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

巴特西

python iteration 迭代

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