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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":"妮妮","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"] = "妮妮" dic["age"] = 6 dic["sex"] = "femal" print(dic) # 返回 {'name': '妮妮', 'age': 6, 'sex': 'femal'}2.2 元组转换为字典 # 先定义一个元组 a = (('name',"妮妮"),('age',6),("sex","femal")) # 将该元组转换成字典 dic = dict(a) print(dic) #返回 {'name': '妮妮', '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":"妮妮","age":6} dic["sex"] = "femal" print(dic) # 返回 {'name': '妮妮', '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":"妮妮","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': '妮妮', 'age': 6, 'sex': 'femal'} 第一次调用: {'name': '妮妮', 'age': 6, 'sex': 'femal', 'weght': 150} 第二次调用 {'name': '妮妮', 'age': 6, 'sex': 'femal', 'weght': 150}3.3 dic.update # update dic = {"name":"妮妮","age":6,"sex":"femal"} dic.update({"mother":"小沈"}) print(dic) # 返回 {'name': '妮妮', '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":"妮妮","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 妮妮4.2 dic.items() 遍历所有键值对 items = dic.items() print(items) print(type(items)) # 返回 dict_items([('name', '妮妮'), ('age', 6)]) for key,vlaue in items: print("Key",key) print("Value",vlaue) # 返回 Key name Value 妮妮 Key age Value 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', '妮妮'], ['age', 6]]4.3 dic.keys() 遍历字典所有键 dic = {"name":"妮妮","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(['妮妮', 6, '妮妮']) ['妮妮', 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":"妮妮","age":6,"mother":"妮妮"} print(dic.pop("mother")) print(dic) # 返回 妮妮 {'name': '妮妮', 'age': 6}5.2 dic.popitem() 默认删除最后一组键值对 dic = {"name":"妮妮","age":6,"mother":"妮妮"} print(dic.popitem()) print(dic) # 返回 ('mother', '妮妮') {'name': '妮妮', '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":"妮妮","age":6,"mother":"妮妮"} del dic["mother"] print(dic) # 返回 {'name': '妮妮', 'age': 6}5.4 del dic 直接删除字典对象,打印字典会报错 dic = {"name":"妮妮","age":6,"mother":"妮妮"} del dic print(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":"妮妮","age":6,"mother":"妮妮"} dic.clear() print(dic) # 返回 {}
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