14.dict的操作

1.定义

在{}内用逗号分隔开多元素，每一个元素都是key:value的形式，其中value可以是任意类型，而key则必须是不可变类型，通常key应该是str类型，因为str类型会对value有描述性的功能

info={'name':'tony','age':18,'sex':'male'}
info=dict(name='tony',age=18,sex='male') # info={'age': 18, 'sex': 'male', 'name': 'tony'}

2.类型转换

• 列表对应数量元素

>>> info=dict([['name','tony'],('age',18)])
>>> info
{'age': 18, 'name': 'tony'}

• fromkeys会从元组中取出每个值当做key，然后与None组成key:value放到字典中

>>> {}.fromkeys(('name','age','sex'),None)  
{'age': None, 'sex': None, 'name': None}

3.字典的操作

• 按key存取，可存可取

  • 取

  dic = {
      'name': 'xxx',
      'age': 18,
      'hobbies': ['play game', 'basketball']
   }
  print(dic['name'])
  print(dic['hobbies'][1])
  
  xxx
  basketball
  

  • 对于赋值操作，如果key原先不存在于字典，则会新增key:value

  dic['gender'] = 'male'
  print(dic)
  
  {'name': 'xxx', 'age': 18, 'hobbies': ['play game', 'basketball'], 'gender': 'male'}
  

  • 对于赋值操作，如果key原先存在于字典，则会修改对应value的值

  dic['name'] = 'tony'
  
  {'name': 'tony', 'age': 18, 'hobbies': ['play game', 'basketball']}
  

• 长度len

  print(len(dic))
  
  3
  

• 成员运算

  res ='name' in dic
  print(res)
  
  True
  

• 删除

  >>> dic.pop('name')  # 通过指定字典的key来删除字典的键值对
  >>> dic
  {'age': 18, 'hobbies': ['play game', 'basketball']}
  

• 键keys()，值values()，键值对items()

  dic = {'age': 18, 'hobbies': ['play game', 'basketball'], 'name': 'xxx'}
  

  • 获取字典所有的key

  >>> dic.keys()  
  dict_keys(['name', 'age', 'hobbies'])
  

  • 获取字典所有的value

  >>> dic.values()
  dict_values(['xxx', 18, ['play game', 'basketball']])
  

  • 获取字典所有的键值对

  dic.items()
  dict_items([('name', 'xxx'), ('age', 18), ('hobbies', ['play game', 'basketball'])])
  

• 循环

  • 默认遍历的是字典的key

  >>> for key in dic:
  ...     print(key)
  ... 
  age
  hobbies
  name
  

  • 只遍历key

  >>> for key in dic.keys():
  ...     print(key)
  ... 
  age
  hobbies
  name
  

  • 只遍历value

  >>> for key in dic.values():
  ...     print(key)
  ... 
  18
  ['play game', 'basketball']
  xxx
  

  • 遍历key与value

  >>> for key in dic.items():
  ...     print(key)
  ... 
  ('age', 18)
  ('hobbies', ['play game', 'basketball'])
  ('name', 'xxx')
  

4.字典的进阶

• get()

  >>> dic= {'k1':'jason','k2':'Tony','k3':'JY'}
  >>> dic.get('k1')
  'jason'  # key存在，则获取key对应的value值
  >>> res=dic.get('xxx') # key不存在，不会报错而是默认返回None
  >>> print(res)
  None  
  >>> res=dic.get('xxx',666) # key不存在时，可以设置默认返回的值
  >>> print(res)
  666 
  # ps:字典取值建议使用get方法
  

• pop()

  >>> dic= {'k1':'jason','k2':'Tony','k3':'JY'}
  >>> v = dic.pop('k2')  # 删除指定的key对应的键值对,并返回值
  >>> dic
  {'k1': 'jason', 'kk2': 'JY'}
  >>> v
  'Tony'
  

• popitem()

  >>> dic= {'k1':'jason','k2':'Tony','k3':'JY'}
  >>> item = dic.popitem()  # 随机删除一组键值对,并将删除的键值放到元组内返回
  >>> dic
  {'k3': 'JY', 'k2': 'Tony'}
  >>> item
  ('k1', 'jason')
  

• update()

  # 用新字典更新旧字典，有则修改，无则添加
  >>> dic= {'k1':'jason','k2':'Tony','k3':'JY'}
  >>> dic.update({'k1':'JN','k4':'xxx'})
  >>> dic
  {'k1': 'JN', 'k3': 'JY', 'k2': 'Tony', 'k4': 'xxx'}
  

• fromkeys()

  >>> dic = dict.fromkeys(['k1','k2','k3'],[])
  >>> dic
  {'k1': [], 'k2': [], 'k3': []}
  

• setdefault()

  # key存在则不做任何修改，并返回已存在key对应的value值
  >>> dic={'k1':111,'k2':222}
  >>> res=dic.setdefault('k1',666)
  >>> res
  111
  >>> dic # 字典不变
  {'k1': 111, 'k2': 222}