|
"""Random variable generators. |
|
|
|
bytes |
|
----- |
|
uniform bytes (values between 0 and 255) |
|
|
|
integers |
|
-------- |
|
uniform within range |
|
|
|
sequences |
|
--------- |
|
pick random element |
|
pick random sample |
|
pick weighted random sample |
|
generate random permutation |
|
|
|
distributions on the real line: |
|
------------------------------ |
|
uniform |
|
triangular |
|
normal (Gaussian) |
|
lognormal |
|
negative exponential |
|
gamma |
|
beta |
|
pareto |
|
Weibull |
|
|
|
distributions on the circle (angles 0 to 2pi) |
|
--------------------------------------------- |
|
circular uniform |
|
von Mises |
|
|
|
General notes on the underlying Mersenne Twister core generator: |
|
|
|
* The period is 2**19937-1. |
|
* It is one of the most extensively tested generators in existence. |
|
* The random() method is implemented in C, executes in a single Python step, |
|
and is, therefore, threadsafe. |
|
|
|
""" |
|
|
|
# Translated by Guido van Rossum from C source provided by |
|
# Adrian Baddeley. Adapted by Raymond Hettinger for use with |
|
# the Mersenne Twister and os.urandom() core generators. |
|
|
|
from warnings import warn as _warn |
|
from math import log as _log, exp as _exp, pi as _pi, e as _e, ceil as _ceil |
|
from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin |
|
from math import tau as TWOPI, floor as _floor |
|
from os import urandom as _urandom |
|
from _collections_abc import Set as _Set, Sequence as _Sequence |
|
from itertools import accumulate as _accumulate, repeat as _repeat |
|
from bisect import bisect as _bisect |
|
import os as _os |
|
import _random |
|
|
|
try: |
|
# hashlib is pretty heavy to load, try lean internal module first |
|
from _sha512 import sha512 as _sha512 |
|
except ImportError: |
|
# fallback to official implementation |
|
from hashlib import sha512 as _sha512 |
|
|
|
__all__ = [ |
|
"Random", |
|
"SystemRandom", |
|
"betavariate", |
|
"choice", |
|
"choices", |
|
"expovariate", |
|
"gammavariate", |
|
"gauss", |
|
"getrandbits", |
|
"getstate", |
|
"lognormvariate", |
|
"normalvariate", |
|
"paretovariate", |
|
"randbytes", |
|
"randint", |
|
"random", |
|
"randrange", |
|
"sample", |
|
"seed", |
|
"setstate", |
|
"shuffle", |
|
"triangular", |
|
"uniform", |
|
"vonmisesvariate", |
|
"weibullvariate", |
|
] |
|
|
|
NV_MAGICCONST = 4 * _exp(-0.5) / _sqrt(2.0) |
|
LOG4 = _log(4.0) |
|
SG_MAGICCONST = 1.0 + _log(4.5) |
|
BPF = 53 # Number of bits in a float |
|
RECIP_BPF = 2 ** -BPF |
|
|
|
|
|
class Random(_random.Random): |
|
"""Random number generator base class used by bound module functions. |
|
|
|
Used to instantiate instances of Random to get generators that don't |
|
share state. |
|
|
|
Class Random can also be subclassed if you want to use a different basic |
|
generator of your own devising: in that case, override the following |
|
methods: random(), seed(), getstate(), and setstate(). |
|
Optionally, implement a getrandbits() method so that randrange() |
|
can cover arbitrarily large ranges. |
|
|
|
""" |
|
|
|
VERSION = 3 # used by getstate/setstate |
|
|
|
def __init__(self, x=None): |
|
"""Initialize an instance. |
|
|
|
Optional argument x controls seeding, as for Random.seed(). |
|
""" |
|
|
|
self.seed(x) |
|
self.gauss_next = None |
|
|
|
def seed(self, a=None, version=2): |
|
"""Initialize internal state from a seed. |
|
|
|
The only supported seed types are None, int, float, |
|
str, bytes, and bytearray. |
|
|
|
None or no argument seeds from current time or from an operating |
|
system specific randomness source if available. |
|
|
|
If *a* is an int, all bits are used. |
|
|
|
For version 2 (the default), all of the bits are used if *a* is a str, |
|
bytes, or bytearray. For version 1 (provided for reproducing random |
|
sequences from older versions of Python), the algorithm for str and |
|
bytes generates a narrower range of seeds. |
|
|
|
""" |
|
|
|
if version == 1 and isinstance(a, (str, bytes)): |
|
a = a.decode('latin-1') if isinstance(a, bytes) else a |
|
x = ord(a[0]) << 7 if a else 0 |
|
for c in map(ord, a): |
|
x = ((1000003 * x) ^ c) & 0xFFFFFFFFFFFFFFFF |
|
x ^= len(a) |
|
a = -2 if x == -1 else x |
|
|
|
elif version == 2 and isinstance(a, (str, bytes, bytearray)): |
|
if isinstance(a, str): |
|
a = a.encode() |
|
a = int.from_bytes(a + _sha512(a).digest(), 'big') |
|
|
|
elif not isinstance(a, (type(None), int, float, str, bytes, bytearray)): |
|
_warn('Seeding based on hashing is deprecated\n' |
|
'since Python 3.9 and will be removed in a subsequent ' |
|
'version. The only \n' |
|
'supported seed types are: None, ' |
|
'int, float, str, bytes, and bytearray.', |
|
DeprecationWarning, 2) |
|
|
|
super().seed(a) |
|
self.gauss_next = None |
|
|
|
def getstate(self): |
|
"""Return internal state; can be passed to setstate() later.""" |
|
return self.VERSION, super().getstate(), self.gauss_next |
|
|
|
def setstate(self, state): |
|
"""Restore internal state from object returned by getstate().""" |
|
version = state[0] |
|
if version == 3: |
|
version, internalstate, self.gauss_next = state |
|
super().setstate(internalstate) |
|
elif version == 2: |
|
version, internalstate, self.gauss_next = state |
|
# In version 2, the state was saved as signed ints, which causes |
|
# inconsistencies between 32/64-bit systems. The state is |
|
# really unsigned 32-bit ints, so we convert negative ints from |
|
# version 2 to positive longs for version 3. |
|
try: |
|
internalstate = tuple(x % (2 ** 32) for x in internalstate) |
|
except ValueError as e: |
|
raise TypeError from e |
|
super().setstate(internalstate) |
|
else: |
|
raise ValueError("state with version %s passed to " |
|
"Random.setstate() of version %s" % |
|
(version, self.VERSION)) |
|
|
|
|
|
## ------------------------------------------------------- |
|
## ---- Methods below this point do not need to be overridden or extended |
|
## ---- when subclassing for the purpose of using a different core generator. |
|
|
|
|
|
## -------------------- pickle support ------------------- |
|
|
|
# Issue 17489: Since __reduce__ was defined to fix #759889 this is no |
|
# longer called; we leave it here because it has been here since random was |
|
# rewritten back in 2001 and why risk breaking something. |
|
def __getstate__(self): # for pickle |
|
return self.getstate() |
|
|
|
def __setstate__(self, state): # for pickle |
|
self.setstate(state) |
|
|
|
def __reduce__(self): |
|
return self.__class__, (), self.getstate() |
|
|
|
|
|
## ---- internal support method for evenly distributed integers ---- |
|
|
|
def __init_subclass__(cls, /, **kwargs): |
|
"""Control how subclasses generate random integers. |
|
|
|
The algorithm a subclass can use depends on the random() and/or |
|
getrandbits() implementation available to it and determines |
|
whether it can generate random integers from arbitrarily large |
|
ranges. |
|
""" |
|
|
|
for c in cls.__mro__: |
|
if '_randbelow' in c.__dict__: |
|
# just inherit it |
|
break |
|
if 'getrandbits' in c.__dict__: |
|
cls._randbelow = cls._randbelow_with_getrandbits |
|
break |
|
if 'random' in c.__dict__: |
|
cls._randbelow = cls._randbelow_without_getrandbits |
|
break |
|
|
|
def _randbelow_with_getrandbits(self, n): |
|
"Return a random int in the range [0,n). Returns 0 if n==0." |
|
|
|
if not n: |
|
return 0 |
|
getrandbits = self.getrandbits |
|
k = n.bit_length() # don't use (n-1) here because n can be 1 |
|
r = getrandbits(k) # 0 <= r < 2**k |
|
while r >= n: |
|
r = getrandbits(k) |
|
return r |
|
|
|
def _randbelow_without_getrandbits(self, n, maxsize=1<<BPF): |
|
"""Return a random int in the range [0,n). Returns 0 if n==0. |
|
|
|
The implementation does not use getrandbits, but only random. |
|
""" |
|
|
|
random = self.random |
|
if n >= maxsize: |
|
_warn("Underlying random() generator does not supply \n" |
|
"enough bits to choose from a population range this large.\n" |
|
"To remove the range limitation, add a getrandbits() method.") |
|
return _floor(random() * n) |
|
if n == 0: |
|
return 0 |
|
rem = maxsize % n |
|
limit = (maxsize - rem) / maxsize # int(limit * maxsize) % n == 0 |
|
r = random() |
|
while r >= limit: |
|
r = random() |
|
return _floor(r * maxsize) % n |
|
|
|
_randbelow = _randbelow_with_getrandbits |
|
|
|
|
|
## -------------------------------------------------------- |
|
## ---- Methods below this point generate custom distributions |
|
## ---- based on the methods defined above. They do not |
|
## ---- directly touch the underlying generator and only |
|
## ---- access randomness through the methods: random(), |
|
## ---- getrandbits(), or _randbelow(). |
|
|
|
|
|
## -------------------- bytes methods --------------------- |
|
|
|
def randbytes(self, n): |
|
"""Generate n random bytes.""" |
|
return self.getrandbits(n * 8).to_bytes(n, 'little') |
|
|
|
|
|
## -------------------- integer methods ------------------- |
|
|
|
def randrange(self, start, stop=None, step=1): |
|
"""Choose a random item from range(start, stop[, step]). |
|
|
|
This fixes the problem with randint() which includes the |
|
endpoint; in Python this is usually not what you want. |
|
|
|
""" |
|
|
|
# This code is a bit messy to make it fast for the |
|
# common case while still doing adequate error checking. |
|
istart = int(start) |
|
if istart != start: |
|
raise ValueError("non-integer arg 1 for randrange()") |
|
if stop is None: |
|
if istart > 0: |
|
return self._randbelow(istart) |
|
raise ValueError("empty range for randrange()") |
|
|
|
# stop argument supplied. |
|
istop = int(stop) |
|
if istop != stop: |
|
raise ValueError("non-integer stop for randrange()") |
|
width = istop - istart |
|
if step == 1 and width > 0: |
|
return istart + self._randbelow(width) |
|
if step == 1: |
|
raise ValueError("empty range for randrange() (%d, %d, %d)" % (istart, istop, width)) |
|
|
|
# Non-unit step argument supplied. |
|
istep = int(step) |
|
if istep != step: |
|
raise ValueError("non-integer step for randrange()") |
|
if istep > 0: |
|
n = (width + istep - 1) // istep |
|
elif istep < 0: |
|
n = (width + istep + 1) // istep |
|
else: |
|
raise ValueError("zero step for randrange()") |
|
|
|
if n <= 0: |
|
raise ValueError("empty range for randrange()") |
|
|
|
return istart + istep * self._randbelow(n) |
|
|
|
def randint(self, a, b): |
|
"""Return random integer in range [a, b], including both end points. |
|
""" |
|
|
|
return self.randrange(a, b+1) |
|
|
|
|
|
## -------------------- sequence methods ------------------- |
|
|
|
def choice(self, seq): |
|
"""Choose a random element from a non-empty sequence.""" |
|
# raises IndexError if seq is empty |
|
return seq[self._randbelow(len(seq))] |
|
|
|
def shuffle(self, x, random=None): |
|
"""Shuffle list x in place, and return None. |
|
|
|
Optional argument random is a 0-argument function returning a |
|
random float in [0.0, 1.0); if it is the default None, the |
|
standard random.random will be used. |
|
|
|
""" |
|
|
|
if random is None: |
|
randbelow = self._randbelow |
|
for i in reversed(range(1, len(x))): |
|
# pick an element in x[:i+1] with which to exchange x[i] |
|
j = randbelow(i + 1) |
|
x[i], x[j] = x[j], x[i] |
|
else: |
|
_warn('The *random* parameter to shuffle() has been deprecated\n' |
|
'since Python 3.9 and will be removed in a subsequent ' |
|
'version.', |
|
DeprecationWarning, 2) |
|
floor = _floor |
|
for i in reversed(range(1, len(x))): |
|
# pick an element in x[:i+1] with which to exchange x[i] |
|
j = floor(random() * (i + 1)) |
|
x[i], x[j] = x[j], x[i] |
|
|
|
def sample(self, population, k, *, counts=None): |
|
"""Chooses k unique random elements from a population sequence or set. |
|
|
|
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). |
|
|
|
Members of the population need not be hashable or unique. If the |
|
population contains repeats, then each occurrence is a possible |
|
selection in the sample. |
|
|
|
Repeated elements can be specified one at a time or with the optional |
|
counts parameter. For example: |
|
|
|
sample(['red', 'blue'], counts=[4, 2], k=5) |
|
|
|
is equivalent to: |
|
|
|
sample(['red', 'red', 'red', 'red', 'blue', 'blue'], k=5) |
|
|
|
To choose a sample from a range of integers, use range() for the |
|
population argument. This is especially fast and space efficient |
|
for sampling from a large population: |
|
|
|
sample(range(10000000), 60) |
|
|
|
""" |
|
|
|
# Sampling without replacement entails tracking either potential |
|
# selections (the pool) in a list or previous selections in a set. |
|
|
|
# When the number of selections is small compared to the |
|
# population, then tracking selections is efficient, requiring |
|
# only a small set and an occasional reselection. For |
|
# a larger number of selections, the pool tracking method is |
|
# preferred since the list takes less space than the |
|
# set and it doesn't suffer from frequent reselections. |
|
|
|
# The number of calls to _randbelow() is kept at or near k, the |
|
# theoretical minimum. This is important because running time |
|
# is dominated by _randbelow() and because it extracts the |
|
# least entropy from the underlying random number generators. |
|
|
|
# Memory requirements are kept to the smaller of a k-length |
|
# set or an n-length list. |
|
|
|
# There are other sampling algorithms that do not require |
|
# auxiliary memory, but they were rejected because they made |
|
# too many calls to _randbelow(), making them slower and |
|
# causing them to eat more entropy than necessary. |
|
|
|
if isinstance(population, _Set): |
|
_warn('Sampling from a set deprecated\n' |
|
'since Python 3.9 and will be removed in a subsequent version.', |
|
DeprecationWarning, 2) |
|
population = tuple(population) |
|
if not isinstance(population, _Sequence): |
|
raise TypeError("Population must be a sequence. For dicts or sets, use sorted(d).") |
|
n = len(population) |
|
if counts is not None: |
|
cum_counts = list(_accumulate(counts)) |
|
if len(cum_counts) != n: |
|
raise ValueError('The number of counts does not match the population') |
|
total = cum_counts.pop() |
|
if not isinstance(total, int): |
|
raise TypeError('Counts must be integers') |
|
if total <= 0: |
|
raise ValueError('Total of counts must be greater than zero') |
|
selections = self.sample(range(total), k=k) |
|
bisect = _bisect |
|
return [population[bisect(cum_counts, s)] for s in selections] |
|
randbelow = self._randbelow |
|
if not 0 <= k <= n: |
|
raise ValueError("Sample larger than population or is negative") |
|
result = [None] * k |
|
setsize = 21 # size of a small set minus size of an empty list |
|
if k > 5: |
|
setsize += 4 ** _ceil(_log(k * 3, 4)) # table size for big sets |
|
if n <= setsize: |
|
# An n-length list is smaller than a k-length set. |
|
# Invariant: non-selected at pool[0 : n-i] |
|
pool = list(population) |
|
for i in range(k): |
|
j = randbelow(n - i) |
|
result[i] = pool[j] |
|
pool[j] = pool[n - i - 1] # move non-selected item into vacancy |
|
else: |
|
selected = set() |
|
selected_add = selected.add |
|
for i in range(k): |
|
j = randbelow(n) |
|
while j in selected: |
|
j = randbelow(n) |
|
selected_add(j) |
|
result[i] = population[j] |
|
return result |
|
|
|
def choices(self, population, weights=None, *, cum_weights=None, k=1): |
|
"""Return a k sized list of population elements chosen with replacement. |
|
|
|
If the relative weights or cumulative weights are not specified, |
|
the selections are made with equal probability. |
|
|
|
""" |
|
random = self.random |
|
n = len(population) |
|
if cum_weights is None: |
|
if weights is None: |
|
floor = _floor |
|
n += 0.0 # convert to float for a small speed improvement |
|
return [population[floor(random() * n)] for i in _repeat(None, k)] |
|
try: |
|
cum_weights = list(_accumulate(weights)) |
|
except TypeError: |
|
if not isinstance(weights, int): |
|
raise |
|
k = weights |
|
raise TypeError( |
|
f'The number of choices must be a keyword argument: {k=}' |
|
) from None |
|
elif weights is not None: |
|
raise TypeError('Cannot specify both weights and cumulative weights') |
|
if len(cum_weights) != n: |
|
raise ValueError('The number of weights does not match the population') |
|
total = cum_weights[-1] + 0.0 # convert to float |
|
if total <= 0.0: |
|
raise ValueError('Total of weights must be greater than zero') |
|
bisect = _bisect |
|
hi = n - 1 |
|
return [population[bisect(cum_weights, random() * total, 0, hi)] |
|
for i in _repeat(None, k)] |
|
|
|
|
|
## -------------------- real-valued distributions ------------------- |
|
|
|
def uniform(self, a, b): |
|
"Get a random number in the range [a, b) or [a, b] depending on rounding." |
|
return a + (b - a) * self.random() |
|
|
|
def triangular(self, low=0.0, high=1.0, mode=None): |
|
"""Triangular distribution. |
|
|
|
Continuous distribution bounded by given lower and upper limits, |
|
and having a given mode value in-between. |
|
|
|
http://en.wikipedia.org/wiki/Triangular_distribution |
|
|
|
""" |
|
u = self.random() |
|
try: |
|
c = 0.5 if mode is None else (mode - low) / (high - low) |
|
except ZeroDivisionError: |
|
return low |
|
if u > c: |
|
u = 1.0 - u |
|
c = 1.0 - c |
|
low, high = high, low |
|
return low + (high - low) * _sqrt(u * c) |
|
|
|
def normalvariate(self, mu, sigma): |
|
"""Normal distribution. |
|
|
|
mu is the mean, and sigma is the standard deviation. |
|
|
|
""" |
|
# Uses Kinderman and Monahan method. Reference: Kinderman, |
|
# A.J. and Monahan, J.F., "Computer generation of random |
|
# variables using the ratio of uniform deviates", ACM Trans |
|
# Math Software, 3, (1977), pp257-260. |
|
|
|
random = self.random |
|
while True: |
|
u1 = random() |
|
u2 = 1.0 - random() |
|
z = NV_MAGICCONST * (u1 - 0.5) / u2 |
|
zz = z * z / 4.0 |
|
if zz <= -_log(u2): |
|
break |
|
return mu + z * sigma |
|
|
|
def gauss(self, mu, sigma): |
|
"""Gaussian distribution. |
|
|
|
mu is the mean, and sigma is the standard deviation. This is |
|
slightly faster than the normalvariate() function. |
|
|
|
Not thread-safe without a lock around calls. |
|
|
|
""" |
|
# When x and y are two variables from [0, 1), uniformly |
|
# distributed, then |
|
# |
|
# cos(2*pi*x)*sqrt(-2*log(1-y)) |
|
# sin(2*pi*x)*sqrt(-2*log(1-y)) |
|
# |
|
# are two *independent* variables with normal distribution |
|
# (mu = 0, sigma = 1). |
|
# (Lambert Meertens) |
|
# (corrected version; bug discovered by Mike Miller, fixed by LM) |
|
|
|
# Multithreading note: When two threads call this function |
|
# simultaneously, it is possible that they will receive the |
|
# same return value. The window is very small though. To |
|
# avoid this, you have to use a lock around all calls. (I |
|
# didn't want to slow this down in the serial case by using a |
|
# lock here.) |
|
|
|
random = self.random |
|
z = self.gauss_next |
|
self.gauss_next = None |
|
if z is None: |
|
x2pi = random() * TWOPI |
|
g2rad = _sqrt(-2.0 * _log(1.0 - random())) |
|
z = _cos(x2pi) * g2rad |
|
self.gauss_next = _sin(x2pi) * g2rad |
|
|
|
return mu + z * sigma |
|
|
|
def lognormvariate(self, 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. |
|
|
|
""" |
|
return _exp(self.normalvariate(mu, sigma)) |
|
|
|
def expovariate(self, lambd): |
|
"""Exponential distribution. |
|
|
|
lambd is 1.0 divided by the desired mean. It should be |
|
nonzero. (The parameter would be called "lambda", but that is |
|
a reserved word in Python.) Returned values range from 0 to |
|
positive infinity if lambd is positive, and from negative |
|
infinity to 0 if lambd is negative. |
|
|
|
""" |
|
# lambd: rate lambd = 1/mean |
|
# ('lambda' is a Python reserved word) |
|
|
|
# we use 1-random() instead of random() to preclude the |
|
# possibility of taking the log of zero. |
|
return -_log(1.0 - self.random()) / lambd |
|
|
|
def vonmisesvariate(self, mu, kappa): |
|
"""Circular data distribution. |
|
|
|
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. |
|
|
|
""" |
|
# Based upon an algorithm published in: Fisher, N.I., |
|
# "Statistical Analysis of Circular Data", Cambridge |
|
# University Press, 1993. |
|
|
|
# Thanks to Magnus Kessler for a correction to the |
|
# implementation of step 4. |
|
|
|
random = self.random |
|
if kappa <= 1e-6: |
|
return TWOPI * random() |
|
|
|
s = 0.5 / kappa |
|
r = s + _sqrt(1.0 + s * s) |
|
|
|
while True: |
|
u1 = random() |
|
z = _cos(_pi * u1) |
|
|
|
d = z / (r + z) |
|
u2 = random() |
|
if u2 < 1.0 - d * d or u2 <= (1.0 - d) * _exp(d): |
|
break |
|
|
|
q = 1.0 / r |
|
f = (q + z) / (1.0 + q * z) |
|
u3 = random() |
|
if u3 > 0.5: |
|
theta = (mu + _acos(f)) % TWOPI |
|
else: |
|
theta = (mu - _acos(f)) % TWOPI |
|
|
|
return theta |
|
|
|
def gammavariate(self, alpha, beta): |
|
"""Gamma distribution. Not the gamma function! |
|
|
|
Conditions on the parameters are alpha > 0 and beta > 0. |
|
|
|
The probability distribution function is: |
|
|
|
x ** (alpha - 1) * math.exp(-x / beta) |
|
pdf(x) = -------------------------------------- |
|
math.gamma(alpha) * beta ** alpha |
|
|
|
""" |
|
# alpha > 0, beta > 0, mean is alpha*beta, variance is alpha*beta**2 |
|
|
|
# Warning: a few older sources define the gamma distribution in terms |
|
# of alpha > -1.0 |
|
if alpha <= 0.0 or beta <= 0.0: |
|
raise ValueError('gammavariate: alpha and beta must be > 0.0') |
|
|
|
random = self.random |
|
if alpha > 1.0: |
|
|
|
# Uses R.C.H. Cheng, "The generation of Gamma |
|
# variables with non-integral shape parameters", |
|
# Applied Statistics, (1977), 26, No. 1, p71-74 |
|
|
|
ainv = _sqrt(2.0 * alpha - 1.0) |
|
bbb = alpha - LOG4 |
|
ccc = alpha + ainv |
|
|
|
while 1: |
|
u1 = random() |
|
if not 1e-7 < u1 < 0.9999999: |
|
continue |
|
u2 = 1.0 - random() |
|
v = _log(u1 / (1.0 - u1)) / ainv |
|
x = alpha * _exp(v) |
|
z = u1 * u1 * u2 |
|
r = bbb + ccc * v - x |
|
if r + SG_MAGICCONST - 4.5 * z >= 0.0 or r >= _log(z): |
|
return x * beta |
|
|
|
elif alpha == 1.0: |
|
# expovariate(1/beta) |
|
return -_log(1.0 - random()) * beta |
|
|
|
else: |
|
# alpha is between 0 and 1 (exclusive) |
|
# Uses ALGORITHM GS of Statistical Computing - Kennedy & Gentle |
|
while True: |
|
u = random() |
|
b = (_e + alpha) / _e |
|
p = b * u |
|
if p <= 1.0: |
|
x = p ** (1.0 / alpha) |
|
else: |
|
x = -_log((b - p) / alpha) |
|
u1 = random() |
|
if p > 1.0: |
|
if u1 <= x ** (alpha - 1.0): |
|
break |
|
elif u1 <= _exp(-x): |
|
break |
|
return x * beta |
|
|
|
def betavariate(self, alpha, beta): |
|
"""Beta distribution. |
|
|
|
Conditions on the parameters are alpha > 0 and beta > 0. |
|
Returned values range between 0 and 1. |
|
|
|
""" |
|
## See |
|
## http://mail.python.org/pipermail/python-bugs-list/2001-January/003752.html |
|
## for Ivan Frohne's insightful analysis of why the original implementation: |
|
## |
|
## def betavariate(self, alpha, beta): |
|
## # Discrete Event Simulation in C, pp 87-88. |
|
## |
|
## y = self.expovariate(alpha) |
|
## z = self.expovariate(1.0/beta) |
|
## return z/(y+z) |
|
## |
|
## was dead wrong, and how it probably got that way. |
|
|
|
# This version due to Janne Sinkkonen, and matches all the std |
|
# texts (e.g., Knuth Vol 2 Ed 3 pg 134 "the beta distribution"). |
|
y = self.gammavariate(alpha, 1.0) |
|
if y: |
|
return y / (y + self.gammavariate(beta, 1.0)) |
|
return 0.0 |
|
|
|
def paretovariate(self, alpha): |
|
"""Pareto distribution. alpha is the shape parameter.""" |
|
# Jain, pg. 495 |
|
|
|
u = 1.0 - self.random() |
|
return 1.0 / u ** (1.0 / alpha) |
|
|
|
def weibullvariate(self, alpha, beta): |
|
"""Weibull distribution. |
|
|
|
alpha is the scale parameter and beta is the shape parameter. |
|
|
|
""" |
|
# Jain, pg. 499; bug fix courtesy Bill Arms |
|
|
|
u = 1.0 - self.random() |
|
return alpha * (-_log(u)) ** (1.0 / beta) |
|
|
|
|
|
## ------------------------------------------------------------------ |
|
## --------------- Operating System Random Source ------------------ |
|
|
|
|
|
class SystemRandom(Random): |
|
"""Alternate random number generator using sources provided |
|
by the operating system (such as /dev/urandom on Unix or |
|
CryptGenRandom on Windows). |
|
|
|
Not available on all systems (see os.urandom() for details). |
|
|
|
""" |
|
|
|
def random(self): |
|
"""Get the next random number in the range [0.0, 1.0).""" |
|
return (int.from_bytes(_urandom(7), 'big') >> 3) * RECIP_BPF |
|
|
|
def getrandbits(self, k): |
|
"""getrandbits(k) -> x. Generates an int with k random bits.""" |
|
if k < 0: |
|
raise ValueError('number of bits must be non-negative') |
|
numbytes = (k + 7) // 8 # bits / 8 and rounded up |
|
x = int.from_bytes(_urandom(numbytes), 'big') |
|
return x >> (numbytes * 8 - k) # trim excess bits |
|
|
|
def randbytes(self, n): |
|
"""Generate n random bytes.""" |
|
# os.urandom(n) fails with ValueError for n < 0 |
|
# and returns an empty bytes string for n == 0. |
|
return _urandom(n) |
|
|
|
def seed(self, *args, **kwds): |
|
"Stub method. Not used for a system random number generator." |
|
return None |
|
|
|
def _notimplemented(self, *args, **kwds): |
|
"Method should not be called for a system random number generator." |
|
raise NotImplementedError('System entropy source does not have state.') |
|
getstate = setstate = _notimplemented |
|
|
|
|
|
# ---------------------------------------------------------------------- |
|
# Create one instance, seeded from current time, and export its methods |
|
# as module-level functions. The functions share state across all uses |
|
# (both in the user's code and in the Python libraries), but that's fine |
|
# for most programs and is easier for the casual user than making them |
|
# instantiate their own Random() instance. |
|
|
|
_inst = Random() |
|
seed = _inst.seed |
|
random = _inst.random |
|
uniform = _inst.uniform |
|
triangular = _inst.triangular |
|
randint = _inst.randint |
|
choice = _inst.choice |
|
randrange = _inst.randrange |
|
sample = _inst.sample |
|
shuffle = _inst.shuffle |
|
choices = _inst.choices |
|
normalvariate = _inst.normalvariate |
|
lognormvariate = _inst.lognormvariate |
|
expovariate = _inst.expovariate |
|
vonmisesvariate = _inst.vonmisesvariate |
|
gammavariate = _inst.gammavariate |
|
gauss = _inst.gauss |
|
betavariate = _inst.betavariate |
|
paretovariate = _inst.paretovariate |
|
weibullvariate = _inst.weibullvariate |
|
getstate = _inst.getstate |
|
setstate = _inst.setstate |
|
getrandbits = _inst.getrandbits |
|
randbytes = _inst.randbytes |
|
|
|
|
|
## ------------------------------------------------------ |
|
## ----------------- test program ----------------------- |
|
|
|
def _test_generator(n, func, args): |
|
from statistics import stdev, fmean as mean |
|
from time import perf_counter |
|
|
|
t0 = perf_counter() |
|
data = [func(*args) for i in range(n)] |
|
t1 = perf_counter() |
|
|
|
xbar = mean(data) |
|
sigma = stdev(data, xbar) |
|
low = min(data) |
|
high = max(data) |
|
|
|
print(f'{t1 - t0:.3f} sec, {n} times {func.__name__}') |
|
print('avg %g, stddev %g, min %g, max %g\n' % (xbar, sigma, low, high)) |
|
|
|
|
|
def _test(N=2000): |
|
_test_generator(N, random, ()) |
|
_test_generator(N, normalvariate, (0.0, 1.0)) |
|
_test_generator(N, lognormvariate, (0.0, 1.0)) |
|
_test_generator(N, vonmisesvariate, (0.0, 1.0)) |
|
_test_generator(N, gammavariate, (0.01, 1.0)) |
|
_test_generator(N, gammavariate, (0.1, 1.0)) |
|
_test_generator(N, gammavariate, (0.1, 2.0)) |
|
_test_generator(N, gammavariate, (0.5, 1.0)) |
|
_test_generator(N, gammavariate, (0.9, 1.0)) |
|
_test_generator(N, gammavariate, (1.0, 1.0)) |
|
_test_generator(N, gammavariate, (2.0, 1.0)) |
|
_test_generator(N, gammavariate, (20.0, 1.0)) |
|
_test_generator(N, gammavariate, (200.0, 1.0)) |
|
_test_generator(N, gauss, (0.0, 1.0)) |
|
_test_generator(N, betavariate, (3.0, 3.0)) |
|
_test_generator(N, triangular, (0.0, 1.0, 1.0 / 3.0)) |
|
|
|
|
|
## ------------------------------------------------------ |
|
## ------------------ fork support --------------------- |
|
|
|
if hasattr(_os, "fork"): |
|
_os.register_at_fork(after_in_child=_inst.seed) |
|
|
|
|
|
if __name__ == '__main__': |
|
_test() |