Python字典方法

0x01 clear

clear方法清除字典中所有的项。这是一个原地操作，无返回值

1 >>> d = {}
2 >>> d[‘name‘] = ‘Gumby‘
3 >>> d[‘age‘] = 13
4 >>> d
5 {‘age‘: 13, ‘name‘: ‘Gumby‘}
6 >>> value = d.clear
7 >>> print value
8 <built-in method clear of dict object at 0x7f8f905c37f8>

0x02 get

get(key[, default])

get方法是一个更宽松的访问字典项的方法。一般来说，如果试图访问字典中不存在的项时会出错，而用get就不会，当访问的项不存在时，还可以自定义默认值

1 >>> d = {}
2 >>> d[‘name‘]
3 Traceback (most recent call last):
4   File "<stdin>", line 1, in <module>
5 KeyError: ‘name‘
6 >>> print d.get(‘name‘)
7 None
8 >>> print d.get(‘name‘, ‘default_value‘)
9 default_value

get方法也可以用来做一些统计之类的，比如统计每个字符有多少个

 1 #!/usr/bin/env python
 2 # coding=utf-8
 3
 4 str = ‘‘‘
 5 aaaaaaaaaaaaaa
 6 bbbbbbbbbbbbb
 7 cccccccccccccccc
 8 dddddddddddddd
 9 33333333333
10 44444444444
11 ``````````````
12 ‘‘‘
13
14 counts = {}
15
16 for c in str:
17     counts[c] = counts.get(c, 0) + 1
18
19 print counts
20
21 """
22 {‘a‘: 14, ‘`‘: 14, ‘c‘: 16, ‘b‘: 13, ‘d‘: 14, ‘\n‘: 8, ‘3‘: 11, ‘4‘: 11}
23 """