1.字典的定义
在Python中,字典是一系列键值对,每个键与每个值关联。键必须是唯一的,值不一定。# 表示dic = {"name":"jqdbd","age":6,"sex":"femal"}2.字典的创建
2.1 创建空字典
# 先创建一个空的花括号 =》 空字典dic = {}# 分行添加各个键值对dic["name"] = "jqdbd"dic["age"] = 6dic["sex"] = "femal"print(dic)# 返回{'name': 'jqdbd', 'age': 6, 'sex': 'femal'}2.2 元组转换为字典
# 先定义一个元组a = (('name',"jqdbd"),('age',6),("sex","femal"))# 将该元组转换成字典dic = dict(a) print(dic)#返回{'name': 'jqdbd', 'age': 6, 'sex': 'femal'}3.字典元素的增加(同新增)
3.1 直接增加键值对
dic = {"name":"jqdbd","age":6}dic["sex"] = "femal"print(dic)# 返回{'name': 'jqdbd', 'age': 6, 'sex': 'femal'}3.2 dic.setdefault
# dic.setdefault 原先字典中有键值对则不做任何改变,没有就添加dic = {"name":"jqdbd","age":6}dic["sex"] = "femal"print(dic)dic.setdefault('weght',150)print("第一次调用:",dic)dic.setdefault("weght",12)print("第二次调用",dic)# 返回{'name': 'jqdbd', 'age': 6, 'sex': 'femal'}第一次调用: {'name': 'jqdbd', 'age': 6, 'sex': 'femal', 'weght': 150}第二次调用 {'name': 'jqdbd', 'age': 6, 'sex': 'femal', 'weght': 150}3.3 dic.update
# updatedic = {"name":"jqdbd","age":6,"sex":"femal"}dic.update({"mother":"小沈"})print(dic)# 返回{'name': 'jqdbd', 'age': 6, 'sex': 'femal', 'weght': 150, 'mother': '小沈'}4.字典元素的查找(遍历)
4.1 dic.get(key,0)
如果使用dic[key]的方式查找值,key不存在会报错:KeyError,用dic.get(key,0)访问,key不存在则返回0 dic = {"name":"jqdbd","age":6}# 查找不存在的键值对print(dic.get("sex",0))# 返回0# 查找存在的键值对print(dic.get("name",0))# 返回jqdbd4.2 dic.items()
遍历所有键值对
items = dic.items()print(items)print(type(items))# 返回dict_items([('name', 'jqdbd'), ('age', 6)])<class 'dict_items'>for key,vlaue in items: print("Key",key) print("Value",vlaue)# 返回Key nameValue jqdbdKey ageValue 6# 以列表形式返回key_vlaue_list = [[key,vlaue] for key,vlaue in items]print(key_vlaue_list)# 返回[['name', 'jqdbd'], ['age', 6]]4.3 dic.keys()
遍历字典所有键
dic = {"name":"jqdbd","age":6}keys = dic.keys()key = [key for key in keys]print(key)# 返回['name', 'age']# 按顺序遍历所有键sorted_key = [key for key in sorted(keys)]print(sorted_key)# 返回['age', 'name']4.4 dic.values()
遍历字典所有值
values = dic.values()print(values)# 去掉重复的值value = [value for value in set(values)]print(value)# 返回dict_values(['jqdbd', 6, 'jqdbd'])['jqdbd', 6]5. 字典元素的删除
5.1 dic.pop(key)
返回相应的键,同时删除该键值对
# dic.pop(key)dic = {"name":"jqdbd","age":6,"mother":"jqdbd"}print(dic.pop("mother"))print(dic)# 返回jqdbd{'name': 'jqdbd', 'age': 6}5.2 dic.popitem()
默认删除最后一组键值对
dic = {"name":"jqdbd","age":6,"mother":"jqdbd"}print(dic.popitem())print(dic)# 返回('mother', 'jqdbd'){'name': 'jqdbd', 'age': 6}5.3 del dic[key]
没有返回值,同时删除该键值对
# del dic[key]dic = {"name":"jqdbd","age":6,"mother":"jqdbd"}del dic["mother"]print(dic)# 返回{'name': 'jqdbd', 'age': 6}5.4 del dic
直接删除字典对象,打印字典会报错
dic = {"name":"jqdbd","age":6,"mother":"jqdbd"}del dicprint(dic)# 返回NameError: name 'dic' is not defined5.5 dic.clear()
清空字典,打印字典返回一个空字典
dic = {"name":"jqdbd","age":6,"mother":"jqdbd"}dic.clear()print(dic)# 返回{}