迭代器

迭代器能减少内存空间实现循环。

方法1：

import time
from collections import Iterable
from collections import Iterator


class Classmate(object):


    def __init__(self):
        self.names = list()


    def add(self,name):
        self.names.append(name)


    def __iter__(self):
        """如果想要一个对象变成一个可以迭代的对象，即可以使用for,那么必须实现__iter__方法"""
        return Classmator(self);  # 调用Classmator 然后把自己传过去


class Classmator(object):
    def __init__(self,obj):
        self.obj = obj
        # 定义索引值
        self.current_num = 0

    def __iter__(self):
        pass


    def __next__(self):
        # 判断索引值是否超出列表个数范围
        if self.current_num < len(self.obj.names):
            ret = self.obj.names[self.current_num]
            # 索引值+1
            self.current_num += 1
            return ret
        else:
            # 抛出异常，终止for循环
            raise StopIteration

classmate = Classmate()

classmate.add("张三")
classmate.add("张二")
classmate.add("李四")

# 判断一个类型是否可以迭代   isinstance(要判断的对象，Iterable)
print("判断classmate是否是可以迭代的对象：", isinstance(classmate,Iterable))
# 迭代器
classmate_iterator = iter(classmate)
# 判断classmate_iterator是否是迭代器
print("判断classmate_iterator是否是迭代器：", isinstance(classmate_iterator,Iterator))
# print(next(classmate_iterator))

for name in classmate:
    print(name)
    time.sleep(1)

两个类可以改善成一个，只要有__iter__方法和__next__方法：

import time
from collections import Iterable
from collections import Iterator



class Classmate(object):
    def __init__(self):
        self.names = list()
        self.current_num = 0

    def add(self,name):
        self.names.append(name)


    def __iter__(self):
        return self


    def __next__(self):
        if self.current_num < len(self.names):
            ret = self.names[self.current_num]
            self.current_num += 1
            return ret
        else:
            raise StopIteration


classmate = Classmate()
classmate.add("张三")
classmate.add("李四")
classmate.add("王五")

# 判断一个类型是否可以迭代   isinstance(要判断的对象，Iterable)
print("判断classmate是否是可以迭代的对象：", isinstance(classmate,Iterable))
# 迭代器
classmate_iterator = iter(classmate)
# 判断classmate_iterator是否是迭代器
print("判断classmate_iterator是否是迭代器：", isinstance(classmate_iterator,Iterator))
# print(next(classmate_iterator))

for name in classmate:
    print(name)
    time.sleep(1)