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字典

 　　python中，字典还是一些列的键-值对。每个键都与一个值相关联。键是不可变类型也不能重复，值可以是任意类型，可以将任何python对象用作字典中的值。

        键值之间用冒号隔开，键值对之间用逗号隔开。在字典中你存储多少个键值对都可以

         sample:

dict_sample = {"name": "甲壳虫~~~", "age": "18"}

创建字典

赋值创建，函数创建

•  创建空字典
  

   person1_info = {}

• 创建简单单值字典

  person2_info = {"name": "甲壳虫"， "age": "18"}

   

• 创建 多个键值对
  

  person2_info = {"name": "甲壳虫"， 
                           "age": 18，
                           "sex": "男"，
                           "garde": "七年级"，
                           "addr":["中国"，"江苏省"， "南京市"]，
                           ""friends": {"name1": "Jack", "name2": "Merry"}
  
                         }      

• dict函数
  

  print(dict([()]))
  """
   |  dict() -> new empty dictionary
   |  dict(mapping) -> new dictionary initialized from a mapping object's
   |      (key, value) pairs
   |  dict(iterable) -> new dictionary initialized as if via:
   |      d = {}
   |      for k, v in iterable:
   |          d[k] = v
   |  dict(**kwargs) -> new dictionary initialized with the name=value pairs
   |      in the keyword argument list.  For example:  dict(one=1, two=2)
   下面还有很多。。。仅仅截取这些
  """

   

     
• 创建空字典
  

  print(dict()) #{}

• 创建多个键值对
  

  #（iterable，可迭代对象）
  cattle = [("name", "甲壳虫~~~"), ("age", 18), ("sex", "男")]
  print(dict(cattle))#{'name': '甲壳虫~~~', 'age': 18, 'sex': '男'}
  peach = [["name", "桃子"], ["age", 16], ["sex", "女"]]
  print(dict(peach))#{'name': '桃子', 'age': 16, 'sex': '女'}

   

• 指定关键字创建字典
  

  1 baby = dict(name="Little Baby", sex="男")
  2 print(baby, '~~~', type(baby))#{'name': 'Little Baby', 'sex': '男'} ~~~ <class 'dict'>

   

• zip()
  

  zip_data = zip(("name", "age", "sex"), ("peach", 16, "girl"))
  print(dict(zip_data))#{'name': 'peach', 'age': 16, 'sex': 'girl'}

   

 使用字典

字典是键值对形式存在字典中。键和值是一种映射关系。

获取字典中的，值，键和值;

• 通过key查询value，如果键不存在怎抛出异常
  

  dic = {"name": "甲壳虫", "age": 18}
  print(dic['name'])#甲壳虫
  print(dic["sex"])#KeyError: 'sex'

   

• 添加键值对
  

  dic = {"name": "甲壳虫", "age": 18}
  dic['sex'] = '男'
  print(dic)#{'name': '甲壳虫', 'age': 18, 'sex': '男'}

   

• 删除键值对
  

  dic = {"name": "甲壳虫", "age": 18}
  dic['sex'] = '男'
  del dic["age"]
  print(dic)#{'name': '甲壳虫', 'sex': '男'}

   

• 修改键值对
  

  dic = {"name": "甲壳虫", "age": 18}
  dic['sex'] = '女'
  print(dic)#{'name': '甲壳虫', 'age': 18, 'sex': '女'}

   

• 判断字典中是否有对应的键
  

  dic = {"name": "甲壳虫", "age": 18}
  key_in = "name" in dic
  print(key_in)#True
  key_not_in = 'sex' in dic
  print(key_not_in)#False

   

• 判断字典中是否有对应的值
  

  dic = {"name": "甲壳虫", "age": 18}
  value_in = "甲壳虫" in dic["name"]
  print(value_in)

   其实还是根据键，获取到对应的值，然后在去测试是否在字典中（in ， not in ）

• 字典的方法-->字典也是一个类

• clear()方法
  

  dic = {"name": "甲壳虫", "age": 18}
  """ D.clear() -> None.  Remove all items from D. """
  a = dic.clear()
  print(a)#None

   

• get()方法
  

  dic = {"name": "甲壳虫", "age": 18}
  """ Return the value for key if key is in the dictionary, else default.None"""
  print(dic.get("name", "这个默认值是否返回"))#甲壳虫
  
  print(dic.get("sex", "键不在字典中，这里返回了此处设置的默认值"))#键不在字典中，这里返回了此处设置的默认值

   

• update（）
  

  dic = {"name": "甲壳虫", "age": 18}
  """ 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]"""
  dic.update({"name": "peach"})#键存在 更新键所对应的值
  print(dic)#{'name': 'peach', 'age': 18}
  dic.update({"friend": "peach"})#不键存在 ，添加新的键值对
  print(dic)#{'name': 'peach', 'age': 18, 'friend': 'peach'}

   

• setdefault
  

   1 dic = {"name": "甲壳虫", "age": 18}
   2 """ Insert key with a value of default if key is not in the dictionary.
   3     Return the value for key if key is in the dictionary, else default.
   4 None"""
   5 """如果键不在字典中，向字典中添加对应的键值对；并返回默认值
   6    如果键在字典中，直接返回默认的值
   7 """
   8 print(dic.setdefault("age", None))#键在字典中，返回键所对应的值
   9 print(dic)#{'name': '甲壳虫', 'age': 18}
  10 print(dic.setdefault("friend", "键不在字典中"))#键不在字典中,返回设置的值：键不在字典中
  11 print(dic)#字典中添加了新的键值对{'name': '甲壳虫', 'age': 18, 'friend': '键不在字典中'}

   

• pop()
  

  dic = {"name": "甲壳虫", "age": 18}
  """ D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
      If key is not found, default is returned if given, otherwise KeyError is raised
  None"""
  
  print(dic.pop("name"))#甲壳虫
  print(dic)#{'age': 18}

   

• popeitem()
  

  dic = {"name": "甲壳虫", "age": 18}
  """ D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
      If key is not found, default is returned if given, otherwise KeyError is raised
  None"""
  
  print(dic.popitem())#('age', 18)
  print(dic)#{'name': '甲壳虫'}

   

• fromkeys()
  

  """fromkeys(iterable, value=None, /) method of builtins.type instance
      Create a new dictionary with keys from iterable and values set to value.
  None"""
  lst = ["name-1", "name-2"]
  dict_tester = dict(dict.fromkeys(lst))
  print(dict_tester)#{'name-1': None, 'name-2': None}
  tup = ("name-1", "name-2")
  print(dict.fromkeys(tup))#{'name-1': None, 'name-2': None}
  print(dict.fromkeys(["name-1", "name-2", "姓名"]))#{'name-1': None, 'name-2': None, '姓名': None}

   

• keys(),values(),item()

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