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

---------------------------------------------------------------------------

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)

'''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

'''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']

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python3 迭代器

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