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