python dictionary

python dictionary

简介

字典是一个无序的集合

字典有key-value键值对组成

字典中的键不可以重复，key的集合可以看成一个set

操作符

函数

In [15]: d = {"name":"xiaoming","pwd":"123456"}

In [16]: del d["name"]

In [17]: d
Out[17]: {'pwd': '123456'}

In [18]: d["name"] = "xiaoming"

In [19]: d
Out[19]: {'name': 'xiaoming', 'pwd': '123456'}

In [20]: keys = d.keys()

In [21]: keys
Out[21]: ['pwd', 'name']

In [22]: type(keys)
Out[22]: list

In [23]: d.values()
Out[23]: ['123456', 'xiaoming']

In [24]: type(d.values())
Out[24]: list

In [25]: d.items()
Out[25]: [('pwd', '123456'), ('name', 'xiaoming')]

In [26]: d["test"]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-26-b3c970f9eb2a> in <module>()
----> 1 d["test"]

KeyError: 'test'

In [27]: d.get("test")

In [29]: if d.get("test") == None:
....:     print "No this Key"
....:
No this Key

In [30]: d.get("test","No this key")
Out[30]: 'No this key'

可见:

d.keys()，d.values(),d.items()得到的都是list对象

如果key不存在通过k[“key”]来访问会报错，通过k.get()方法返回值为None不会报错。

内置函数算法复杂度