字典相关的函数

字典操作（字典里的键必须是唯一）

dict_1 ={'name':'shenzhen','age':'40','score':'90' }
print (dict_1)

1.往字典中添加键值对

dict["key"] = "value"


dic_1={"fruit":"orange","food":"meat","foods":"orange"}
dic_1["city"]="shenzhen"
print(dic_1)

setdefault（）如果键不已经存在于字典中，将会添加键并将值设为默认值。

dic_1={"fruit":"orange","food":"meat","foods":"orange"}
dic_1.setdefault("name")
print(dic_1)

 #结果{'fruit': 'orange', 'food': 'meat', 'foods': 'orange', 'name': None}

dic_1={"fruit":"orange","food":"meat","foods":"orange"}
dic_1.setdefault("name","shenzhen")
print(dic_1)

#结果{'fruit': 'orange', 'food': 'meat', 'foods': 'orange', 'name': 'shenzhen'}

2.替换字典中指定键的值 dict["key"] = "value"

dic_1={"fruit":"orange","food":"meat","foods":"orange"}
dic_1["fruit"]="apple"
print(dic_1)

3.update（）一个字典所有项追加到另一个字典里

dic_1={"fruit":"orange","food":"meat","foods":"orange"}
dic_2={"country":"china"}
dic_1.update(dic_2)
print(dic_1)
print("新字典：",dic_1)

print(dic_2)

4.字典取值　get（）函数返回指定键的值，如果值不在字典中返回默认值。

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dic_1={"fruit":"orange","food":"meat","foods":"orange"}
print(dic_1.get("fruit"))
print(dic_1.get("name"))#键不存在返回值为None
print("键返回的值是：%s" % dic_1.get("food"))

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":{"guangdong":"shenzhen","guangxi":"nanning"}}
print(dic_1.get("zhongguo"))

5.keys（）从字典中取出所有键，可通过 list() 来转换为列表

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":{"guangdong":"shenzhen","guangxi":"nanning"}}
dic_2=dic_1.keys()
print(dic_2)
print(type(dic_2))

#通过list()方法转换为列表

print(list(dic_2))

6.values（）从字典中取出所有值，可以使用 list() 来转换为列表，列表为字典中的所有值

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}
dic_2=dic_1.values()
print(dic_2)

#通过list()方法转换为列表

list_1=list(dic_2)
print(list_1[3])

7.del 删除键值对

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}
del dic_1["fruit"] #删除对应的键值对
print(dic_1)

#可以通过del 删除整个字典

del dic_1

8.pop（）删除字典给定键 key 所对应的值，返回值为被删除的值。

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}

print(dic_1.pop("fruit"))#返回值为"orange"
print(dic_1)

9.popitem（）随机删除字典的键值对

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}
new_1=dic_1.popitem()

print(type(new_1))#返回值为包含被删除的键值对的一个元组
print(new_1)

print(dic_1)

10.clear（）函数用于删除字典内所有元素，没有返回值。

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}
dic_1.clear()
print(dic_1)

11.copy（）复制创建字典

dic_1={"fruit":"orange","food":"meat","foods":"orange","zhongguo":"guangdong"}
new_dic=dic_1.copy()
print("复制的新字典为：",new_dic)

12.in或not in检查字典是否有指定的键，有结果为 True，没有结果为 False

dic_1={"fruit":"orange","food":"meat","fruits":"orange","zhongguo":"guangdong"}
print("fruit" in  dic_1)

print("foods" not in dic_1)

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