13.2生成器

""""""
"""1.生成器"""

"""
生成器:用户自定义的迭代器,本质就是迭代器

"""
# def func():
#     print('first')
#     yield  666  # 函数内如果有yield关键字,那么加括号执行函数的时候并不会触发函数体代码的运行
#     print('second')
#     yield  777
#     print('third')
#     yield  888
#     print('forth')
#     yield
#     yield
# # yield后面跟的值就是调用迭代器__next__方法你能得到的值
# # yield既可以返回一个值也可以返回多个值 并且多个值也是按照元组的形式返回
# g = func()  # 生成器初始化:将函数变成迭代器
# print(g)
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())



# print(range(1,10))

# for i in range(1,10,2):
#     print(i)

def my_range(start,end,step=1):
    while start < end:
        yield start
        start += step


for j in my_range(1,100,2):
    print(j)





"""2.生成器表达式"""

# 列表生成式
# res = [i for i in range(1,10) if i != 4]
# print(res)

# res = (i for i in range(1,100000000) if i != 4)  # 生成器表达式
# print(res)
# """
# 生成器不会主动执行任何一行代码
# 必须通过__next__触发代码的运行
# """
# print(res.__next__())
# print(res.__next__())
# print(res.__next__())
# print(res.__next__())


# 占内存
# f = open('13.迭代器,生成器,常用内置方法','r',encoding='utf-8')
# data = f.read()
# print(len(data))
# f.close()


# with open('13.迭代器,生成器,常用内置方法','r',encoding='utf-8') as f:
#     # n = 0
#     # for line in f:
#     #     n += len(line)
#     # print(n)
#     g = (len(line) for line in f)
#     # print(g.__next__())
#     # print(g.__next__())
#     # print(g.__next__())
#     # print(g.__next__())
#     print(sum(g))



def add(n,i):
    return n+i
def test():
    for i in range(4):
        yield i
g=test()

for n in [1,10]:
    g=(add(n,i) for i in g)
    # 第一次for循环g=(add(n,i) for i in test())

    # 第二次for循环g=(add(n,i) for i in (add(n,i) for i in test()))
print(n)
res=list(g)

"""
for i in (add(10,i) for i in test()):  会执行所有的生成器内部的代码
    add(n,i)
"""




#A. res=[10,11,12,13]
#B. res=[11,12,13,14]
#C. res=[20,21,22,23]  答案
#D. res=[21,22,23,24]