python笔记14—day14

1、生成器函数进阶

1.1、send

def generator():
    print(123)
    content = yield 1
    print('=======',content)
    print(456)
    arg = yield 2

g = generator()
ret = g.__next__()
print('***',ret)
ret = g.send('hello')   #send的效果和next一样
print('***',ret)

#结果：
    #123
    #*** 1
    #======= hello
    #456
    #*** 2

send 获取下一个值的效果和next基本一致
只是在获取下一个值的时候，给上一yield的位置传递一个数据
使用send的注意事项
　　第一次使用生成器的时候是用next获取下一个值
　　最后一个yield不能接受外部的值

1.2、移动数据求平均值

def average():
    sum = 0
    count = 0
    avg = 0
    while True:
        num = yield avg
        sum += num    # 10
        count += 1    # 1
        avg = sum/count

avg_g = average()
avg_g.__next__()
avg1 = avg_g.send(10)
avg1 = avg_g.send(20)
avg1=avg_g.send(30)
print(avg1)

#预激生成器的装饰器
def init(func):   #装饰器
    def inner(*args,**kwargs):
        g = func(*args,**kwargs)    #g = average()
        g.__next__()
        return g
    return inner

@init
def average():
    sum = 0
    count = 0
    avg = 0
    while True:
        num = yield avg
        sum += num    # 10
        count += 1    # 1
        avg = sum/count

avg_g = average()   #===> inner
ret = avg_g.send(10)
print(ret)
ret = avg_g.send(20)
print(ret)

2、生成器表达式

egg_list=['鸡蛋%s'%i for i in range(10)]    #列表推导式
print(egg_list)

egg_list = []
for i in range(10):
    egg_list.append('鸡蛋%s'%i)
print(egg_list)

#两种方法的结果相等

#生成器表达式
g = (i for i in range(10))
print(g)
for i in  g:
    print(i)

3、各种推导式

#30以内所有能被3整除的数
ret = [i for i in range(30) if i%3 == 0]  #完整的列表推导式
print(ret)
g = (i for i in range(30) if i%3 == 0)  #完整的列表推导式
print(g)
li=[]
for i in g:
    li.append(i)
print(li)

# 例三:找到嵌套列表中名字含有两个‘e’的所有名字
names = [['Tom', 'Billy', 'Jefferson', 'Andrew', 'Wesley', 'Steven', 'Joe'],
         ['Alice', 'Jill', 'Ana', 'Wendy', 'Jennifer', 'Sherry', 'Eva']]
ret = [name for lst in names for name in lst if name.count('e') ==2]
print(ret)
g = (name for lst in names for name in lst if name.count('e') ==2)
print(g)
li=[]
for i in g:
    li.append(i)
print(li)

# 将一个字典的key和value对调
mcase = {'a': 10, 'b': 34}
#{10:'a' , 34:'b'}
mcase_frequency = {mcase[k]: k for k in mcase}
print(mcase_frequency)

# 合并大小写对应的value值，将k统一成小写
mcase = {'a': 10, 'b': 34, 'A': 7, 'Z': 3}
#{'a':10+7,'b':34,'z':3}
mcase_frequency = {k.lower(): mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0) for k in mcase}
print(mcase_frequency)

#集合推导式，自带结果去重功能
squared = {x**2 for x in [1, -1, 2]}
print(squared)

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