迭代器_装饰器_生成器_推导式

def tail(filename):
    f = open(filename,encoding='utf-8')
    while True:
        line = f.readline()
        if line.strip():
            yield line.strip()

g = tail('file')
for i in g:
    if 'python' in i:
        print('***',i)

#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) #传入参数
print(ret)
ret = avg_g.send(20)
print(ret)

# send
    # send的作用范围和next一模一样
    # 第一次不能用send
    # 函数中的最后一个yield不能接受新的值

#python 3
def generator():
    a = 'abcde'
    b = '12345'
    yield from a
    yield from b

g = generator()
for i in g:
    print(i)

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

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

#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

# 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)

# 例一：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)

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