字典(dict):用{}表示,由一组组键值对(key:value)构成,
特点:无序、查询效率高,key必须是不可变类型且唯一
我们可以将字典看成一个大的仓库,一个个键值对就是仓库中的一个个房间,key是房间的门牌号,value是房间中数据。想要拿房间中的数据(value),通过门牌号(key)就行了。
2.字典常用方法切记:字典是一个可变对象,对字典进行修改操作会使原来的字典发生变化
名称 | 作用 |
---|---|
dic[key] = value | 如果key存在,替换掉原来的value,如果没有则将这一键值对加上 |
dic.setdefault(key,value) | 如果key存在则不变,不存在则添加,返回新加的值 |
dic.pop(key) | 删除指定的键值对 |
dic.popitem() | 随机删除,但是我们看到的效果时删除最后一个 |
del dic[key] | 删除指定键值对 |
dic.clear() | 清空字典 |
dic1.update(dic2) | dic1独有的保留下来,dic2独有的添加上去,共有的将dic1的值换成dic2的值 |
dic.get(key,参数) | 获取key对应的值。key存在则返回响应的值,不存在在返回参数,不设置参数则返回None |
dic.keys() | 获取所有的key,结果像list但不是list |
dic.values() | 获取所有的values,结果像list但不是list |
dic.items() | 获取所有的键值对,每一个键值对是一个元组,结果像list但不是list |
dict.fromkeys(a,b) | 这是一个类方法,a为可迭代对象,b为值,将a中的每一个元素与b组成键值对 |
具体看代码:
dic = {"a":1,"b":2}
dic["c"] = 5
print(dic) 结果是:{'a': 1, 'b': 2, 'c': 5}
dic = {"a":1,"b":2}
dic["a"] = 4
print(dic) 结果是:{'a': 4, 'b': 2}
dic = {"a":1,"b":2}
c = dic.setdefault("c",4)
print(dic) 结果是:{'a': 1, 'b': 2, 'c': 4}
print(c) 结果是:4
dic = {"a":1,"b":2}
dic.setdefault("a",4)
print(dic) 结果是:{'a': 1, 'b': 2}
dic = {"a":1,"b":2}
dic.pop("a")
print(dic) 结果是:{'b': 2}
dic = {"a":1,"b":2,"c":3,"d":4}
dic.popitem()
print(dic) 结果是:{'a': 1, 'b': 2, 'c': 3}
dic = {"a":1,"b":2,"c":3,"d":4}
del dic["a"]
print(dic) 结果是:{'b': 2, 'c': 3, 'd': 4}
dic = {"a":1,"b":2,"c":3,"d":4}
dic.clear()
print(dic) 结果是:{}
dic1 = {"a":1,"b":2,"c":3,"d":4}
dic2 = {"e":5,"f":6,"g":7,"d":5}
dic1.update(dic2)
print(dic1) 结果是:{'a': 1, 'b': 2, 'c': 3, 'd': 5, 'e': 5, 'f': 6, 'g': 7}
dic1 = {"a":1,"b":2,"c":3,"d":4}
print(dic1.get("a",5)) 结果是:1
print(dic1.get("e")) 结果是:None
print(dic1.get("e",7)) 结果是:7
dic1 = {"a":1,"b":2,"c":3,"d":4}
a = dic1.keys()
print(a,type(a)) 结果是:dict_keys(['a', 'b', 'c', 'd'])
dic1 = {"a":1,"b":2,"c":3,"d":4}
a = dic1.values()
print(a,type(a)) 结果是:dict_values([1, 2, 3, 4])
dic1 = {"a":1,"b":2,"c":3,"d":4}
a = dic1.items()
print(a,type(a)) 结果是:dict_items([('a', 1), ('b', 2), ('c', 3), ('d', 4)])
dic = dict.formkeys("123","abc")
print(dic) 结果是:{"1":"a","2":"b","3":"c"}
3.字典的遍历
字典是一个可以迭代对象
1.直接for循环
dic1 = {"a":1,"b":2,"c":3,"d":4}
for key in dic1:
print(key)
print(dic1[key])
print("--")
2.使用keys()或values()方法
dic1 = {"a":1,"b":2,"c":3,"d":4}
for key in dic1.keys():
print(key)
print(dic1[key])
for value in dic1.values():
print(value)
3.使用items()
for key,value in dic1.items():
print(key,value)
杨鸿儒
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