一文讲透 Python 协程 _小知识

迭代1.1 迭代的概念

使用for循环遍历取值的过程叫做迭代，比如：使用for循环遍历列表获取值的过程

for value in [2, 3, 4]:print(value)
1.2 可迭代对象

标准概念：在类里面定义__iter__方法，并使用该类创建的对象就是可迭代对象
简单记忆：使用for循环遍历取值的对象叫做可迭代对象, 比如：列表、元组、字典、集合、range、字符串

【一文讲透 Python 协程】
1.3 判断对象是否是可迭代对象

from collections import Iterableresult = isinstance((3, 5), Iterable)print("元组是否是可迭代对象:", result)result = isinstance([3, 5], Iterable)print("列表是否是可迭代对象:", result)result = isinstance({"name": "张三"}, Iterable)print("字典是否是可迭代对象:", result)result = isinstance("hello", Iterable)print("字符串是否是可迭代对象:", result)result = isinstance({3, 5}, Iterable)print("集合是否是可迭代对象:", result)result = isinstance(range(5), Iterable)print("range是否是可迭代对象:", result)result = isinstance(5, Iterable)print("整数是否是可迭代对象:", result)result = isinstance(5, int)print("整数是否是int类型对象:", result)class Student(object):passstu = Studentresult = isinstance(stu, Iterable)print("stu是否是可迭代对象:", result)result = isinstance(stu, Student)print("stu是否是Student类型的对象:", result)

1.4 自定义可迭代对象

在类中实现__iter__方法

自定义可迭代类型代码

from collections import Iterableclass MyList(object):def __init__(self):self.my_list = listdef Append_item(self, item):self.my_list.append(item)def __iter__(self):passmy_list = MyListmy_list.append_item(1)my_list.append_item(2)result = isinstance(my_list, Iterable)print(result)for value in my_list:print(value)

执行结果:

Traceback (most recent call last):TrueFile "/Users/hbin/Desktop/untitled/aa.py", line 24, in <module>for value in my_list:TypeError: iter returned non-iterator of type 'NoneType'

通过执行结果可以看出来，遍历可迭代对象依次获取数据需要迭代器

总结在类里面提供一个__iter__创建的对象是可迭代对象，可迭代对象是需要迭代器完成数据迭代的

2、迭代器2.1 自定义迭代器对象

自定义迭代器对象: 在类里面定义__iter__和__next__方法创建的对象就是迭代器对象

from collections import Iterablefrom collections import Iteratorclass MyList(object):def __init__(self):self.my_list = listdef append_item(self, item):self.my_list.append(item)def __iter__(self):my_iterator = MyIterator(self.my_list)return my_iteratorclass MyIterator(object):def __init__(self, my_list):self.my_list = my_listself.current_index = 0result = isinstance(self, Iterator)print("MyIterator创建的对象是否是迭代器:", result)def __iter__(self):return selfdef __next__(self):if self.current_index < len(self.my_list):self.current_index += 1return self.my_list[self.current_index - 1]else:raise StopIterationmy_list = MyListmy_list.append_item(1)my_list.append_item(2)result = isinstance(my_list, Iterable)print(result)for value in my_list:print(value)

运行结果:
TrueMyIterator创建的对象是否是迭代器: True12
2.2 iter函数与next函数iter函数: 获取可迭代对象的迭代器，会调用可迭代对象身上的__iter__方法
next函数: 获取迭代器中下一个值，会调用迭代器对象身上的__next__方法

class MyList(object):def __init__(self):self.my_list = listdef append_item(self, item):self.my_list.append(item)def __iter__(self):my_iterator = MyIterator(self.my_list)return my_iteratorclass MyIterator(object):def __init__(self, my_list):self.my_list = my_listself.current_index = 0def __iter__(self):return selfdef __next__(self):if self.current_index < len(self.my_list):self.current_index += 1return self.my_list[self.current_index - 1]else:raise StopIterationmy_list = MyListmy_list.append_item(1)my_list.append_item(2)my_iterator = iter(my_list)print(my_iterator)while True:try:value = https://www.isolves.com/it/cxkf/yy/Python/2021-12-15/next(my_iterator)print(value)except StopIteration as e:break

2.3 for循环的本质遍历的是可迭代对象for item in Iterable 循环的本质就是先通过iter函数获取可迭代对象Iterable的迭代器，然后对获取到的迭代器不断调用next方法来获取下一个值并将其赋值给item，当遇到StopIteration的异常后循环结束。