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

 1 >>> from collections import Iterable
 2 >>> isinstance([1, 2, 3], Iterable)
 3 True
 4 >>> isinstance((1, 2, 3), Iterable)
 5 True
 6 >>> isinstance({‘one‘: 1}, Iterable)
 7 True
 8 >>> isinstance(‘abc‘, Iterable)
 9 True
10 >>> isinstance(b‘abc‘, Iterable)
11 True
12 >>> isinstance(bytearray(‘abc‘, encoding=‘utf-8‘), Iterable)
13 True

二、dict的迭代

 1 >>> d = {‘one‘: 1, ‘two‘: 2}
 2 >>> for key in d:
 3 ...     print(key)
 4 ...
 5 one
 6 two
 7 >>> for value in d.values():
 8 ...     print(value)
 9 ...
10 1
11 2
12 >>> for item in d.items():
13 ...     print(item)
14 ...
15 (‘one‘, 1)
16 (‘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

 1 >>> l = [1, 2, 3]
 2 >>> e = enumerate(l)
 3 >>> e
 4 <enumerate object at 0x101694558>
 5 >>> for index, value in e:
 6 ...     print(index, value)
 7 ...
 8 0 1
 9 1 2
10 2 3

四、迭代多个变量

1 >>> for x, y in [(1, 1), (2, 4), (3, 9)]:
2 ...     print(x, y)
3 ...
4 1 1
5 2 4
6 3 9