python从列表中随机取数

从列表arr中随机选择k个数据。选出的数据在arr中的位置不重复。k小于等于arr的长度

1. random.sample(arr,k)

import random
value = [1,2,3,4]
r = random.sample(value,4) ## 随机选出4个数
print(r)
r = random.sample(value,5) ## 报错
print(r)

当大于数组长度时，报错如下

raise ValueError("Sample larger than population or is negative")
ValueError: Sample larger than population or is negative

python 手册解释

random.sample(population, k)

Return a k length list of unique elements chosen from the population sequence or set. Used for random sampling without replacement.

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).
（保证取出数据在列表中的位置不重复）

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 from a range of integers, use a range() object as an argument. This is especially fast and space efficient for sampling from a large population: sample(range(10000000), k=60).

If the sample size is larger than the population size, a ValueError is raised.