python中的for循环底层原理详解

一、构建一个可迭代对象（列表、元组、字典等）

#tuple01、dict01自带有__iter__属性，即为可迭代对象
tuple01 = ("Stay hungry Stay foolish","Keep looking,don't sate","hobbies")
dict01 = {"Steve Jobs":1001,"Bill Gates":1002,"near Object":1003}

二、用for循环来进行迭代
(1). 代码如下所示：

for tuple01_i in tuple01:
	print(tuple01_i)
#  for dict01_i in tuple01:
#      print(dict01_i)

(2). 结果如下：

Stay hungry Stay foolish
Keep looking,don't sate
hobbies

三、使用for循环底层原理来进行迭代
(1). 代码如下所示：

# 1.获取可迭代对象的迭代器
# iterator = tuple01.__iter__()
iterator = dict01.__iter__()
while True:
    try:
        # 2.使用迭代器取所有的下一个元素并显示
        item = iterator.__next__()
        # print(item)
        print(item+":",dict01[item])
    # 3.遇到异常停止迭代
    except StopIteration:
        break

(2). 结果如下：

Steve Jobs: 1001
Bill Gates: 1002
near Object: 1003

四、用for循环以及其底层原理来迭代图形类对象
(1). 代码如下所示：

#encoding = utf-8
"""
@version:3.7
@author:qiu
@file:iter_demo.py
@time:23:18
"""
class Graphical: #图形类
    pass

class GraphicalManager: #图像管理器类
    def __init__(self):
        self.__graphs = []

    def add(self,graph):
        self.__graphs.append(graph)

    # 1.创建可迭代对象，有__iter__方法就是可迭代对象
    def __iter__(self):
        return GradphicalIterator(self.__graphs)

class GradphicalIterator: #图形迭代器类
    def __init__(self,graphs):
        self.__graphs = graphs
        self.__index = -1

    def __next__(self): #2.创建迭代器,有__next__方法就是迭代器
        self.__index += 1
        if self.__index > len(self.__graphs) - 1:
            raise StopIteration  #3.迭代完所有图形后，停止迭代
        return self.__graphs[self.__index]

graph_m = GraphicalManager()
graph_m.add(Graphical())
graph_m.add(Graphical())
graph_m.add(Graphical())

#for循环遍历所有图像类对象
for graphical_i in graph_m:
    print("1.图像对象：",graphical_i)

#for循环底层原理遍历所有图像类对象
iterator = graph_m.__iter__()
while True:
    try:
        item = iterator.__next__()
        print("2.图形对象：",item)
    except StopIteration:
        break

(2). 结果如下：

1.图像对象： <__main__.Graphical object at 0x0000016F03B42F08>
1.图像对象： <__main__.Graphical object at 0x0000016F03B42F48>
1.图像对象： <__main__.Graphical object at 0x0000016F03B42F88>
2.图形对象： <__main__.Graphical object at 0x0000016F03B42F08>
2.图形对象： <__main__.Graphical object at 0x0000016F03B42F48>
2.图形对象： <__main__.Graphical object at 0x0000016F03B42F88>