python基础之迭代器与生成器

lst = [1,2,3,4]
it = iter(lst) #创建迭代器对象
print(it) # <list_iterator object at 0x7fb8e443ed30>
print(next(it)) # 1
print(next(it)) # 2

lst = [1,2,3,4]
it = iter(lst) #创建迭代器对象
for x in it:
    print(x, end=" ") # 1 2 3 4 

import sys  # 引入 sys 模块

lst = [1, 2, 3, 4]
it = iter(lst)  # 创建迭代器对象

while True:
    try:
        print(next(it))
    except StopIteration:
        sys.exit()

class MyNumbers:
    def __iter__(self):
        self.a = 1
        return self

    def __next__(self):
        if self.a <= 10: #迭代次数，要不然for循环会一直执行
            x = self.a
            self.a += 1
            return x
        else:
            raise StopIteration


myclass = MyNumbers()
myiter = iter(myclass) 

for x in myiter: #这里也可以直接用对象，因为它的类已经定义iter和next。
    print(x,end = " ") # 1 2 3 4 5 6 7 8 9 10

def func(n):
    yield n*2

f = func(5)
print(f) # <generator object func at 0x7f36613ad308>
print(next(f)) # 10，迭代器的值
print(next(f)) # 报错！！！因为这个函数只返回了一个迭代器

def fib(n):
    pre,curr = 0,1
    while n > 0:
        n-=1
        yield curr
        pre,curr = curr,curr+pre
        print("I am a generator!")

for i in fib(5):
    print(i)
    print("-----------------------")

1
-----------------------
I am a generator!
1
-----------------------
I am a generator!
2
-----------------------
I am a generator!
3
-----------------------
I am a generator!
5
-----------------------
I am a generator!

def func(n):
    yield n*2
    print("I am a generator!")

f = func(5)
print(f) # <generator object func at 0x7f36613ad308>
print(next(f)) # 10，迭代器的值

g = (i*2 for i in range(10))
print(type(g)) # <class 'generator'>

for i in g:
    print(i,end=" ") # 0 2 4 6 8 10 12 14 16 18