Python转换itertools.chain对象为数组的方法

list_of_numbers = [[1, 2], [3], []]
import itertools
chain = itertools.chain(*list_of_numbers)

>>> import numpy as np
>>> from itertools import chain
>>> list_of_numbers = [[1, 2], [3], []]
>>> np.fromiter(chain(*list_of_numbers), dtype=int)
array([1, 2, 3])

>>> list_of_numbers = [[1, 2]*1000, [3]*1000, []]*1000
>>> %timeit np.fromiter(chain(*list_of_numbers), dtype=int)
10 loops, best of 3: 103 ms per loop
>>> %timeit np.array(list(chain(*list_of_numbers)))
1 loops, best of 3: 199 ms per loop

# -*- coding:utf-8 -*-
from itertools import chain
from random import randint
# 随机生成 19 个整数（在 60 到 100 之间）
c1 = [randint(60, 100) for _ in range(19)]
# 随机生成 24 个整数（在 60 到 100 之间）
c2 = [randint(60, 100) for _ in range(24)]
# 随机生成 42 个整数（在 60 到 100 之间）
c3 = [randint(60, 100) for _ in range(42)]
# 随机生成 22 个整数（在 60 到 100 之间）
c4 = [randint(60, 100) for _ in range(22)]
count = 0
# chain()可以把一组迭代对象串联起来，形成一个更大的迭代器
for s in chain(c1, c2, c3, c4):
  if s > 90:
    count += 1
print('4 个班单科成绩大于 90 分的人次为', count)