python模块：random

 """Random variable generators.

     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.

 """

 from warnings import warn as _warn
 from types import MethodType as _MethodType, BuiltinMethodType as _BuiltinMethodType
 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 os import urandom as _urandom
 from _collections_abc import Set as _Set, Sequence as _Sequence
 from hashlib import sha512 as _sha512
 import itertools as _itertools
 import bisect as _bisect

 __all__ = ["Random","seed","random","uniform","randint","choice","sample",
            "randrange","shuffle","normalvariate","lognormvariate",
            "expovariate","vonmisesvariate","gammavariate","triangular",
            "gauss","betavariate","paretovariate","weibullvariate",
            "getstate","setstate", "getrandbits", "choices",
            "SystemRandom"]

 NV_MAGICCONST = 4 * _exp(-0.5)/_sqrt(2.0)
 TWOPI = 2.0*_pi
 LOG4 = _log(4.0)
 SG_MAGICCONST = 1.0 + _log(4.5)
 BPF = 53        # Number of bits in a float
 RECIP_BPF = 2**-BPF

 # 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.

 import _random

 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 hashable object.

         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)):
             x = ord(a[0]) << 7 if a else 0
             for c in a:
                 x = ((1000003 * x) ^ ord(c)) & 0xFFFFFFFFFFFFFFFF
             x ^= len(a)
             a = -2 if x == -1 else x

         if version == 2 and isinstance(a, (str, bytes, bytearray)):
             if isinstance(a, str):
                 a = a.encode()
             a += _sha512(a).digest()
             a = int.from_bytes(a, 'big')

         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 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()

 ## -------------------- integer methods  -------------------

     def randrange(self, start, stop=None, step=1, _int=int):
         """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)

     def _randbelow(self, n, int=int, maxsize=1<<BPF, type=type,
                    Method=_MethodType, BuiltinMethod=_BuiltinMethodType):
         "Return a random int in the range [0,n).  Raises ValueError if n==0."

         random = self.random
         getrandbits = self.getrandbits
         # Only call self.getrandbits if the original random() builtin method
         # has not been overridden or if a new getrandbits() was supplied.
         if type(random) is BuiltinMethod or type(getrandbits) is Method:
             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
         # There's an overridden random() method but no new getrandbits() method,
         # so we can only use random() from here.
         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 int(random() * n)
         rem = maxsize % n
         limit = (maxsize - rem) / maxsize   # int(limit * maxsize) % n == 0
         r = random()
         while r >= limit:
             r = random()
         return int(r*maxsize) % n

 ## -------------------- sequence methods  -------------------

     def choice(self, seq):
         """Choose a random element from a non-empty sequence."""
         try:
             i = self._randbelow(len(seq))
         except ValueError:
             raise IndexError('Cannot choose from an empty sequence') from None
         return seq[i]

     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:
             _int = int
             for i in reversed(range(1, len(x))):
                 # pick an element in x[:i+1] with which to exchange x[i]
                 j = _int(random() * (i+1))
                 x[i], x[j] = x[j], x[i]

     def sample(self, population, k):
         """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.

         To choose a sample in a range of integers, use range as an 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.

         if isinstance(population, _Set):
             population = tuple(population)
         if not isinstance(population, _Sequence):
             raise TypeError("Population must be a sequence or set.  For dicts, use list(d).")
         randbelow = self._randbelow
         n = len(population)
         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
             pool = list(population)
             for i in range(k):         # invariant:  non-selected at [0,n-i)
                 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
         if cum_weights is None:
             if weights is None:
                 _int = int
                 total = len(population)
                 return [population[_int(random() * total)] for i in range(k)]
             cum_weights = list(_itertools.accumulate(weights))
         elif weights is not None:
             raise TypeError('Cannot specify both weights and cumulative weights')
         if len(cum_weights) != len(population):
             raise ValueError('The number of weights does not match the population')
         bisect = _bisect.bisect
         total = cum_weights[-1]
         return [population[bisect(cum_weights, random() * total)] for i in range(k)]

 ## -------------------- real-valued distributions  -------------------

 ## -------------------- uniform distribution -------------------

     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()

 ## -------------------- triangular --------------------

     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) * (u * c) ** 0.5

 ## -------------------- normal distribution --------------------

     def normalvariate(self, mu, sigma):
         """Normal distribution.

         mu is the mean, and sigma is the standard deviation.

         """
         # mu = mean, sigma = 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 1:
             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

 ## -------------------- lognormal distribution --------------------

     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))

 ## -------------------- exponential distribution --------------------

     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

 ## -------------------- von Mises distribution --------------------

     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.

         """
         # mu:    mean angle (in radians between 0 and 2*pi)
         # kappa: concentration parameter kappa (>= 0)
         # if kappa = 0 generate uniform random angle

         # 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 1:
             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

 ## -------------------- gamma distribution --------------------

     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 < .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)
             u = random()
             while u <= 1e-7:
                 u = random()
             return -_log(u) * beta

         else:   # alpha is between 0 and 1 (exclusive)

             # Uses ALGORITHM GS of Statistical Computing - Kennedy & Gentle

             while 1:
                 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

 ## -------------------- Gauss (faster alternative) --------------------

     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

 ## -------------------- beta --------------------
 ## 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.

     def betavariate(self, alpha, beta):
         """Beta distribution.

         Conditions on the parameters are alpha > 0 and beta > 0.
         Returned values range between 0 and 1.

         """

         # 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 == 0:
             return 0.0
         else:
             return y / (y + self.gammavariate(beta, 1.0))

 ## -------------------- Pareto --------------------

     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)

 ## -------------------- Weibull --------------------

     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 greater than zero')
         if k != int(k):
             raise TypeError('number of bits should be an integer')
         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 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

 ## -------------------- test program --------------------

 def _test_generator(n, func, args):
     import time
     print(n, 'times', func.__name__)
     total = 0.0
     sqsum = 0.0
     smallest = 1e10
     largest = -1e10
     t0 = time.time()
     for i in range(n):
         x = func(*args)
         total += x
         sqsum = sqsum + x*x
         smallest = min(x, smallest)
         largest = max(x, largest)
     t1 = time.time()
     print(round(t1-t0, 3), 'sec,', end=' ')
     avg = total/n
     stddev = _sqrt(sqsum/n - avg*avg)
     print('avg %g, stddev %g, min %g, max %g\n' % \
               (avg, stddev, smallest, largest))

 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))

 # 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

 if __name__ == '__main__':
     _test()

python:random