python3 迭代器

'''
总结：
    Iterable: 可迭代对象，有__iter__()方法
    Iterator: 迭代器，有__iter__()和__next__()方法
    迭代器的特点：
        1.节省内存。
        2.惰性机制。
        3.不能反复，只能向下执行。
'''

str1 = "hello"
for s in str1:
    print(s)
'''
h
e
l
l
o
'''

int1 = 123
for i in int1:
    print(i)  # TypeError: 'int' object is not iterable

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-14-8c7f77a7214a> in <module>()
      1 int1 = 123
----> 2 for i in int1:
      3     print(i)

TypeError: 'int' object is not iterable

'''dir函数'''
dir(list)

['__add__',
 '__class__',
 '__contains__',
 '__delattr__',
 '__delitem__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getitem__',
 '__gt__',
 '__hash__',
 '__iadd__',
 '__imul__',
 '__init__',
 '__init_subclass__',
 '__iter__',
 '__le__',
 '__len__',
 '__lt__',
 '__mul__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__reversed__',
 '__rmul__',
 '__setattr__',
 '__setitem__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 'append',
 'clear',
 'copy',
 'count',
 'extend',
 'index',
 'insert',
 'pop',
 'remove',
 'reverse',
 'sort']

print("__iter__" in dir(int))  # False
print("__iter__" in dir(bool))  # False
print("__iter__" in dir(str))  # True
print("__iter__" in dir(list))  # True
print("__iter__" in dir(set))  # True
print("__iter__" in dir(tuple))  # True
print("__iter__" in dir(dict))  # True

'''isinstance()函数可以查看一个对象是什么类型
iterable 迭代对象
iterator 迭代器
'''
lst = ["apple", "banana", "orange"]
lst_iter = lst.__iter__()  # 迭代对象.__iter__()会生成一个迭代器
from collections import Iterable, Iterator
print(isinstance(lst, Iterable))  # True
print(isinstance(lst_iter, Iterable))  # True
print(isinstance(lst, Iterator))  # False
print(isinstance(lst_iter, Iterator))  # True

str1 = "hello"
str_iter = str1.__iter__()
print(str_iter.__next__())  # 迭代器有next方法，如果拿完数据，再执行next会报StopIteration，返回结果：h
print(str1.__next__())  # 迭代对象没有next方法

h

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-18-56c2a1c77dc2> in <module>()
      2 str_iter = str1.__iter__()
      3 print(str_iter.__next__())
----> 4 print(str1.__next__())

AttributeError: 'str' object has no attribute '__next__'

'''for循环机制'''
for i in [1, 2, 3]:
    print(i)

1
2
3

'''使用while循环+迭代器来模拟for循环'''
lst = [1, 2, 3]
lst_iter = lst.__iter__()
while 1:
    try:
        print(lst_iter.__next__())
    except StopIteration:
        break
    

1
2
3

'''list可以一次性把迭代器中的内容拿空，并装载在一个新列表中'''
str1 = "hello".__iter__()
print(list(str1)) # ['h', 'e', 'l', 'l', 'o']