python iteration 迭代

可迭代的类型：list，tuple，dict，str，bytes，bytearray等

一、怎么判断一个对象是否可迭代

 >>> from collections import Iterable
 >>> isinstance([1, 2, 3], Iterable)
 True
 >>> isinstance((1, 2, 3), Iterable)
 True
 >>> isinstance({'one': 1}, Iterable)
 True
 >>> isinstance('abc', Iterable)
 True
 >>> isinstance(b'abc', Iterable)
 True
 >>> isinstance(bytearray('abc', encoding='utf-8'), Iterable)
 True

二、dict的迭代

 >>> d = {'one': 1, 'two': 2}
 >>> for key in d:
 ...     print(key)
 ...
 one
 two
 >>> for value in d.values():
 ...     print(value)
 ...
 1
 2
 >>> for item in d.items():
 ...     print(item)
 ...
 ('one', 1)
 ('two', 2)

三、list迭代索引和元素－－利用Python内置的enumerate函数可以把一个list变成索引-元素对

 >>> l = [1, 2, 3]
 >>> e = enumerate(l)
 >>> e
 <enumerate object at 0x101694558>
 >>> for index, value in e:
 ...     print(index, value)
 ...
 0 1
 1 2
 2 3

四、迭代多个变量

 >>> for x, y in [(1, 1), (2, 4), (3, 9)]:
 ...     print(x, y)
 ...
 1 1
 2 4
 3 9