python手记（7）------字典（操作方法）

1.dict方法概述

In[70]: dir(dict)
Out[69]: 

[‘__class__‘,
 ‘__contains__‘,
 ‘__delattr__‘,
 ‘__delitem__‘,
 ‘__dir__‘,
 ‘__doc__‘,
 ‘__eq__‘,
 ‘__format__‘,
 ‘__ge__‘,
 ‘__getattribute__‘,
 ‘__getitem__‘,
 ‘__gt__‘,
 ‘__hash__‘,
 ‘__init__‘,
 ‘__init_subclass__‘,
 ‘__iter__‘,
 ‘__le__‘,
 ‘__len__‘,
 ‘__lt__‘,
 ‘__ne__‘,
 ‘__new__‘,
 ‘__reduce__‘,
 ‘__reduce_ex__‘,
 ‘__repr__‘,
 ‘__setattr__‘,
 ‘__setitem__‘,
 ‘__sizeof__‘,
 ‘__str__‘,
 ‘__subclasshook__‘,
 ‘clear‘,
 ‘copy‘,
 ‘fromkeys‘,
 ‘get‘,
 ‘items‘,
 ‘keys‘,
 ‘pop‘,
 ‘popitem‘,
 ‘setdefault‘,
 ‘update‘,
 ‘values‘]

2.copy()：

　　dict.copy()——返回一个新的（浅拷贝）——列表这类复杂数据需要深拷贝。。

3.clear()

　　　清空字典中所有元素 同 b={}

In[86]: b
Out[85]:
{‘age‘: 26, ‘name‘: ‘ddd‘, ‘university‘: ‘shanghaicaijing‘}
In[87]: b.clear()
In[88]: b
Out[87]:
{}
In[89]: b={}

4.items,keys,values

　　分别返回字典中的类似集合类对象。有迭代行，用来遍历方便。

In[91]: city2
Out[90]: 

{‘fifth‘: [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘],
 ‘first‘: ‘beijing‘,
 ‘forth‘: ‘shenzhen‘,
 ‘second‘: ‘shanghai‘}
In[92]: city2.items()
Out[91]:
dict_items([(‘first‘, ‘beijing‘), (‘second‘, ‘shanghai‘), (‘forth‘, ‘shenzhen‘), (‘fifth‘, [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘])])
In[93]: city2.keys()
Out[92]:
dict_keys([‘first‘, ‘second‘, ‘forth‘, ‘fifth‘])
In[94]: city2.values()
Out[93]:
dict_values([‘beijing‘, ‘shanghai‘, ‘shenzhen‘, [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘]])
In[95]: for i in city2.keys():
...     print(i)
...
first
second
forth
fifth

5.删除方法——pop() & popitem()

　　pop()——删除该键值对，并返回值。如果没有该键，可以返回信息或报错。

In[96]: city
Out[95]:
{‘first‘: ‘beijing‘, ‘second‘: ‘shanghai‘}
In[97]: city.pop(‘third‘,‘未有{0}项‘.format(‘third‘))
Out[96]:
‘未有third项‘
In[98]: city.pop(‘first‘)
Out[97]:
‘beijing‘

　popitem()————随机删除，无需参数，返回类型为数组，空数组报错。

In[99]: help(dict.popitem)
Help on method_descriptor:

popitem(...)
    D.popitem() -> (k, v), remove and return some (key, value) pair as a
    2-tuple; but raise KeyError if D is empty.

In[102]: city3
Out[101]: 

{‘fifth‘: [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘],
 ‘first‘: ‘beijing‘,
 ‘forth‘: ‘shenzhen‘,
 ‘second‘: ‘shanghai‘}
In[103]: city3.popitem()
Out[102]:
(‘fifth‘, [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘])
In[104]: city3.clear()
In[105]: city3.popitem()
Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2881, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-104-c47179c00790>", line 1, in <module>
    city3.popitem()
KeyError: ‘popitem(): dictionary is empty‘

6. 更新字典——update()

In[107]: help(dict.update)
Help on method_descriptor:

update(...)
    D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
    If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
    If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
    In either case, this is followed by: for k in F:  D[k] = F[k]

　　  dict.update(可迭代对象/字典2)————无返回值，增加字典2中的内容到字典中

In[108]: a
Out[107]:
{‘age‘: 26, ‘name‘: ‘eric‘, ‘number‘: ‘201521234‘, ‘university‘: ‘CUP‘}
In[109]: city2
Out[108]: 

{‘fifth‘: [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘],
 ‘first‘: ‘beijing‘,
 ‘forth‘: ‘shenzhen‘,
 ‘second‘: ‘shanghai‘}
In[110]: a.update(city2)
In[111]: a
Out[110]: 

{‘age‘: 26,
 ‘fifth‘: [‘zhengzhou‘, ‘hefei‘, ‘wuhan‘],
 ‘first‘: ‘beijing‘,
 ‘forth‘: ‘shenzhen‘,
 ‘name‘: ‘eric‘,
 ‘number‘: ‘201521234‘,
 ‘second‘: ‘shanghai‘,
 ‘university‘: ‘CUP‘}