生成器

生成器就是只能迭代一次的迭代器,生成器的目的是优化内存资源。

# generator version
def fibon(n):
    a = b = 1
    for i in range(n):
        yield a
        a, b = b, a + b

image.png

#function return version
def fibon(n):
    a = b = 1
    result = []
    for i in range(n):
        result.append(a)
        a, b = b, a + b
    return result

image.png

对比返回生成器与直接用数组存储内存的占用差别

---

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

#without generator
def process_list(my_list):
    for i in range(len(my_list)):
        my_list[i] *= 2
    return my_list

#with generator
def process_list_with_generaotr(my_list):
    for i in range(len(my_list)):
        yield my_list[i] * 2


print(process_list(my_list))
print(process_list_with_generaotr(my_list))

image.png

yield返回的是一个generator Object

---

def generator_function():
    for i in range(3):
        yield i

gen = generator_function()
print(next(gen))
# Output: 0
print(next(gen))
# Output: 1
print(next(gen))
# Output: 2
print(next(gen))
# Output: Traceback (most recent call last):
#            File "<stdin>", line 1, in <module>
#         StopIteration

只能迭代一次