python 字典dict
目录
字典
字典方法
案例
字典(dict)
1.记录多个值,key是用来描述value的特征
2.定义
在{}内有多个key:value值,用逗号分开,
# value可以是任意数据类型,key必须是不可变类型,通常情况下为字符串
# a = {'name':'jason','password':123}
# a = dict({'name':'jason','password':123})
# print(a,type(a))
# print(a['name'])
# print(a['password'])
3.用法
# 用法一 # a = dict(x =1,y = 2,z = 3) # print(a) # {'x': 1, 'y': 2, 'z': 3} # 用法二 # userinfo = [ # ['name','jason'], # ['age',18], # ['sex','male'] # ] # d = {} # for k,v in userinfo: # d[k]=v # print(d) # {'name': 'jason', 'age': 18, 'sex': 'male'}
字典方法
1.按key取值,可取可换,则有序的
# a = {'name':'jason','password':223} # print(a['name']) # print(a['password']) # a['name'] = 'egon' # print(a) # a['password'] = 123 # print(a)
2.长度len():统计的是key:value的个数
# a = {'name':'jason','password':123} # # print(a) # # print(len(a))
3.成员运算in和not in
字典中成员运算判读的是key
# a = {'name':'jason','password':123} # print('name' in a) # True # print(123 in a) # False
4.删除
# a = {'name':'jason','password':123} # 通用的del:删除整个key:value键值对 # del a['name'] # print(a) # del a['age'] # print(a) # 不存在报错 # pop 删除的key对应的值,返回value值.应该叫弹出 # a = {'name':'jason','password':123} # res = a.pop('name') # print(res) # jason # print(a) # popitem 删除的是后面的key:value.应该叫弹出 # a = {'name':'jason','password':123} # res = a.popitem() # print(res) # print(a)
5.键keys(),值values(),键值对iiems()
注意:在Python2 和Python3的区别
在Python2中是列表,在Python3中是元组
# dic = {'name':'egon','age':18} # print(dic.keys()) # print(dic.values()) # print(dic.items()) # dict_keys(['name', 'age']) # dict_values(['egon', 18]) # dict_items([('name', 'egon'), ('age', 18)])
6.循环
# dic = {'name':'egon','age':18,'sex':'male'} # for k in dic.keys(): # print(k,dic[k]) # name egon # age 18 # sex male
7.get() 和按key取值比较就是不报错
# dic = {'name':'egon','age':123,'sex':'male'} # # dic['aaa'] # 报错 # # v = dic.get('name') # # print(v) # # # # v = dic.get('sss') # # print(v) # None 不报错
8.总结:
存多个值
无序的
可变