Python学习笔记6-字典

定义

使用键值对，

>>> person = {"name":"keven","age":15,"gender":"male"}
>>> person[‘name‘]
‘keven‘
>>> type(person)
<type ‘dict‘>

字典可以原地修改，即它是可变的。

>>> dict1={}
>>> id(dict1)
139736380198256
>>> dict1["name"] = "Keven"
>>> id(dict1)
139736380198256
>>> dict1
{‘name‘: ‘Keven‘}

利用元组在建构字典，方法如下：

>>> name = (["first","Google"],["second","Yahoo"])
>>> website = dict(name)
>>> website
{‘second‘: ‘Yahoo‘, ‘first‘: ‘Google‘}

或者用这样的方法：

>>> ad = dict(name="keven", age=42)
>>> ad
{‘age‘: 42, ‘name‘: ‘keven‘

基本操作

• len(d)，返回字典(d)中的键值对的数量

>>> city_code = {‘suzhou‘: ‘0512‘, ‘beijing‘: ‘011‘, ‘shanghai‘: ‘012‘, ‘tangshan‘: ‘0315‘}
>>> len(city_code)
4

• d[key]，返回字典(d)中的键(key)的值

>>> city_code["suzhou"]
‘0512‘

• d[key]=value，将值(value)赋给字典(d)中的键(key)

>>> city_code = {‘suzhou‘: ‘0512‘, ‘beijing‘: ‘011‘, ‘shanghai‘: ‘012‘, ‘tangshan‘: ‘0315‘}
>>> city_code["shenzhen"]="1212"
>>> city_code
{‘suzhou‘: ‘0512‘, ‘beijing‘: ‘011‘, ‘shanghai‘: ‘012‘, ‘tangshan‘: ‘0315‘, ‘shenzhen‘: ‘1212‘}

• del d[key]，删除字典(d)的键(key)项（将该键值对删除）

>>> del city_code["shanghai"]
>>> city_code
{‘suzhou‘: ‘0512‘, ‘beijing‘: ‘011‘, ‘tangshan‘: ‘0315‘, ‘shenzhen‘: ‘1212‘}

• key in d，检查字典(d)中是否含有键为 key 的项

>>> "shenzhen" in city_code
True
>>> "sz" in city_code
False

字典也可以实现格式化字符

>>> city_code = {"suzhou":"0512", "tangshan":"0315", "hangzhou":"0571"}
>>> " Suzhou is a beautiful city, its area code is %(suzhou)s" % city_code
‘ Suzhou is a beautiful city, its area code is 0512