python中的生成器

前言

列表推导式

列表推导式可以帮助我们快速得到一个我们需要的列表

得到一个1到20的列表

a = [x for x in range(1,21)]
print(a)

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

得到一个1到20内的偶数列表

a = [x for x in range(1,21) if x%2 == 0]
print(a)

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

得到九九乘法表

a = [x*y for x in range(1,10) for y in range(1,10)]
print(a)

[1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 4, 6, 8, 10, 12, 14, 16, 18, 3, 6, 9, 12, 15, 18, 21, 24, 27, 4, 8, 12, 16, 20, 24, 28, 32, 36, 5, 10, 15, 20, 25, 30, 35, 40, 45, 6, 12, 18, 24, 30, 36, 42, 48, 54, 7, 14, 21, 28, 35, 42, 49, 56, 63, 8, 16, 24, 32, 40, 48, 56, 64, 72, 9, 18, 27, 36, 45, 54, 63, 72, 81]

列表生成器

列表生成器的语法与列表推导式的语法很相似，只需要将[ ]换成（）

语法：（ i for i in range（1,10））

它返回的是对象

a = (i for i in range(1,7))
print(a)

at 0x0000013F8FB0DB30>

因此我们想要拿到其中的元素需要使用next（）

next（）相当于一个指针，并且不会回退直到抛出异常

a = (i for i in range(1,7))
print(next(a))
print(next(a))
print(next(a))
print(next(a))
print(next(a))
print(next(a))
print(next(a))

1
2
3
4
5
6
Traceback (most recent call last):
  File "E:\PyCharm\python\text.py", line 8, in
    print(next(a))
StopIteration

Process finished with exit code 1

生成器函数

普通函数：

#斐波那契数列
def febonacci(num):
    a = []
    index = 0
    first = 1
    second = 1
    while index < num:
        a.append(first)
        first,second = second,first+second
        index += 1
    print(a)
 
if __name__ ==  "__main__":
    febonacci(10)

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

生成器函数：

#斐波那契数列
def febonacci(num):
    index = 0
    first = 1
    second = 1
    while index < num:
        yield first
        first,second = second,first+second
        index += 1
 
 
if __name__ ==  "__main__":
    res = febonacci(10)
    i = 0
    while i < 10:
        i += 1
        print(next(res))

1
1
2
3
5
8
13
21
34
55