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)