python 2018.7.18

1. 生成器和生成器函数
    生成器的本质就是迭代器
    生成器的三种创建办法:
        1.通过生成器函数
        2.通过生成器表达式创建生成器
        3.通过数据转换
    生成器函数:
        函数中包含了yield的就是生成器函数
        注意:生成器函数被执行. 获取到的是生成器. 而不是函数的执行
    生成器表达式:
        (结果 for 变量 in 可迭代对象 if 筛选)
    取值:
        1. __next__()
        2. send(值) 给上一个yield位置传一个值, 第一个和最后一个yield不用传值
        3. 可以for循环
        4. list(g)
例

# def func():
#     print("我是周杰伦")
#     yield "昆凌"  # 函数中包含了yield, 当前这个函数就不再是普通的函数了. 是生成器函数
#     print("我是王力宏")
#     yield "李云迪???"
#     print("我是笛卡尔积")
#     yield "笛卡尔积是谁"
    # print("你好啊") # 最后一个yield之后如果再进行__next__() 会报错
# g = func()
# print(g.__next__())
# print(func().__next__())
#
# g1 = func()
# g2 = func()
# print(g1.__next__())
# print(g1.__next__())
#
# print("==============")
# print(g2.__next__())

#
# g = func()  # 通过函数func()来创建一个生成器
# print(g.__next__()) # 周杰伦
# print(g.__next__()) # 王力宏
# print(g.__next__()) # 笛卡尔积
# print(g.__next__())

# return 直接返回结果. 结束函数的调用
# yield 返回结果.可以让函数分段执行
#
# def func():
#     lst = []
#     for i in range(1,100001):
#         lst.append("衣服%s" % i)
#     return lst
#
# def gen():
#     i = 1
#     while i < 100001:
#         yield "衣服%s" % i
#         i = i + 1
# g = gen()
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())
# print(g.__next__())

#
# def func():
#     yield 11
#     yield 22
#     yield 33
#     yield 44
#
#
# g = func()  # 拿到的是生成器. 生成器的本质是迭代器. 迭代器可以被迭代 生成器可以直接for循环
#
# for i in g:
#     print(i)    # 本质上执行的是__next__()
#
# it = g.__iter__()
# while True:
#     try:
#         print(it.__next__())
#     except StopIteration:
#         break

# def func():
#     print("大碴粥")
#     a = yield "11"
#     print(a)
#     print("狗不理")
#     b = yield "22"
#     print(b)
#     print("大麻花")
#     c = yield "33"
#     print(c)
#
# g = func()
# print(g.__next__())
# print(g.send(1))
# print(g.send(2))
# print(g.send(3))

# __next__() 可以让生成器向下执行一次
# send() 也可以让生成器向下执行一次, 给上一个yield传一个值, 第一个不能用send(). 最后一个也不要传值

#
# def eat():
#     print("我吃什么啊")
#     a =  yield  "馒头"
#     print("a=",a)
#     b =  yield  "大饼"
#     print("b=",b)
#     c =  yield  "韭菜盒子"
#     print("c=",c)
#     yield  "GAME OVER"
#
# gen = eat()      # 获取⽣成器
#
# ret1 = gen. __next__ ()
# print(ret1)
# ret2 = gen.send("胡辣汤")
# print(ret2)
# ret3 = gen.send("狗粮")
# print(ret3)
# ret4 = gen.send("猫粮")
# print(ret4)
#
#
# def func():
#     yield 11
#     yield 22
#     yield 33
#     yield 44
# g = func()
# lst = list(g)   # 可迭代对象
# print(lst)


2. 各种推倒式和生成器表达式
    1. 列表推倒式 [结果 for 变量 in 可迭代对象 if 筛选]
    2. 字典推倒式 {结果 for 变量 in 可迭代对象 if 筛选} 结果=>key:value
    3. 集合推倒式 {结果 for 变量 in 可迭代对象 if 筛选} 结果=>key
例

# 生成列表 里面装1-14的数据
# lst = []
# for i in range(1,15):
#     lst.append("python%s" % i)
# print(lst)

# 列表推倒式; 最终给你的是列表
# 语法 [最终结果(变量) for 变量 in 可迭代对象]

# lst = [i for i in range(1,15)]
# print(lst)

# [最终结果 for 变量 in 可迭代对象 if 条件]
lst = [i for i in range(1,101) if i%2==0]
print(lst)

# 1. 获取1-100内能被3整除的数
# lst = [i for i in range(1,101) if i % 3 == 0]
# 2. 100以内能被3整除的数的平方
# lst = [i*i for i in range(1,101) if i % 3 == 0]
# 3. 寻找名字中带有两个e的⼈的名字
# names = [['Tom', 'Billy', 'Jefferson' , 'Andrew' , 'Wesley' , 'Steven' ,
# 'Joe'],['Alice', 'Jill' , 'Ana', 'Wendy', 'Jennifer', 'Sherry' , 'Eva']]
# lst = [name for first in names for name in first if name.count("e") == 2]
# print(lst)
#
# lst = ["衣服%s" % i for i in range(10000)]

# g = (i for i in range(10))
# print(list(g))

# gen = ("麻花藤我第%s次爱你" % i for i in  range(10))
# for i in  gen:
#     print(i)

# 生成器的惰性机制
# def func():
#     print(111)
#     yield  222
# g = func()
# g1 = (i  for i in  g)
# g2 = (i  for i in  g1)
#
# print(list(g))
# print(list(g1))
# print(list(g2))

# dic = {"a":"b", "c":"d"}
# # 把字典中的key:value互换 .{"b":"a", "d":"c"}
# new_dic = {dic[key]:key for key in dic}
# print(new_dic)

# lst1 = ["alex", "wusir", "taibai", "ritian"]
# lst2 = ['sb', "很色", "很白", "很牛"]
# # {"alex":"sb", "wusir":"很色"}
#
# dic = { lst1[i]:lst2[i] for i in range(len(lst1))}
# print(dic)

lst = ["马化腾", "马化腾", "王建忠", "张建忠", "张建忠", "张雪峰", "张雪峰"]

s = {i for i in lst}    # 集合推倒式
print(s)

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