python学习笔记18：字典dict

使用help(dict)获取完整方法列表；

字典赋值

>>> addr_book = {‘Swa’:’swa@123.com’, ’Larry’:’larry@124.com’ ,’Mat’:’mat@125.com’,’Spa’:’spa@126.com’}  

获取key对应的value

>>> addr_book[‘Swa’] # 返回值为key对应的value  
‘swa@123.com’  
>>> addr_book.get(‘xxx’, -1) #使用get()，-1是指定（在key不存在时）的返回值  
-1  
  
添加一对key:value:  
```python
>>> addr_book[‘Gui’] = ‘gui@127.com’  

删除一对key:value

>>> addr_book.pop(‘Spa’) # 返回值为value  
‘spa@126.com’  

获取字典的k:v对数/key的个数

>>> len(addr_book)  
4  

添加多对key:value:

>>> addr_book.update({k0:v0, k1:v1})
>>> 

遍历字典：

>>> # 迭代dict中的k-v对
>>> for name, addr in addr_book.items():   
...     print ‘%s : %s’%(name, addr)  
...  
>>> # 迭代dict中的key, 也可以用addr_book.keys()
>>> for name in addr_book:
...     addr = addr_bood[name]  
...     print ‘%s : %s’%(name, addr)  
...  
>>> # 迭代 dict中的value  
>>> for addr in addr_book.values():
...     print ‘%s’%( addr)  
...  

判断key是否存在:

>>> ‘Swa’ in addr_book  
True  

字典中的key是无序的，如果需要key有序，可以使用collections.OrderedDict()
对dict的操作都可以用在OrderedDict上

>>> import collections
>>> d0 = collections.OrderedDict()
>>> d0['a'] = 0
>>> d0['c'] = 2
>>> d0['b'] = 1
>>> d0['d'] = 3
>>> d0
OrderedDict([('a', 0), ('c', 2), ('b', 1), ('d', 3)])
>>>