1.4 random模块

Python中的random模块用于生成随机数，下面介绍一下random模块中最常用的几个函数。

国际惯例，用模块之前先导入：

 >>> import random

（一）random.random() ：生成一个0到1的随机符点数: 0 <= n < 1.0，注意范围是包含0不包含1.0的

 >>> random.random()
 0.9860525014920107
 >>> random.random()
 0.022209392510227688
 >>>

（二）random.uniform() ：生成一个指定范围内的随机符点数，两个参数其中一个是上限，一个是下限。如果a > b，则生成的随机数n: a <= n <= b。如果 a <b， 则 b <= n <= a。如果a=b，则生成的随机数n:n=a=b

 >>> random.uniform(1,2)
 1.5701537578549036
 >>> random.uniform(6,7)
 6.328964651708305
 >>> random.uniform(6,6)
 6.0
 >>> random.uniform(7,6)
 6.67299824947645

（三）random.randint(a, b)：生成一个指定范围内的整数。其中参数a是下限，参数b是上限，生成的随机数n: a <= n <= b。如果a>b，会报错。

 >>> random.randint(1,10)
 3
 >>> random.randint(6,6)
 6
 >>> random.randint(8,3)
 Traceback (most recent call last):
   File "<pyshell#13>", line 1, in <module>
     random.randint(8,3)
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 218, in randint
     return self.randrange(a, b+1)
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 196, in randrange
     raise ValueError("empty range for randrange() (%d,%d, %d)" % (istart, istop, width))
 ValueError: empty range for randrange() (8,4, -4)
 >>> 

（四）random.randrange([start], stop[, step])：从指定范围内，按指定基数递增的集合中 获取一个随机数。如：random.randrange(1, 10, 2)，结果相当于从[1, 3, 5, 7, 9]序列中获取一个随机数。random.randrange(1, 10, 2)在结果上与 random.choice(range(1, 10, 2) 等效。

  1 >>> random.randrange(1,10,2)
  2 1
  3 >>> random.randrange(1,10,2)
  4 9
  5 >>> random.randrange(10,1,2)          #表示范围的两个参数必须满足的条件：start < stop
  6 Traceback (most recent call last):
  7   File "<pyshell#19>", line 1, in <module>
  8     random.randrange(10,1,2)
  9   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 210, in randrange
 10     raise ValueError("empty range for randrange()")
 11 ValueError: empty range for randrange()

 12 >>> random.randrange(10,10,2)
 13 Traceback (most recent call last):
 14   File "<pyshell#20>", line 1, in <module>
 15     random.randrange(10,10,2)
 16   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 210, in randrange
 17     raise ValueError("empty range for randrange()")
 18 ValueError: empty range for randrange()

 19 >>> random.randrange(1,2,3)   #如果前两个参数的差值stop - start <= step，则生成的随机数为start
 20 1
 21 >>> random.randrange(1,4,3)
 22 1
 27 >>> random.randrange(1,5,3)
 28 1
 31 >>> random.randrange(1,5,3)
 32 4

 >>> random.randrange(5)             #当传入一个参数时，默认start = 0,把传入的参数赋值给stop
 2
 >>> random.randrange(5,2)           #当只传入两个参数时，必须满足 start < stop   否则会报错哦
 Traceback (most recent call last):
 File "<pyshell#35>", line 1, in <module>
 random.randrange(5,2)
 File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 196, in randrange
 raise ValueError("empty range for randrange() (%d,%d, %d)" % (istart, istop, width))
 ValueError: empty range for randrange() (5,2, -3)
 >>>

 >>> random.randrange(5,5)
 Traceback (most recent call last):
 File "<pyshell#43>", line 1, in <module>
 random.randrange(5,5)
 File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 196, in randrange
 raise ValueError("empty range for randrange() (%d,%d, %d)" % (istart, istop, width))
 ValueError: empty range for randrange() (5,5, 0)
 >>>

 >>> random.randrange(2,5)
 4
 >>>

（五）random.choice(sequence)：从参数序列中从序列中获取一个随机元素。参数sequence表示一个有序类型。

 >>> random.choice('abcdef')
 'f'
 >>> random.choice([1,2,3])
 3
 >>> random.choice(1,2,3)
 Traceback (most recent call last):
   File "<pyshell#58>", line 1, in <module>
     random.choice(1,2,3)
 TypeError: choice() takes 2 positional arguments but 4 were given
 >>> random.choice((1,2,3))
 3
 >>> random.choice(1,3)
 Traceback (most recent call last):
   File "<pyshell#60>", line 1, in <module>
     random.choice(1,3)
 TypeError: choice() takes 2 positional arguments but 3 were given
 >>> random.choice(range(1,5))
 3
 >>> random.choice(random.random())
 Traceback (most recent call last):
   File "<pyshell#62>", line 1, in <module>
     random.choice(random.random())
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 253, in choice
     i = self._randbelow(len(seq))
 TypeError: object of type 'float' has no len()
 >>> random.choice(random.randint(1,5))
 Traceback (most recent call last):
   File "<pyshell#63>", line 1, in <module>
     random.choice(random.randint(1,5))
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 253, in choice
     i = self._randbelow(len(seq))
 TypeError: object of type 'int' has no len()
 >>> 

（六）：random.shuffle(x[, random])，用于将一个列表中的元素打乱。

 >>> l = [1,2,3,4,5]
 >>> random.shuffle(l)
 >>> l
 [3, 2, 1, 4, 5]
 >>>
 >>> t = (1,2,3,4,5)         #下面这两个报错的例子说明了shuffle函数的参数不能是不可变类型的序列。
 >>> random.shuffle(t)
 Traceback (most recent call last):
   File "<pyshell#80>", line 1, in <module>
     random.shuffle(t)
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 272, in shuffle
     x[i], x[j] = x[j], x[i]
 TypeError: 'tuple' object does not support item assignment
 >>> s='my name is wangmanyi'
 >>> random.shuffle(s)
 Traceback (most recent call last):
   File "<pyshell#82>", line 1, in <module>
     random.shuffle(s)
   File "C:\Users\dddd\AppData\Local\Programs\Python\Python35\lib\random.py", line 272, in shuffle
     x[i], x[j] = x[j], x[i]
 TypeError: 'str' object does not support item assignment
 >>> 

（六）random.sample(sequence, k)，从指定序列中随机获取指定长度的片断。sample函数不会修改原有序列。

 >>> l = [1,2,3,4,5,6,7,8,9,10]
 >>> random.sample(l,3)
 [1, 10, 3]
 >>>
 >>> t = (1,2,3,4,5,6,7,8,9,10)
 >>> random.sample(t,3)
 [3, 1, 8]
 >>>
 >>> s = 'my name is wangmany'
 >>> random.sample(s,3)
 ['n', 'm', 'i']

上面只是整理了一部分常用的random中的函数，将来工作中应该够用了。