 2007) | 3 lines Added more file-handling related cross-references. ........ r58766 | nick.coghlan | 2007-11-02 03:09:12 -0700 (Fri, 02 Nov 2007) | 1 line Fix for bug 1705170 - contextmanager swallowing StopIteration (2.5 backport candidate) ........ r58784 | thomas.heller | 2007-11-02 12:10:24 -0700 (Fri, 02 Nov 2007) | 4 lines Issue #1292: On alpha, arm, ppc, and s390 linux systems the --with-system-ffi configure option defaults to "yes" because the bundled libffi sources are too old. ........ r58785 | thomas.heller | 2007-11-02 12:11:23 -0700 (Fri, 02 Nov 2007) | 1 line Enable the full ctypes c_longdouble tests again. ........ r58796 | georg.brandl | 2007-11-02 13:06:17 -0700 (Fri, 02 Nov 2007) | 4 lines Make "hashable" a glossary entry and clarify docs on __cmp__, __eq__ and __hash__. I hope the concept of hashability is better understandable now. Thanks to Tim Hatch for pointing out the flaws here. ........
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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
first imported. If randomness sources are provided by the operating system,
they are used instead of the system time (see the :func:`os.urandom` function
for details on availability).
If *x* is not ``None`` or an int, ``hash(x)`` is used instead. If *x* is an
int, *x* is used directly.
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.. function:: getstate()
Return an object capturing the current internal state of the generator. This
object can be passed to :func:`setstate` to restore the state.
.. function:: setstate(state)
*state* should have been obtained from a previous call to :func:`getstate`, and
:func:`setstate` restores the internal state of the generator to what it was at
the time :func:`setstate` was called.
Merged revisions 60481,60485,60489-60492,60494-60496,60498-60499,60501-60503,60505-60506,60508-60509,60523-60524,60532,60543,60545,60547-60548,60552,60554,60556-60559,60561-60562,60569,60571-60572,60574,60576-60583,60585-60586,60589,60591,60594-60595,60597-60598,60600-60601,60606-60612,60615,60617,60619-60621,60623-60625,60627-60629,60631,60633,60635,60647,60650,60652,60654,60656,60658-60659,60664-60666,60668-60670,60672,60676,60678,60680-60683,60685-60686,60688,60690,60692-60694,60697-60700,60705-60706,60708,60711,60714,60720,60724-60730,60732,60736,60742,60744,60746,60748,60750-60751,60753,60756-60757,60759-60761,60763-60764,60766,60769-60770,60774-60784,60787-60789,60793,60796,60799-60809,60812-60813,60815-60821,60823-60826,60828-60829,60831-60834,60836,60838-60839,60846-60849,60852-60854,60856-60859,60861-60870,60874-60875,60880-60881,60886,60888-60890,60892,60894-60898,60900-60931,60933-60958 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r60901 | eric.smith | 2008-02-19 14:21:56 +0100 (Tue, 19 Feb 2008) | 1 line Added PEP 3101. ........ r60907 | georg.brandl | 2008-02-20 20:12:36 +0100 (Wed, 20 Feb 2008) | 2 lines Fixes contributed by Ori Avtalion. ........ r60909 | eric.smith | 2008-02-21 00:34:22 +0100 (Thu, 21 Feb 2008) | 1 line Trim leading zeros from a floating point exponent, per C99. See issue 1600. As far as I know, this only affects Windows. Add float type 'n' to PyOS_ascii_formatd (see PEP 3101 for 'n' description). ........ r60910 | eric.smith | 2008-02-21 00:39:28 +0100 (Thu, 21 Feb 2008) | 1 line Now that PyOS_ascii_formatd supports the 'n' format, simplify the float formatting code to just call it. ........ r60918 | andrew.kuchling | 2008-02-21 15:23:38 +0100 (Thu, 21 Feb 2008) | 2 lines Close manifest file. This change doesn't make any difference to CPython, but is a necessary fix for Jython. ........ r60921 | guido.van.rossum | 2008-02-21 18:46:16 +0100 (Thu, 21 Feb 2008) | 2 lines Remove news about float repr() -- issue 1580 is still in limbo. ........ r60923 | guido.van.rossum | 2008-02-21 19:18:37 +0100 (Thu, 21 Feb 2008) | 5 lines Removed uses of dict.has_key() from distutils, and uses of callable() from copy_reg.py, so the interpreter now starts up without warnings when '-3' is given. More work like this needs to be done in the rest of the stdlib. ........ r60924 | thomas.heller | 2008-02-21 19:28:48 +0100 (Thu, 21 Feb 2008) | 4 lines configure.ac: Remove the configure check for _Bool, it is already done in the top-level Python configure script. configure, fficonfig.h.in: regenerated. ........ r60925 | thomas.heller | 2008-02-21 19:52:20 +0100 (Thu, 21 Feb 2008) | 3 lines Replace 'has_key()' with 'in'. Replace 'raise Error, stuff' with 'raise Error(stuff)'. ........ r60927 | raymond.hettinger | 2008-02-21 20:24:53 +0100 (Thu, 21 Feb 2008) | 1 line Update more instances of has_key(). ........ r60928 | guido.van.rossum | 2008-02-21 20:46:35 +0100 (Thu, 21 Feb 2008) | 3 lines Fix a few typos and layout glitches (more work is needed). Move 2.5 news to Misc/HISTORY. ........ r60936 | georg.brandl | 2008-02-21 21:33:38 +0100 (Thu, 21 Feb 2008) | 2 lines #2079: typo in userdict docs. ........ r60938 | georg.brandl | 2008-02-21 21:38:13 +0100 (Thu, 21 Feb 2008) | 2 lines Part of #2154: minimal syntax fixes in doc example snippets. ........ r60942 | raymond.hettinger | 2008-02-22 04:16:42 +0100 (Fri, 22 Feb 2008) | 1 line First draft for itertools.product(). Docs and other updates forthcoming. ........ r60955 | nick.coghlan | 2008-02-22 11:54:06 +0100 (Fri, 22 Feb 2008) | 1 line Try to make command line error messages from runpy easier to understand (and suppress traceback cruft from the implicitly invoked runpy machinery) ........ r60956 | georg.brandl | 2008-02-22 13:31:45 +0100 (Fri, 22 Feb 2008) | 2 lines A lot more typo fixes by Ori Avtalion. ........ r60957 | georg.brandl | 2008-02-22 13:56:34 +0100 (Fri, 22 Feb 2008) | 2 lines Don't reference pyshell. ........ r60958 | georg.brandl | 2008-02-22 13:57:05 +0100 (Fri, 22 Feb 2008) | 2 lines Another fix. ........
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.. 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
conjunction 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.
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.. function:: getrandbits(k)
Returns a python integer with *k* random bits. This method is supplied 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
:meth:`randrange` to handle arbitrarily large ranges.
Functions for integers:
.. function:: randrange([start,] stop[, step])
Return a randomly selected element from ``range(start, stop, step)``. This is
equivalent to ``choice(range(start, stop, step))``, but doesn't actually build a
range object.
.. function:: randint(a, b)
Return a random integer *N* such that ``a <= N <= b``.
Functions for sequences:
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.. function:: choice(seq)
Return a random element from the non-empty sequence *seq*. If *seq* is empty,
raises :exc:`IndexError`.
.. function:: shuffle(x[, random])
Shuffle the sequence *x* in place. The optional argument *random* is a
0-argument function returning a random float in [0.0, 1.0); by default, this is
the function :func:`random`.
Note that for even rather small ``len(x)``, the total number of permutations of
*x* is larger than the period of most random number generators; this implies
that most permutations of a long sequence can never be generated.
.. function:: sample(population, k)
Return a *k* length list of unique elements chosen from the population sequence
or set. Used for random sampling without replacement.
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Returns a new list containing elements from the population while leaving the
original population unchanged. The resulting list is in selection order so that
all sub-slices will also be valid random samples. This allows raffle winners
(the sample) to be partitioned into grand prize and second place winners (the
subslices).
Merged revisions 58742-58816 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r58745 | georg.brandl | 2007-11-01 10:19:33 -0700 (Thu, 01 Nov 2007) | 2 lines #1364: os.lstat is available on Windows too, as an alias to os.stat. ........ r58750 | christian.heimes | 2007-11-01 12:48:10 -0700 (Thu, 01 Nov 2007) | 1 line Backport of import tests for bug http://bugs.python.org/issue1293 and bug http://bugs.python.org/issue1342 ........ r58751 | christian.heimes | 2007-11-01 13:11:06 -0700 (Thu, 01 Nov 2007) | 1 line Removed non ASCII text from test as requested by Guido. Sorry :/ ........ r58753 | georg.brandl | 2007-11-01 13:37:02 -0700 (Thu, 01 Nov 2007) | 2 lines Fix markup glitch. ........ r58757 | gregory.p.smith | 2007-11-01 14:08:14 -0700 (Thu, 01 Nov 2007) | 4 lines Fix bug introduced in revision 58385. Database keys could no longer have NULL bytes in them. Replace the errant strdup with a malloc+memcpy. Adds a unit test for the correct behavior. ........ r58758 | gregory.p.smith | 2007-11-01 14:15:36 -0700 (Thu, 01 Nov 2007) | 3 lines Undo revision 58533 58534 fixes. Those were a workaround for a problem introduced by 58385. ........ r58759 | gregory.p.smith | 2007-11-01 14:17:47 -0700 (Thu, 01 Nov 2007) | 2 lines false "fix" undone as correct problem was found and fixed. ........ r58765 | mark.summerfield | 2007-11-02 01:24:59 -0700 (Fri, 02 Nov 2007) | 3 lines Added more file-handling related cross-references. ........ r58766 | nick.coghlan | 2007-11-02 03:09:12 -0700 (Fri, 02 Nov 2007) | 1 line Fix for bug 1705170 - contextmanager swallowing StopIteration (2.5 backport candidate) ........ r58784 | thomas.heller | 2007-11-02 12:10:24 -0700 (Fri, 02 Nov 2007) | 4 lines Issue #1292: On alpha, arm, ppc, and s390 linux systems the --with-system-ffi configure option defaults to "yes" because the bundled libffi sources are too old. ........ r58785 | thomas.heller | 2007-11-02 12:11:23 -0700 (Fri, 02 Nov 2007) | 1 line Enable the full ctypes c_longdouble tests again. ........ r58796 | georg.brandl | 2007-11-02 13:06:17 -0700 (Fri, 02 Nov 2007) | 4 lines Make "hashable" a glossary entry and clarify docs on __cmp__, __eq__ and __hash__. I hope the concept of hashability is better understandable now. Thanks to Tim Hatch for pointing out the flaws here. ........
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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.
To choose a sample from a range of integers, use an :func:`range` object as an
argument. This is especially fast and space efficient for sampling from a large
population: ``sample(range(10000000), 60)``.
The following functions generate specific real-valued distributions. Function
parameters are named after the corresponding variables in the distribution's
equation, as used in common mathematical practice; most of these equations can
be found in any statistics text.
.. function:: random()
Return the next random floating point number in the range [0.0, 1.0).
.. function:: uniform(a, b)
Merged revisions 66508,66510,66512-66513,66523-66526,66529-66530,66532,66535,66538,66544,66546 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r66508 | benjamin.peterson | 2008-09-18 18:20:28 -0500 (Thu, 18 Sep 2008) | 1 line tabify ........ r66510 | josiah.carlson | 2008-09-18 21:07:22 -0500 (Thu, 18 Sep 2008) | 2 lines Fix for documentation bug. Fixes issue 3904. ........ r66512 | raymond.hettinger | 2008-09-19 03:07:48 -0500 (Fri, 19 Sep 2008) | 1 line Improve docs for super(). ........ r66513 | lars.gustaebel | 2008-09-19 07:39:23 -0500 (Fri, 19 Sep 2008) | 2 lines Correct information about the tarfile module. ........ r66523 | georg.brandl | 2008-09-21 02:14:44 -0500 (Sun, 21 Sep 2008) | 2 lines #3852: fix some select.kqueue and kevent docs. ........ r66524 | georg.brandl | 2008-09-21 02:15:59 -0500 (Sun, 21 Sep 2008) | 2 lines #3912: document default for *places* arg. ........ r66525 | georg.brandl | 2008-09-21 02:17:00 -0500 (Sun, 21 Sep 2008) | 2 lines #3916: fixes for docs wrt. Windows directory layout ........ r66526 | georg.brandl | 2008-09-21 02:18:28 -0500 (Sun, 21 Sep 2008) | 2 lines #3914: add //= to the augmented assign operators. ........ r66529 | georg.brandl | 2008-09-21 02:24:11 -0500 (Sun, 21 Sep 2008) | 2 lines #3901: bsddb fix. ........ r66530 | georg.brandl | 2008-09-21 02:31:52 -0500 (Sun, 21 Sep 2008) | 2 lines #3897: _collections now has an underscore. ........ r66532 | georg.brandl | 2008-09-21 02:36:22 -0500 (Sun, 21 Sep 2008) | 2 lines Update readme and Makefile (web builder doesn't exist). ........ r66535 | georg.brandl | 2008-09-21 03:03:21 -0500 (Sun, 21 Sep 2008) | 2 lines #3918: note that uniform() args can be swapped. ........ r66538 | georg.brandl | 2008-09-21 05:03:39 -0500 (Sun, 21 Sep 2008) | 2 lines Add "dist" target. ........ r66544 | benjamin.peterson | 2008-09-21 16:27:51 -0500 (Sun, 21 Sep 2008) | 4 lines #3879 fix a regression in urllib.getproxies_environment reviewers: Benjamin, Georg ........ r66546 | georg.brandl | 2008-09-21 17:31:59 -0500 (Sun, 21 Sep 2008) | 2 lines Fill out download page. ........
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Return a random floating point number *N* such that ``a <= N < b`` for
``a <= b`` and ``b <= N < a`` for ``b < a``.
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Merged revisions 61724-61725,61731-61735,61737,61739,61741,61743-61744,61753,61761,61765-61767,61769,61773,61776-61778,61780-61783,61788,61793,61796,61807,61813 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ................ r61724 | martin.v.loewis | 2008-03-22 01:01:12 +0100 (Sat, 22 Mar 2008) | 49 lines Merged revisions 61602-61723 via svnmerge from svn+ssh://pythondev@svn.python.org/sandbox/trunk/2to3/lib2to3 ........ r61626 | david.wolever | 2008-03-19 17:19:16 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added fixer for implicit local imports. See #2414. ........ r61628 | david.wolever | 2008-03-19 17:57:43 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added a class for tests which should not run if a particular import is found. ........ r61629 | collin.winter | 2008-03-19 17:58:19 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Two more relative import fixes in pgen2. ........ r61635 | david.wolever | 2008-03-19 20:16:03 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Fixed print fixer so it will do the Right Thing when it encounters __future__.print_function. 2to3 gets upset, though, so the tests have been commented out. ........ r61637 | david.wolever | 2008-03-19 21:37:17 +0100 (Mi, 19 M?\195?\164r 2008) | 3 lines Added a fixer for itertools imports (from itertools import imap, ifilterfalse --> from itertools import filterfalse) ........ r61645 | david.wolever | 2008-03-19 23:22:35 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line SVN is happier when you add the files you create... -_-' ........ r61654 | david.wolever | 2008-03-20 01:09:56 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added an explicit sort order to fixers -- fixes problems like #2427 ........ r61664 | david.wolever | 2008-03-20 04:32:40 +0100 (Do, 20 M?\195?\164r 2008) | 3 lines Fixes #2428 -- comments are no longer eatten by __future__ fixer. ........ r61673 | david.wolever | 2008-03-20 17:22:40 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added 2to3 node pretty-printer ........ r61679 | david.wolever | 2008-03-20 20:50:42 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Made node printing a little bit prettier ........ r61723 | martin.v.loewis | 2008-03-22 00:59:27 +0100 (Sa, 22 M?\195?\164r 2008) | 2 lines Fix whitespace. ........ ................ r61725 | martin.v.loewis | 2008-03-22 01:02:41 +0100 (Sat, 22 Mar 2008) | 2 lines Install lib2to3. ................ r61731 | facundo.batista | 2008-03-22 03:45:37 +0100 (Sat, 22 Mar 2008) | 4 lines Small fix that complicated the test actually when that test failed. ................ r61732 | alexandre.vassalotti | 2008-03-22 05:08:44 +0100 (Sat, 22 Mar 2008) | 2 lines Added warning for the removal of 'hotshot' in Py3k. ................ r61733 | georg.brandl | 2008-03-22 11:07:29 +0100 (Sat, 22 Mar 2008) | 4 lines #1918: document that weak references *to* an object are cleared before the object's __del__ is called, to ensure that the weak reference callback (if any) finds the object healthy. ................ r61734 | georg.brandl | 2008-03-22 11:56:23 +0100 (Sat, 22 Mar 2008) | 2 lines Activate the Sphinx doctest extension and convert howto/functional to use it. ................ r61735 | georg.brandl | 2008-03-22 11:58:38 +0100 (Sat, 22 Mar 2008) | 2 lines Allow giving source names on the cmdline. ................ r61737 | georg.brandl | 2008-03-22 12:00:48 +0100 (Sat, 22 Mar 2008) | 2 lines Fixup this HOWTO's doctest blocks so that they can be run with sphinx' doctest builder. ................ r61739 | georg.brandl | 2008-03-22 12:47:10 +0100 (Sat, 22 Mar 2008) | 2 lines Test decimal.rst doctests as far as possible with sphinx doctest. ................ r61741 | georg.brandl | 2008-03-22 13:04:26 +0100 (Sat, 22 Mar 2008) | 2 lines Make doctests in re docs usable with sphinx' doctest. ................ r61743 | georg.brandl | 2008-03-22 13:59:37 +0100 (Sat, 22 Mar 2008) | 2 lines Make more doctests in pprint docs testable. ................ r61744 | georg.brandl | 2008-03-22 14:07:06 +0100 (Sat, 22 Mar 2008) | 2 lines No need to specify explicit "doctest_block" anymore. ................ r61753 | georg.brandl | 2008-03-22 21:08:43 +0100 (Sat, 22 Mar 2008) | 2 lines Fix-up syntax problems. ................ r61761 | georg.brandl | 2008-03-22 22:06:20 +0100 (Sat, 22 Mar 2008) | 4 lines Make collections' doctests executable. (The <BLANKLINE>s will be stripped from presentation output.) ................ r61765 | georg.brandl | 2008-03-22 22:21:57 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in datetime docs. ................ r61766 | georg.brandl | 2008-03-22 22:26:44 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in operator docs. ................ r61767 | georg.brandl | 2008-03-22 22:38:33 +0100 (Sat, 22 Mar 2008) | 2 lines Enable doctests in functions.rst. Already found two errors :) ................ r61769 | georg.brandl | 2008-03-22 23:04:10 +0100 (Sat, 22 Mar 2008) | 3 lines Enable doctest running for several other documents. We have now over 640 doctests that are run with "make doctest". ................ r61773 | raymond.hettinger | 2008-03-23 01:55:46 +0100 (Sun, 23 Mar 2008) | 1 line Simplify demo code. ................ r61776 | neal.norwitz | 2008-03-23 04:43:33 +0100 (Sun, 23 Mar 2008) | 7 lines Try to make this test a little more robust and not fail with: timeout (10.0025) is more than 2 seconds more than expected (0.001) I'm assuming this problem is caused by DNS lookup. This change does a DNS lookup of the hostname before trying to connect, so the time is not included. ................ r61777 | neal.norwitz | 2008-03-23 05:08:30 +0100 (Sun, 23 Mar 2008) | 1 line Speed up the test by avoiding socket timeouts. ................ r61778 | neal.norwitz | 2008-03-23 05:43:09 +0100 (Sun, 23 Mar 2008) | 1 line Skip the epoll test if epoll() does not work ................ r61780 | neal.norwitz | 2008-03-23 06:47:20 +0100 (Sun, 23 Mar 2008) | 1 line Suppress failure (to avoid a flaky test) if we cannot connect to svn.python.org ................ r61781 | neal.norwitz | 2008-03-23 07:13:25 +0100 (Sun, 23 Mar 2008) | 4 lines Move itertools before future_builtins since the latter depends on the former. From a clean build importing future_builtins would fail since itertools wasn't built yet. ................ r61782 | neal.norwitz | 2008-03-23 07:16:04 +0100 (Sun, 23 Mar 2008) | 1 line Try to prevent the alarm going off early in tearDown ................ r61783 | neal.norwitz | 2008-03-23 07:19:57 +0100 (Sun, 23 Mar 2008) | 4 lines Remove compiler warnings (on Alpha at least) about using chars as array subscripts. Using chars are dangerous b/c they are signed on some platforms and unsigned on others. ................ r61788 | georg.brandl | 2008-03-23 09:05:30 +0100 (Sun, 23 Mar 2008) | 2 lines Make the doctests presentation-friendlier. ................ r61793 | amaury.forgeotdarc | 2008-03-23 10:55:29 +0100 (Sun, 23 Mar 2008) | 4 lines #1477: ur'\U0010FFFF' raised in narrow unicode builds. Corrected the raw-unicode-escape codec to use UTF-16 surrogates in this case, just like the unicode-escape codec. ................ r61796 | raymond.hettinger | 2008-03-23 14:32:32 +0100 (Sun, 23 Mar 2008) | 1 line Issue 1681432: Add triangular distribution the random module. ................ r61807 | raymond.hettinger | 2008-03-23 20:37:53 +0100 (Sun, 23 Mar 2008) | 4 lines Adopt Nick's suggestion for useful default arguments. Clean-up floating point issues by adding true division and float constants. ................ r61813 | gregory.p.smith | 2008-03-23 22:04:43 +0100 (Sun, 23 Mar 2008) | 6 lines Fix gzip to deal with CRC's being signed values in Python 2.x properly and to read 32bit values as unsigned to start with rather than applying signedness fixups allover the place afterwards. This hopefully fixes the test_tarfile failure on the alpha/tru64 buildbot. ................
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.. function:: triangular(low, high, mode)
Merged revisions 61834,61841-61842,61851-61853,61863-61864,61869-61870,61874,61889 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r61834 | raymond.hettinger | 2008-03-24 07:07:49 +0100 (Mon, 24 Mar 2008) | 1 line Tighten documentation for Random.triangular. ........ r61841 | raymond.hettinger | 2008-03-24 09:17:39 +0100 (Mon, 24 Mar 2008) | 1 line Issue 2460: Make Ellipsis objects copyable. ........ r61842 | georg.brandl | 2008-03-24 10:34:34 +0100 (Mon, 24 Mar 2008) | 2 lines #1700821: add a note to audioop docs about signedness of sample formats. ........ r61851 | christian.heimes | 2008-03-24 20:57:42 +0100 (Mon, 24 Mar 2008) | 1 line Added quick hack for bzr ........ r61852 | christian.heimes | 2008-03-24 20:58:17 +0100 (Mon, 24 Mar 2008) | 1 line Added quick hack for bzr ........ r61853 | amaury.forgeotdarc | 2008-03-24 22:04:10 +0100 (Mon, 24 Mar 2008) | 4 lines Issue2469: Correct a typo I introduced at r61793: compilation error with UCS4 builds. All buildbots compile with UCS2... ........ r61863 | neal.norwitz | 2008-03-25 05:17:38 +0100 (Tue, 25 Mar 2008) | 2 lines Fix a bunch of UnboundLocalErrors when the tests fail. ........ r61864 | neal.norwitz | 2008-03-25 05:18:18 +0100 (Tue, 25 Mar 2008) | 2 lines Try to fix a bunch of compiler warnings on Win64. ........ r61869 | neal.norwitz | 2008-03-25 07:35:10 +0100 (Tue, 25 Mar 2008) | 3 lines Don't try to close a non-open file. Don't let file removal cause the test to fail. ........ r61870 | neal.norwitz | 2008-03-25 08:00:39 +0100 (Tue, 25 Mar 2008) | 7 lines Try to get this test to be more stable: * disable gc during the test run because we are spawning objects and there was an exception when calling Popen.__del__ * Always set an alarm handler so the process doesn't exit if the test fails (should probably add assertions on the value of hndl_called in more places) * Using a negative time causes Linux to treat it as zero, so disable that test. ........ r61874 | gregory.p.smith | 2008-03-25 08:31:28 +0100 (Tue, 25 Mar 2008) | 2 lines Use a 32-bit unsigned int here, a long is not needed. ........ r61889 | georg.brandl | 2008-03-25 12:59:51 +0100 (Tue, 25 Mar 2008) | 2 lines Move declarations to block start. ........
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Return a random floating point number *N* such that ``low <= N < high`` and
with the specified *mode* between those bounds. The *low* and *high* bounds
default to zero and one. The *mode* argument defaults to the midpoint
between the bounds, giving a symmetric distribution.
Merged revisions 61724-61725,61731-61735,61737,61739,61741,61743-61744,61753,61761,61765-61767,61769,61773,61776-61778,61780-61783,61788,61793,61796,61807,61813 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ................ r61724 | martin.v.loewis | 2008-03-22 01:01:12 +0100 (Sat, 22 Mar 2008) | 49 lines Merged revisions 61602-61723 via svnmerge from svn+ssh://pythondev@svn.python.org/sandbox/trunk/2to3/lib2to3 ........ r61626 | david.wolever | 2008-03-19 17:19:16 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added fixer for implicit local imports. See #2414. ........ r61628 | david.wolever | 2008-03-19 17:57:43 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Added a class for tests which should not run if a particular import is found. ........ r61629 | collin.winter | 2008-03-19 17:58:19 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Two more relative import fixes in pgen2. ........ r61635 | david.wolever | 2008-03-19 20:16:03 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line Fixed print fixer so it will do the Right Thing when it encounters __future__.print_function. 2to3 gets upset, though, so the tests have been commented out. ........ r61637 | david.wolever | 2008-03-19 21:37:17 +0100 (Mi, 19 M?\195?\164r 2008) | 3 lines Added a fixer for itertools imports (from itertools import imap, ifilterfalse --> from itertools import filterfalse) ........ r61645 | david.wolever | 2008-03-19 23:22:35 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line SVN is happier when you add the files you create... -_-' ........ r61654 | david.wolever | 2008-03-20 01:09:56 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added an explicit sort order to fixers -- fixes problems like #2427 ........ r61664 | david.wolever | 2008-03-20 04:32:40 +0100 (Do, 20 M?\195?\164r 2008) | 3 lines Fixes #2428 -- comments are no longer eatten by __future__ fixer. ........ r61673 | david.wolever | 2008-03-20 17:22:40 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Added 2to3 node pretty-printer ........ r61679 | david.wolever | 2008-03-20 20:50:42 +0100 (Do, 20 M?\195?\164r 2008) | 1 line Made node printing a little bit prettier ........ r61723 | martin.v.loewis | 2008-03-22 00:59:27 +0100 (Sa, 22 M?\195?\164r 2008) | 2 lines Fix whitespace. ........ ................ r61725 | martin.v.loewis | 2008-03-22 01:02:41 +0100 (Sat, 22 Mar 2008) | 2 lines Install lib2to3. ................ r61731 | facundo.batista | 2008-03-22 03:45:37 +0100 (Sat, 22 Mar 2008) | 4 lines Small fix that complicated the test actually when that test failed. ................ r61732 | alexandre.vassalotti | 2008-03-22 05:08:44 +0100 (Sat, 22 Mar 2008) | 2 lines Added warning for the removal of 'hotshot' in Py3k. ................ r61733 | georg.brandl | 2008-03-22 11:07:29 +0100 (Sat, 22 Mar 2008) | 4 lines #1918: document that weak references *to* an object are cleared before the object's __del__ is called, to ensure that the weak reference callback (if any) finds the object healthy. ................ r61734 | georg.brandl | 2008-03-22 11:56:23 +0100 (Sat, 22 Mar 2008) | 2 lines Activate the Sphinx doctest extension and convert howto/functional to use it. ................ r61735 | georg.brandl | 2008-03-22 11:58:38 +0100 (Sat, 22 Mar 2008) | 2 lines Allow giving source names on the cmdline. ................ r61737 | georg.brandl | 2008-03-22 12:00:48 +0100 (Sat, 22 Mar 2008) | 2 lines Fixup this HOWTO's doctest blocks so that they can be run with sphinx' doctest builder. ................ r61739 | georg.brandl | 2008-03-22 12:47:10 +0100 (Sat, 22 Mar 2008) | 2 lines Test decimal.rst doctests as far as possible with sphinx doctest. ................ r61741 | georg.brandl | 2008-03-22 13:04:26 +0100 (Sat, 22 Mar 2008) | 2 lines Make doctests in re docs usable with sphinx' doctest. ................ r61743 | georg.brandl | 2008-03-22 13:59:37 +0100 (Sat, 22 Mar 2008) | 2 lines Make more doctests in pprint docs testable. ................ r61744 | georg.brandl | 2008-03-22 14:07:06 +0100 (Sat, 22 Mar 2008) | 2 lines No need to specify explicit "doctest_block" anymore. ................ r61753 | georg.brandl | 2008-03-22 21:08:43 +0100 (Sat, 22 Mar 2008) | 2 lines Fix-up syntax problems. ................ r61761 | georg.brandl | 2008-03-22 22:06:20 +0100 (Sat, 22 Mar 2008) | 4 lines Make collections' doctests executable. (The <BLANKLINE>s will be stripped from presentation output.) ................ r61765 | georg.brandl | 2008-03-22 22:21:57 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in datetime docs. ................ r61766 | georg.brandl | 2008-03-22 22:26:44 +0100 (Sat, 22 Mar 2008) | 2 lines Test doctests in operator docs. ................ r61767 | georg.brandl | 2008-03-22 22:38:33 +0100 (Sat, 22 Mar 2008) | 2 lines Enable doctests in functions.rst. Already found two errors :) ................ r61769 | georg.brandl | 2008-03-22 23:04:10 +0100 (Sat, 22 Mar 2008) | 3 lines Enable doctest running for several other documents. We have now over 640 doctests that are run with "make doctest". ................ r61773 | raymond.hettinger | 2008-03-23 01:55:46 +0100 (Sun, 23 Mar 2008) | 1 line Simplify demo code. ................ r61776 | neal.norwitz | 2008-03-23 04:43:33 +0100 (Sun, 23 Mar 2008) | 7 lines Try to make this test a little more robust and not fail with: timeout (10.0025) is more than 2 seconds more than expected (0.001) I'm assuming this problem is caused by DNS lookup. This change does a DNS lookup of the hostname before trying to connect, so the time is not included. ................ r61777 | neal.norwitz | 2008-03-23 05:08:30 +0100 (Sun, 23 Mar 2008) | 1 line Speed up the test by avoiding socket timeouts. ................ r61778 | neal.norwitz | 2008-03-23 05:43:09 +0100 (Sun, 23 Mar 2008) | 1 line Skip the epoll test if epoll() does not work ................ r61780 | neal.norwitz | 2008-03-23 06:47:20 +0100 (Sun, 23 Mar 2008) | 1 line Suppress failure (to avoid a flaky test) if we cannot connect to svn.python.org ................ r61781 | neal.norwitz | 2008-03-23 07:13:25 +0100 (Sun, 23 Mar 2008) | 4 lines Move itertools before future_builtins since the latter depends on the former. From a clean build importing future_builtins would fail since itertools wasn't built yet. ................ r61782 | neal.norwitz | 2008-03-23 07:16:04 +0100 (Sun, 23 Mar 2008) | 1 line Try to prevent the alarm going off early in tearDown ................ r61783 | neal.norwitz | 2008-03-23 07:19:57 +0100 (Sun, 23 Mar 2008) | 4 lines Remove compiler warnings (on Alpha at least) about using chars as array subscripts. Using chars are dangerous b/c they are signed on some platforms and unsigned on others. ................ r61788 | georg.brandl | 2008-03-23 09:05:30 +0100 (Sun, 23 Mar 2008) | 2 lines Make the doctests presentation-friendlier. ................ r61793 | amaury.forgeotdarc | 2008-03-23 10:55:29 +0100 (Sun, 23 Mar 2008) | 4 lines #1477: ur'\U0010FFFF' raised in narrow unicode builds. Corrected the raw-unicode-escape codec to use UTF-16 surrogates in this case, just like the unicode-escape codec. ................ r61796 | raymond.hettinger | 2008-03-23 14:32:32 +0100 (Sun, 23 Mar 2008) | 1 line Issue 1681432: Add triangular distribution the random module. ................ r61807 | raymond.hettinger | 2008-03-23 20:37:53 +0100 (Sun, 23 Mar 2008) | 4 lines Adopt Nick's suggestion for useful default arguments. Clean-up floating point issues by adding true division and float constants. ................ r61813 | gregory.p.smith | 2008-03-23 22:04:43 +0100 (Sun, 23 Mar 2008) | 6 lines Fix gzip to deal with CRC's being signed values in Python 2.x properly and to read 32bit values as unsigned to start with rather than applying signedness fixups allover the place afterwards. This hopefully fixes the test_tarfile failure on the alpha/tru64 buildbot. ................
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.. function:: betavariate(alpha, beta)
Beta distribution. Conditions on the parameters are ``alpha > 0`` and ``beta >
0``. Returned values range between 0 and 1.
.. function:: expovariate(lambd)
Exponential distribution. *lambd* is 1.0 divided by the desired mean. (The
parameter would be called "lambda", but that is a reserved word in Python.)
Returned values range from 0 to positive infinity.
.. function:: gammavariate(alpha, beta)
Gamma distribution. (*Not* the gamma function!) Conditions on the parameters
are ``alpha > 0`` and ``beta > 0``.
.. function:: gauss(mu, sigma)
Gaussian distribution. *mu* is the mean, and *sigma* is the standard deviation.
This is slightly faster than the :func:`normalvariate` function defined below.
.. function:: lognormvariate(mu, sigma)
Log normal distribution. If you take the natural logarithm of this
distribution, you'll get a normal distribution with mean *mu* and standard
deviation *sigma*. *mu* can have any value, and *sigma* must be greater than
zero.
.. function:: normalvariate(mu, sigma)
Normal distribution. *mu* is the mean, and *sigma* is the standard deviation.
.. function:: vonmisesvariate(mu, kappa)
*mu* is the mean angle, expressed in radians between 0 and 2\*\ *pi*, and *kappa*
is the concentration parameter, which must be greater than or equal to zero. If
*kappa* is equal to zero, this distribution reduces to a uniform random angle
over the range 0 to 2\*\ *pi*.
.. function:: paretovariate(alpha)
Pareto distribution. *alpha* is the shape parameter.
.. function:: weibullvariate(alpha, beta)
Weibull distribution. *alpha* is the scale parameter and *beta* is the shape
parameter.
Alternative Generators:
.. 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,
the :meth:`seed` and :meth:`jumpahead` methods have no effect and are 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
equidistributed uniform pseudorandom number generator", ACM Transactions on
Modeling and Computer Simulation Vol. 8, No. 1, January pp.3-30 1998.