基础篇15-再议数据结构

1. sorted(iterable, key=None, reverse=False)
2. list之sort()方法
3. key最好用

```python
a = ['2354', '1234', '457345', '23']  
a.sort(key = int)  #  结果['23', '1234', '2354', '457345']

a = [('age1', 2), ('age2', 4), ('age3', 1)]
a.sort(key=lambda x:x[1], reverse=True)
```

2. cmp是什么(a>b)-(a<b)，python3中已经删除此方法和参数

```python
cmp(1,2) # -1
cmp(2,2) # 0
cmp(2,1) # 1
```

3. 多级排序咋办

import operator
a = [(2,1,6), (4,8,2), (1,3,9)]
a.sort(key=operator.itemgetter(1,2))   #   [(2, 1, 6), (1, 3, 9), (4, 8, 2)]

a = [(1,2,3), (2,3,4), (0,1,2)]
a.sort(key=operator.itemgetter(1,2))   # 所以这个是以游标1，也就是前面的为主

4. 字典如何去排序