python random库的用法简析
我们在密码学中提到过随机数和伪随机数发生器的概念。
随机数在公钥密码*中有着广泛的应用。例如使用随机数作为公钥密码算法中的密钥，RSA加密和数字签名的素数，DES的密钥等。
random模块为我们提供了一个方便且快速的伪随机数发生器。
先把英文文档贴在这里。
点击查看代码
Help on module random:
NAME
random - Random variable generators.
MODULE REFERENCE
https://docs.python.org/3.8/library/random
The following documentation is automatically generated from the Python
source files. It may be incomplete, incorrect or include features that
are considered implementation detail and may vary between Python
implementations. When in doubt, consult the module reference at the
location listed above.
DESCRIPTION
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.
CLASSES
_random.Random(builtins.object)
Random
SystemRandom
class Random(_random.Random)
| Random(x=None)
|
| 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.
|
| Method resolution order:
| Random
| _random.Random
| builtins.object
|
| Methods defined here:
|
| __getstate__(self)
| # 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.
|
| __init__(self, x=None)
| Initialize an instance.
|
| Optional argument x controls seeding, as for Random.seed().
|
| __reduce__(self)
| Helper for pickle.
|
| __setstate__(self, state)
|
| betavariate(self, alpha, beta)
| Beta distribution.
|
| Conditions on the parameters are alpha > 0 and beta > 0.
| Returned values range between 0 and 1.
|
| choice(self, seq)
| Choose a random element from a non-empty sequence.
|
| 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.
|
| 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.
|
| 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
|
| 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.
|
| getstate(self)
| Return internal state; can be passed to setstate() later.
|
| 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.
|
| normalvariate(self, mu, sigma)
| Normal distribution.
|
| mu is the mean, and sigma is the standard deviation.
|
| paretovariate(self, alpha)
| Pareto distribution. alpha is the shape parameter.
|
| randint(self, a, b)
| Return random integer in range [a, b], including both end points.
|
| randrange(self, start, stop=None, step=1, _int=<class ‘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.
|
| 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)
|
| 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.
|
| setstate(self, state)
| Restore internal state from object returned by getstate().
|
| 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.
|
| 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
|
| uniform(self, a, b)
| Get a random number in the range [a, b) or [a, b] depending on rounding.
|
| 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.
|
| weibullvariate(self, alpha, beta)
| Weibull distribution.
|
| alpha is the scale parameter and beta is the shape parameter.
|
| ----------------------------------------------------------------------
| Class methods defined here:
|
| __init_subclass__(**kwargs) from builtins.type
| 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.
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| VERSION = 3
|
| ----------------------------------------------------------------------
| Methods inherited from _random.Random:
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| getrandbits(self, k, /)
| getrandbits(k) -> x. Generates an int with k random bits.
|
| random(self, /)
| random() -> x in the interval [0, 1).
|
| ----------------------------------------------------------------------
| Static methods inherited from _random.Random:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
class SystemRandom(Random)
| SystemRandom(x=None)
|
| 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).
|
| Method resolution order:
| SystemRandom
| Random
| _random.Random
| builtins.object
|
| Methods defined here:
|
| getrandbits(self, k)
| getrandbits(k) -> x. Generates an int with k random bits.
|
| getstate = _notimplemented(self, *args, **kwds)
|
| random(self)
| Get the next random number in the range [0.0, 1.0).
|
| seed(self, *args, **kwds)
| Stub method. Not used for a system random number generator.
|
| setstate = _notimplemented(self, *args, **kwds)
|
| ----------------------------------------------------------------------
| Methods inherited from Random:
|
| __getstate__(self)
| # 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.
|
| __init__(self, x=None)
| Initialize an instance.
|
| Optional argument x controls seeding, as for Random.seed().
|
| __reduce__(self)
| Helper for pickle.
|
| __setstate__(self, state)
|
| betavariate(self, alpha, beta)
| Beta distribution.
|
| Conditions on the parameters are alpha > 0 and beta > 0.
| Returned values range between 0 and 1.
|
| choice(self, seq)
| Choose a random element from a non-empty sequence.
|
| 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.
|
| 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.
|
| 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
|
| 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.
|
| 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.
|
| normalvariate(self, mu, sigma)
| Normal distribution.
|
| mu is the mean, and sigma is the standard deviation.
|
| paretovariate(self, alpha)
| Pareto distribution. alpha is the shape parameter.
|
| randint(self, a, b)
| Return random integer in range [a, b], including both end points.
|
| randrange(self, start, stop=None, step=1, _int=<class ‘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.
|
| 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)
|
| 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.
|
| 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
|
| uniform(self, a, b)
| Get a random number in the range [a, b) or [a, b] depending on rounding.
|
| 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.
|
| weibullvariate(self, alpha, beta)
| Weibull distribution.
|
| alpha is the scale parameter and beta is the shape parameter.
|
| ----------------------------------------------------------------------
| Class methods inherited from Random:
|
| __init_subclass__(**kwargs) from builtins.type
| 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.
|
| ----------------------------------------------------------------------
| Data descriptors inherited from Random:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from Random:
|
| VERSION = 3
|
| ----------------------------------------------------------------------
| Methods inherited from _random.Random:
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| ----------------------------------------------------------------------
| Static methods inherited from _random.Random:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
FUNCTIONS
betavariate(alpha, beta) method of Random instance
Beta distribution.
Conditions on the parameters are alpha > 0 and beta > 0.
Returned values range between 0 and 1.
choice(seq) method of Random instance
Choose a random element from a non-empty sequence.
choices(population, weights=None, *, cum_weights=None, k=1) method of Random instance
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.
expovariate(lambd) method of Random instance
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.
gammavariate(alpha, beta) method of Random instance
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
gauss(mu, sigma) method of Random instance
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.
getrandbits(k, /) method of Random instance
getrandbits(k) -> x. Generates an int with k random bits.
getstate() method of Random instance
Return internal state; can be passed to setstate() later.
lognormvariate(mu, sigma) method of Random instance
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.
normalvariate(mu, sigma) method of Random instance
Normal distribution.
mu is the mean, and sigma is the standard deviation.
paretovariate(alpha) method of Random instance
Pareto distribution. alpha is the shape parameter.
randint(a, b) method of Random instance
Return random integer in range [a, b], including both end points.
random() method of Random instance
random() -> x in the interval [0, 1).
randrange(start, stop=None, step=1, _int=<class ‘int‘>) method of Random instance
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.
sample(population, k) method of Random instance
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)
seed(a=None, version=2) method of Random instance
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.
setstate(state) method of Random instance
Restore internal state from object returned by getstate().
shuffle(x, random=None) method of Random instance
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.
triangular(low=0.0, high=1.0, mode=None) method of Random instance
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
uniform(a, b) method of Random instance
Get a random number in the range [a, b) or [a, b] depending on rounding.
vonmisesvariate(mu, kappa) method of Random instance
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.
weibullvariate(alpha, beta) method of Random instance
Weibull distribution.
alpha is the scale parameter and beta is the shape parameter.
DATA
__all__ = [‘Random‘, ‘seed‘, ‘random‘, ‘uniform‘, ‘randint‘, ‘choice‘,...
FILE
d:\anaconda3\lib\random.py1.random函数
返回一个落在[0,1)范围内的随机浮点值。
2.uniform函数
返回指定区间[a,b]内的一个随机值。
3.randint函数
返回闭区间[a,b]的一个随机整数值。
4.randrange函数
除了开始值和结束值，还有一个步长值。等价于从range(start，stop，step)中选择一个随机值返回。
该函数更加高效，因为它没有真正构造一个区间。
点击查看代码
for i in range(5):
x=rd.random()
print(x)
‘‘‘
0.6330991939020664
0.8830984197895451
0.8244798733795524
0.7175085341098889
0.010479617950157616
‘‘‘
for i in range(5):
x=rd.uniform(5,10)
print(x)
‘‘‘
5.123263387529127
9.971978038032656
9.26300088246108
7.740537789455242
8.84881415728859
‘‘‘
for x in range(5):
print(rd.randint(1,100),end=‘ ‘)
‘‘‘
for x in range(5):
print(rd.randint(1,100),end=‘ ‘)
‘‘‘
for x in range(5):
print(rd.randrange(0,100,5),end=‘ ‘)
‘‘‘
10 5 95 5 25
‘‘‘
5.随机选择元素
rd.choice()函数，从一个类数组序列中随机选择元素
点击查看代码
#一个简单的抛硬币程序
A={‘a‘:0,‘b‘:0}
B=[‘a‘,‘b‘]
for x in range(50000):
A[rd.choice(B)]+=1
print(A)
‘‘‘
{‘a‘: 24799, ‘b‘: 25201}
‘‘‘6.排列
rd.shuffle()函数，返回一个可变类型的全排列。
点击查看代码
A=list(range(16))
for i in range(4):
rd.shuffle(A)
print(A)
‘‘‘
[13, 14, 1, 2, 10, 9, 0, 8, 5, 15, 12, 3, 4, 7, 6, 11]
[9, 11, 2, 7, 14, 1, 15, 6, 5, 13, 0, 8, 12, 4, 3, 10]
[4, 10, 1, 5, 7, 15, 9, 0, 2, 3, 14, 6, 8, 13, 11, 12]
[11, 13, 7, 0, 14, 10, 2, 12, 8, 5, 4, 6, 15, 3, 9, 1]
‘‘‘7.采样
rd.sample()函数，从输入数据中返回一个随机无重复值样本，且不会修改输入序列。
点击查看代码
with open(r‘C:\Users\zzy\PycharmProjects\pythonProject\x.txt‘,‘rt‘) as f:
words=f.readlines()
words=[w.rstrip() for w in words]
print(rd.sample(words,5))
‘‘‘
[‘smile‘, ‘cat‘, ‘say‘, ‘apple‘, ‘dragon‘]
‘‘‘
x=rd.sample(range(1000),50)
print(x)
‘‘‘
[936, 233, 607, 837, 606, 408, 566, 2, 383, 222, 774, 578, 554, 820, 811, 74, 253, 43, 911, 592, 322, 906, 626, 641, 609, 428, 75, 601, 378, 102, 882, 555, 523, 41, 977, 827, 677, 119, 628, 573, 965, 652, 236, 14, 510, 672, 973, 591, 347, 670]
‘‘‘8.种子
rd.seed()函数，用来初始化伪随机数发生器，因为公式是确定的，产生的序列也将是确定的。
点击查看代码
for x in range(10):#重复十次
rd.seed(5)#设定种子
print(rd.random())
‘‘‘
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
0.6229016948897019
‘‘‘
for x in range(3):#重复三次
rd.seed(5)#设定种子
for i in range(5):#生成五个随机值
print(‘{:4.3f}‘.format(rd.random()),end=‘ ‘)
print(‘\n‘)
‘‘‘
0.623 0.742 0.795 0.942 0.740
0.623 0.742 0.795 0.942 0.740
0.623 0.742 0.795 0.942 0.740
‘‘‘
def fun(n,s=5):
rd.seed(s)
x=[]
for i in range(n):
x.append(rd.randint(1,1000))
return x
print(fun(10,5))
print(fun(10,5))
a=fun(10000,5)
b=fun(10000,5)
print(a == b)
‘‘‘
[638, 262, 760, 368, 815, 708, 966, 862, 758, 668]
[638, 262, 760, 368, 815, 708, 966, 862, 758, 668]
True
‘‘‘
#可以看出，这个伪随机数发生器的周期是非常大的