标签：arm span isl 协议 eof tle ali tty enc
一. 迭代器
1. 可以使用dir()函数来检查类的内部定义的函数
2.特点:
__iter__() 获取迭代器
__next__() 获取最前面这个元素
我们之前?直在?可迭代对象进?迭代操作. 那么到底什么是可迭代对象. 本?节主要讨
论可迭代对象. ?先我们先回顾?下?前我们所熟知的可迭代对象有哪些:
str, list, tuple, dict, set. 那为什么我们可以称他们为可迭代对象呢? 因为他们都遵循了可
迭代协议. 什么是可迭代协议. ?先我们先看?段错误代码:
# 对的
s = "abc"
for c in s:
print(c)
# 错的
for i in 123:
print(i)
结果:
Traceback (most recent call last):
File "/Users/sylar/PycharmProjects/oldboy/iterator.py", line 8, in
<module>
for i in 123:
TypeError: ‘int‘ object is not iterable
注意看报错信息中有这样?句话. ‘int‘ object is not iterable . 翻译过来就是整数类型对象
是不可迭代的. iterable表?可迭代的. 表?可迭代协议. 那么如何进?验证你的数据类型是否
符合可迭代协议. 我们可以通过dir函数来查看类中定义好的所有?法:
s = "我的哈哈哈" print(dir(s)) # 可以打印对象中的?法和函数 print(dir(str)) # 也可以打印类中声明的?法和函数
在打印结果中. 寻找__iter__ 如果能找到. 那么这个类的对象就是?个可迭代对象 .
[‘__add__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__getitem__‘, ‘__getnewargs__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__mod__‘, ‘__mul__‘, ‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘,‘__rmod__‘, ‘__rmul__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘capitalize‘, ‘casefold‘, ‘center‘, ‘count‘, ‘encode‘, ‘endswith‘, ‘expandtabs‘, ‘find‘, ‘format‘, ‘format_map‘, ‘index‘, ‘isalnum‘, ‘isalpha‘, ‘isdecimal‘, ‘isdigit‘, ‘isidentifier‘, ‘islower‘, ‘isnumeric‘, ‘isprintable‘, ‘isspace‘, ‘istitle‘, ‘isupper‘, ‘join‘, ‘ljust‘, ‘lower‘, ‘lstrip‘, ‘maketrans‘, ‘partition‘, ‘replace‘, ‘rfind‘, ‘rindex‘, ‘rjust‘, ‘rpartition‘, ‘rsplit‘, ‘rstrip‘, ‘split‘, ‘splitlines‘, ‘startswith‘, ‘strip‘, ‘swapcase‘, ‘title‘, ‘translate‘, ‘upper‘, ‘zfill‘]
我们发现在字符串中可以找到__iter__. 继续看?下list, tuple, dict, set
print(dir(tuple))
print(dir(list))
print(dir(open("护?少妇嫩模.txt"))) # ?件对象
print(dir(set))
print(dir(dict))
结果:
[‘__add__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__dir__‘,
‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘,
‘__getitem__‘, ‘__getnewargs__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘,
‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__mul__‘,
‘__ne__‘, ‘__new__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__rmul__‘,
‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘count‘,
‘index‘]
[‘__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‘]
[‘_CHUNK_SIZE‘, ‘__class__‘, ‘__del__‘, ‘__delattr__‘, ‘__dict__‘,
‘__dir__‘, ‘__doc__‘, ‘__enter__‘, ‘__eq__‘, ‘__exit__‘, ‘__format__‘,
‘__ge__‘, ‘__getattribute__‘, ‘__getstate__‘, ‘__gt__‘, ‘__hash__‘,
‘__init__‘, ‘__init_subclass__‘, ‘__iter__‘, ‘__le__‘, ‘__lt__‘, ‘__ne__‘,
‘__new__‘, ‘__next__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘,
‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘_checkClosed‘,
‘_checkReadable‘, ‘_checkSeekable‘, ‘_checkWritable‘, ‘_finalizing‘,
‘buffer‘, ‘close‘, ‘closed‘, ‘detach‘, ‘encoding‘, ‘errors‘, ‘fileno‘,
‘flush‘, ‘isatty‘, ‘line_buffering‘, ‘mode‘, ‘name‘, ‘newlines‘, ‘read‘,
‘readable‘, ‘readline‘, ‘readlines‘, ‘seek‘, ‘seekable‘, ‘tell‘,
‘truncate‘, ‘writable‘, ‘write‘, ‘writelines‘]
[‘__and__‘, ‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__dir__‘,
‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__gt__‘,
‘__hash__‘, ‘__iand__‘, ‘__init__‘, ‘__init_subclass__‘, ‘__ior__‘,
‘__isub__‘, ‘__iter__‘, ‘__ixor__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘,
‘__ne__‘, ‘__new__‘, ‘__or__‘, ‘__rand__‘, ‘__reduce__‘, ‘__reduce_ex__‘,
‘__repr__‘, ‘__ror__‘, ‘__rsub__‘, ‘__rxor__‘, ‘__setattr__‘, ‘__sizeof__‘,
‘__str__‘, ‘__sub__‘, ‘__subclasshook__‘, ‘__xor__‘, ‘add‘, ‘clear‘,‘copy‘,
‘difference‘, ‘difference_update‘, ‘discard‘, ‘intersection‘,
‘intersection_update‘, ‘isdisjoint‘, ‘issubset‘, ‘issuperset‘, ‘pop‘,
‘remove‘, ‘symmetric_difference‘, ‘symmetric_difference_update‘, ‘union‘,
‘update‘]
[‘__class__‘, ‘__contains__‘, ‘__delattr__‘, ‘__delitem__‘, ‘__dir__‘,
‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘,
‘__getitem__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__init_subclass__‘,
‘__iter__‘, ‘__le__‘, ‘__len__‘, ‘__lt__‘, ‘__ne__‘, ‘__new__‘,
‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__setitem__‘,
‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘clear‘, ‘copy‘, ‘fromkeys‘,
‘get‘, ‘items‘, ‘keys‘, ‘pop‘, ‘popitem‘, ‘setdefault‘, ‘update‘, ‘values‘]
我们发现这?个可以进?for循环的东?都有__iter__函数, 包括range也有. 可以??试?
下.
综上. 我们可以确定. 如果对象中有__iter__函数. 那么我们认为这个对象遵守了可迭代协议.
就可以进?迭代. 这?的__iter__是帮助我们获取到对象的迭代器. 我们使?__next__()来获取
到?个迭代器中的元素. 那么我们之前讲的for的?作原理到底是什么? 继续看代码
s = "我爱北京天安?" c = s.__iter__() # 获取迭代器 print(c.__next__()) # 使?迭代器进?迭代. 获取?个元素 我 print(c.__next__()) # 爱 print(c.__next__()) # 北 print(c.__next__()) # 京 print(c.__next__()) # 天 print(c.__next__()) # 安 print(c.__next__()) # ? print(c.__next__()) # StopIteration
我们可以把要迭代的内容当成?弹. 然后呢. 获取到迭代器__iter__(), 就把?弹都装在弹夹
中. 然后发射就是__next__()把每?个?弹(元素)打出来. 也就是说, for循环的时候. ?开始的
时候是__iter__()来获取迭代器. 后?每次获取元素都是通过__next__()来完成的. 当程序遇到
StopIteration将结束循环
?. ?成器
什么是?成器. ?成器实质就是迭代器.
在python中有三种?式来获取?成器:
1. 通过?成器函数
2. 通过各种推导式来实现?成器
3. 通过数据的转换也可以获取?成器
标签：arm span isl 协议 eof tle ali tty enc
原文地址：https://www.cnblogs.com/liuye1990/p/9197877.html
