Python从题目中学习：random() module

最近在给公司培训Python，布置了一道题：

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Generate 10 random floats(value range is (-2.0,2.0) and precision is 1) and save as list;

Such as: [-0.7, 0.8, 1.6, 0.1, 0.3, -1.0, 0.4, 1.0, 0.5, 0.7] ;

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因为用到了random模块，在此做一个总结：

random()	类似于uniform()，只不过下限恒等于0.0,上限恒等于1.0
randint()	两个整型参数，返回二者之间的随机整型
randrange()	它接受和range()函数一样的参数，随机返回range([start,]stop[,step])结果的一项
uniform()	几乎和randint()一样，不过他返回的是二者之间的一个浮点型(不包括范围上限)
sample(seq,k)	从指定序列中随机获取指定长度的片断
choice()	随机返回给定序列的一个元素
shuffle()	用于将一个列表中的元素打乱

random模块用于生成随机数，下面列举几个常用的函数。

①random.random

| random(...)
| random() -> x in the interval [0, 1).

random.random()用于生成一个0到1的随机符点数: 0 <= n < 1.0

>>> random.random()

0.7361643505007011

②random.uniform

| uniform(self, a, b)
| Get a random number in the range [a, b) or [a, b] depending on rounding.

random.uniform(a, b)，用于生成一个指定范围内的随机符点数。

如果 a>b，则生成的随机数n在[a,b]之间: a <= n <= b；

如果 a<b，则生成的随机数n在[a,b]之间: b <= n <= a。

>>> random.uniform(10,20)

18.084480262346535

>>> random.uniform(20,10)

12.289824189134892

③random.choice

| choice(self, seq)
| Choose a random element from a non-empty sequence.

random.choice(self, seq)会从序列中获取一个随机元素。

参数seq表示一个有序类型。字符串，list，tutple都属于sequence。

>>> random.choice("PythonRandomModule")#字符串

'P'

>>> random.choice(["Delon","is","a","nice","boy"])#列表

'a'

>>> random.choice(("Tuple1","Tuple2","Tuple3"))#元组

'Tuple1'

④random.randint

| randint(self, a, b)
| Return random integer in range [a, b], including both end points.

random.randint(a, b)，用于生成一个指定范围内的整数。生成的随机数n在[a,b]之间: a <= n <= b。（结束点b必须大于起始点a。）

>>> random.randint(2,10)#随机数在[2,10]之间

8

>>> random.randint(10,10)#结果永远是10

>>> random.randint(10,2)#语法错误

raise ValueError, "empty range for randrange() (%d,%d, %d)" % (istart, istop, width)

ValueError: empty range for randrange() (10,3, -7)

⑤random.randrange

| randrange(self, start, stop=None, step=1, _int=<type 'int'>, _maxwidth=9007199254740992L)
| 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.

random.randrange([start], stop[, step]) 在指定范围内，获取一个随机数从指定的step生成的递增集合中。

比如random.randrange(10,100,2),就相当于从[10,12,14,16,18,.....,94,96,98]的序列中获取一个随机数。

random.randrange(10,100,2)与random.choice(range(10,100,2))一样。

>>> random.randrange(10,100,2)

>>> random.choice(range(10,100,2))

⑥random.sample

| sample(self, population, k)
| Chooses k unique random elements from a population sequence.
|
| 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 xrange as an argument.
| This is especially fast and space efficient for sampling from a
| large population: sample(xrange(10000000), 60)
|

random.sample(sequence, k)，从指定序列中随机获取指定长度的片断。

>>> list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> slice = random.sample(list,5)

>>> slice

[6, 5, 10, 9, 2]

>>> list#原序列不会因为sample而改变

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

⑦random.shuffle

>>> list = ["Python","is","powerful","languange"]

>>> random.shuffle(list) #打乱

>>> list

['powerful', 'is', 'languange', 'Python']

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接下来举几个例子：

例子1：(参考http://www.cnblogs.com/yd1227/archive/2011/03/18/1988015.html):

#随机生成[0,99]的整数：

>>> import random

>>> random.randint(0,99)

21

#随机选取0到100间的偶数：

>>> random.randrange(0, 101, 2)

42

#随机浮点数：

>>> random.random()

0.85415370477785668

>>> random.uniform(1, 10)

5.4221167969800881

#随机字符：

>>> import random

>>> random.choice('abcdefg&#%^*f')

'd'

#多个字符中选取特定数量的字符：

>>> random.sample('abcdefghij',3)

['a', 'd', 'b']

#多个字符中选取特定数量的字符组成新字符串：

>>> import string

>>> string.join(random.sample(['a','b','c','d','e','f','g','h','i','j'], 3)).replace(" ","")

'fih'

#随机选取字符串：

>>> random.choice ( ['apple', 'pear', 'peach', 'orange', 'lemon'] )

'lemon'

#洗牌：

>>> import random

>>> items = [1, 2, 3, 4, 5, 6]

>>> random.shuffle(items)

>>> items

[3, 2, 5, 6, 4, 1]

例子2：(参考http://blog.csdn.net/xiaocaiju/article/details/6973175):

import random

result = random.random()

print result　　  #生成0-1的随机数

0.6595765656210394

print random.uniform(10,12)      #10-12的随机数

10.806990108392618             

print random.randint(30,50)　　#30-50的随机整数

50

print random.randrange(10,100,2)     #从10开始到100结束，步长为2的序列中，随机选一个

22

list = [1,2,5,6,7,8,8]

print random.choice(list)         #从序列中随机选一个

5

random.shuffle(list)     #重新排列序列

print list

[5, 2, 1, 6, 8, 8, 7]

list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

slice = random.sample(list, 5)   #从序列中取样

print slice

[7, 3, 2, 5, 10]

现在回到文章开头的问题，代码如下：

"""

Generate 10 random floats(value range is (-2.0,2.0) and precision is 1) and save as list;

Such as: [-0.7, 0.8, 1.6, 0.1, 0.3, -1.0, 0.4, 1.0, 0.5, 0.7] ;

"""

>>> [round(random.uniform(-2,2),1) for i in range(10)]

#[-1.0, -1.0, -1.7, 1.0, -1.1, 1.9, 1.7, 0.2, -0.9, 1.1]