一、迭代器：
1、迭代：每一次对过程的重复称为一次“迭代”，而每一次迭代得到的结果会作为下一次迭代的初始值。例如：循环获取容器中的元素。
2、可迭代对象（iterable)：
1）定义：具有__iter__函数的对象，可以返回迭代器对象。
2）语法：
3）原理：
3、迭代器对象（iterator)：
1）定义：可以被next()函数调用并返回下一个值的对象。
2）语法：
3）说明及作用：
二、生成器（generator）：
三、生成器函数：
四、基础代码：
代码1：
""" 可迭代对象：具有__iter__()方法，可以返回迭代器的对象． """ list01 = [2,434,5,6,8] # for item in list01: # print(item) # 面试题： # 能够被for循环的条件是：可迭代对象（具有__iter__()方法的对象） # for循环原理 # 1. 获取迭代器对象 # 2. 循环迭代(调用迭代器的__next__方法) # 3. 捕获StopIteration异常 #1. # iterator = list01.__iter__() #2. # item = iterator.__next__() # print(item) # # item = iterator.__next__() # print(item) # # item = iterator.__next__() # print(item) # # item = iterator.__next__() # print(item) # # item = iterator.__next__() # 最后一次 # print(item) # 3. # item = iterator.__next__()# StopIteration # print(item) # 1. 获取迭代器对象 iterator = list01.__iter__() while True: try:# 如果获取了全部元素,则执行except # 2. 获取下一个元素(迭代过程) item = iterator.__next__() print(item) # 3.停止迭代（StopIteration 错误） except StopIteration: break # 跳出循环体
代码2：
""" 迭代器 """ class Skill: pass class SkillIterator: """ 技能迭代器 """ def __init__(self, target): self.target = target self.index = 0 def __next__(self): # 如果索引越界 则抛出异常 if self.index > len(self.target) - 1: raise StopIteration() # 返回下一个元素 item = self.target[self.index] self.index += 1 return item class SkillManager: """ 可迭代对象 """ def __init__(self, skills): self.skills = skills def __iter__(self): # 创建迭代器对象 传递 需要迭代的数据 return SkillIterator(self.skills) #---------------以下是客户端代码--------------------- manager = SkillManager([Skill(), Skill(), Skill()]) # for item in manager.skills: for item in manager:# 获取manager对象中列表元素(获取manager对象的聚合类型对象元素) print(item) # iterator = manager.__iter__() # while True: # try: # item = iterator.__next__() # print(item) # except: # break
代码3：
""" 迭代器 --> yield """ class Skill: pass # class SkillIterator: # """ # 技能迭代器 # """ # def __init__(self, target): # self.target = target # self.index = 0 # # def __next__(self): # if self.index > len(self.target) - 1: # raise StopIteration() # item = self.target[self.index] # self.index += 1 # return item class SkillManager: def __init__(self, skills): self.skills = skills # def __iter__(self): # return SkillIterator(self.skills) def __iter__(self): """ 执行过程： １．调用__iter__()方法不执行 ２．调用__next__()方法时执行，到yield语句暂时离开． ３．再次调用__next__()方法时，从上次离开的代码开始执行，到yield语句暂时离开 4. 待执行完方法体，抛出StopIteration异常． 原理：如果方法体中包含yield关键字，那么会自动生成迭代器对象． 生成迭代器代码的大致规则： 1. 将yield关键字以前的代码，放到__next__方法中． 2. 将yield关键字以后的数据，作为__next__方法的返回值 """ # print("准备返回第一个元素") # yield self.skills[0] # 暂时离开点 再次执行点 # # print("准备返回第二个元素") # yield self.skills[1] # # print("准备返回第三个元素") # yield self.skills[2] for item in self.skills: yield item #---------------以下是客户端代码--------------------- manager = SkillManager([Skill(), Skill(), Skill()]) # for item in manager: # print(item) iterator = manager.__iter__() while True: try: item = iterator.__next__() print(item) except Exception as e: print(e) break
代码4：
""" yield －－＞ 生成器函数 """ # class MyRange: # def __init__(self, stop): # self.stop = stop # # def __iter__(self): # start = 0 # while start < self.stop: # yield start # start += 1 # # for item in MyRange(5): # print(item) # 生成器函数 def my_range(stop): start = 0 while start < stop: yield start start += 1 # for item in my_range(5): # print(item) iter01 = my_range(5) for item in iter01: print(item)
五、练习实例：
练习1：
# 练习１：("悟空","八戒","沙僧","唐僧") # 使用while + 迭代器 获取元组所有元素 t01 = ("悟空", "八戒", "沙僧", "唐僧") iterator = t01.__iter__() while True: try: item = iterator.__next__() print(item) except: break # 练习２：{"张三丰"：101,"张无忌":102,"赵敏":102} # 不使用for循环，获取字典所有元素． d01 = {"张三丰": 101, "张无忌": 102, "赵敏": 102} iterator = d01.__iter__() while True: try: key = iterator.__next__() print(key, d01[key]) except: break
练习2：
""" 练习：迭代员工管理器对象 """ class Employee: pass class EmployeeIterator: """ 迭代器 """ def __init__(self, target): self.target = target self.index = 0 def __next__(self): if self.index > len(self.target) - 1: raise StopIteration() item = self.target[self.index] self.index += 1 return item # 可迭代对象 class EmployeeManager: def __init__(self, employees): self.all_employee = employees def __iter__(self): # 返回迭代器 return EmployeeIterator(self.all_employee) manager = EmployeeManager([Employee(), Employee()]) # 需求：ｆｏｒ循环自定义类的对象 # for item in manager: # print(item) # iterator = manager.__iter__() while True: try: item = iterator.__next__() print(item) except: break
练习3：
""" 参照下列代码，定义ＭｙＲａｎｇｅ类，实现相同效果． """ # 15:40 class MyRangeIterator: def __init__(self, stop): self.stop = stop self.start = 0 def __next__(self): if self.start + 1 > self.stop: raise StopIteration() temp = self.start self.start += 1 return temp class MyRange: def __init__(self, stop): self.stop = stop def __iter__(self): # 创建迭代器对象 return MyRangeIterator(self.stop) # for item in range(5): # print(item)# # for item in MyRange(5): # print(item)#0 1 2 3 4 iterator = MyRange(5) for item in iterator: print(item) # # iterator = iterator.__iter__() # while True: # try: # item = iterator.__next__() # print(item) # except: # break
练习4：
""" 改造为yield实现 """ class Employee: pass # class EmployeeIterator: # """ # 迭代器 # """ # def __init__(self, target): # self.target = target # self.index = 0 # # def __next__(self): # if self.index > len(self.target) - 1: # raise StopIteration() # item = self.target[self.index] # self.index += 1 # return item # 可迭代对象 class EmployeeManager: def __init__(self, employees): self.all_employee = employees # def __iter__(self): # # 返回迭代器 # return EmployeeIterator(self.all_employee) def __iter__(self): for item in self.all_employee: yield item manager = EmployeeManager([Employee(), Employee()]) # 需求：ｆｏｒ循环自定义类的对象 # for item in manager: # print(item) # iterator = manager.__iter__() while True: try: item = iterator.__next__() print(item) except: break
练习5：
""" 改造为yield实现 """ # class MyRangeIterator: # def __init__(self, stop): # self.stop = stop # self.start = 0 # # def __next__(self): # if self.start + 1 > self.stop: # raise StopIteration() # temp = self.start # self.start += 1 # return temp class MyRange: def __init__(self, stop): self.stop = stop # def __iter__(self): # # 创建迭代器对象 # return MyRangeIterator(self.stop) def __iter__(self): start = 0 while start < self.stop: yield start start += 1 iterator = MyRange(5) # for item in iterator: # print(item) # iterator = iterator.__iter__() while True: try: item = iterator.__next__() print(item) except: break
练习6：
""" 生成器函数练习 体会：方法／函数，需要向外返回多个结果时，使用生成器函数． 惰性操作/延迟操作 (生成器函数的"循环(next)一次,计算一次,返回一次") """ list01 = [23,3,4,556,677,68,8,98,98] # 练习１：在list01中，挑出所有偶数． # 要求：1)使用生成器函数实现 def get_even01(target): for item in target: if item % 2 == 0: yield item iter01 = get_even01(list01)# 没有执行方法体 for item in iter01:# 循环(next)一次,计算一次,返回一次 print(item) # def get_even02(target): # result = [] # for item in target: # if item % 2 == 0: # result.append(item) # return result # # iter01 = get_even02(list01)# 执行方法体,将所有结果存在内存中． # for item in iter01: # print(item) # 练习２：定义函数，选出所有女同学. class Student: def __init__(self,name,sex,age,score): self.name = name self.sex = sex self.age = age self.score = score def __str__(self): return "%s--%s--%d--%d"%(self.name,self.sex,self.age,self.score) list_stu = [ Student("张无忌","男",28,82), Student("赵敏","女",25,95), Student("周芷若","女",26,88), ] def find_woman(target): for item in target: if item.sex == "女": yield item for item in find_woman(list_stu): print(item) # 练习３：选出所有成绩大于９０的学生 def find_by_score(target): for item in target: if item.score > 90: yield item for item in find_by_score(list_stu): print(item)