python的6种基本数据类型--字典
字典
字典的定义与特性
字典是Python语言中唯一的映射类型。
定义：｛key1:value1,key2:value2｝
1、键与值用冒号"："分开；2、项与项用逗号"，"分开；
特性：
1.key：value结构2.key必须可hash、且必须为不可变数据类型、必须唯一(数字、字符串、元组)3.value可存放任意多个值、可修改、可以不唯一4.无序
字典的创建与常见操作
字典的创建
# a.直接用 {} 创建，key:value对应
>>> skills = {"s1":"python","s2":"linux","s3":"html/css","s4":"JavaScript"}
>>> skills
{'s1': 'python', 's2': 'linux', 's3': 'html/css', 's4': 'JavaScript'}
# b.用dict转换
>>> skills_1 = dict(s1="python",s2="linux")
>>> skills_1
{'s1': 'python', 's2': 'linux'}
>>> skills_1 = dict("s1"="python","s2"="linux") # 不能这样创建,本身有歧义，前后都是两个字符串
SyntaxError: keyword can't be an expression
# 将本身就是字典转换成dict
>>> skills_2 = dict({"s1":"python","s2":"linux"})
>>> skills_2
{'s1': 'python', 's2': 'linux'}
# 将形如key-value结构的转换为字典
>>> skills_3 = dict((["s1","python"],["s2","linux"]))
>>> skills_3
{'s1': 'python', 's2': 'linux'}
>>> skills_3 = dict([["s1","python"],["s2","linux"]])
>>> skills_3
{'s1': 'python', 's2': 'linux'}
>>> skills_3 = dict([("s1","python"),("s2","linux")])
>>> skills_3
{'s1': 'python', 's2': 'linux'}
# key 为元组的字典
>>> skills_3 = dict([[(1,2),"python"],[(21,21),"linux"]])
>>> skills_3
{(1, 2): 'python', (21, 21): 'linux'}x
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# a.直接用 {} 创建，key:value对应
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>>> skills = {"s1":"python","s2":"linux","s3":"html/css","s4":"JavaScript"}
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>>> skills
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{'s1': 'python', 's2': 'linux', 's3': 'html/css', 's4': 'JavaScript'}
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# b.用dict转换
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>>> skills_1 = dict(s1="python",s2="linux")
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>>> skills_1
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{'s1': 'python', 's2': 'linux'}
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>>> skills_1 = dict("s1"="python","s2"="linux") # 不能这样创建,本身有歧义，前后都是两个字符串
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SyntaxError: keyword can't be an expression
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# 将本身就是字典转换成dict
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>>> skills_2 = dict({"s1":"python","s2":"linux"})
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>>> skills_2
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{'s1': 'python', 's2': 'linux'}
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# 将形如key-value结构的转换为字典
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>>> skills_3 = dict((["s1","python"],["s2","linux"]))
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>>> skills_3
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{'s1': 'python', 's2': 'linux'}
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>>> skills_3 = dict([["s1","python"],["s2","linux"]])
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>>> skills_3
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{'s1': 'python', 's2': 'linux'}
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>>> skills_3 = dict([("s1","python"),("s2","linux")])
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>>> skills_3
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{'s1': 'python', 's2': 'linux'}
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# key 为元组的字典
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>>> skills_3 = dict([[(1,2),"python"],[(21,21),"linux"]])
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>>> skills_3
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{(1, 2): 'python', (21, 21): 'linux'}
字典的常见操作
键、值、键值对
dic.keys() 返回一个包含字典所有KEY的列表；
dic.values() 返回一个包含字典所有value的列表；
dic.items() 返回一个包含所有（键，值）元祖的列表；
>>> skills
{'s1': 'python', 's2': 'linux', 's3': 'html/css', 's4': 'JavaScript'}
>>> skills.keys
<built-in method keys of dict object at 0x00000209A130DCF0>
>>> skills.keys()
dict_keys(['s1', 's2', 's3', 's4'])
>>> skills.values()
dict_values(['python', 'linux', 'html/css', 'JavaScript'])
>>> skills.items()
dict_items([('s1', 'python'), ('s2', 'linux'), ('s3', 'html/css'), ('s4', 'JavaScript')])
新增
dic['new_key'] = 'new_value'
dic.setdefault(key,None) 如果字典中不存在Key键，由 dic[key] = default 为它赋值,这里defalut=None，实际创建需要填value
修改
dic['key'] = 'new_values' 如果key在字典中存在，'new_value'将会替代原来的value值,不存在则创建
dic.update(dic2) 将字典dic2的键值对添加到字典dic中
查看
dic['key'] 返回字典中key对应的值，若key不存在字典中，则报错；
dict.get(key,default = None) 返回字典中key对应的值，若key不存在字典中，则返回default的值（default默认为None）
循环(3)
a. for i in dic.keys() 等同于 for i in dic
>>> for k in skills.keys():print(k)
s1
s2
s3
s4
>>> for k in skills:print(k)
s1
s2
s3
s4
b. for k,v in dic.items()
>>> for k,v in skills.items():print(k,v)
s1 python
s2 linux
s3 docker
s4 JavaScript
c.
>>> for k,v in enumerate(skills):print(k,v)
0 s1
1 s2
2 s3
3 s4
>>> for k,v,j in enumerate(skills):print(k,v,j)
Traceback (most recent call last):
File "<pyshell#48>", line 1, in <module>
for k,v,j in enumerate(skills):print(k,v,j)
ValueError: not enough values to unpack (expected 3, got 2)
长度
len(dic)
x
1
键、值、键值对
2
dic.keys() 返回一个包含字典所有KEY的列表；
3
dic.values() 返回一个包含字典所有value的列表；
4
dic.items() 返回一个包含所有（键，值）元祖的列表；
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>>> skills
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{'s1': 'python', 's2': 'linux', 's3': 'html/css', 's4': 'JavaScript'}
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>>> skills.keys
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<built-in method keys of dict object at 0x00000209A130DCF0>
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>>> skills.keys()
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dict_keys(['s1', 's2', 's3', 's4'])
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>>> skills.values()
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dict_values(['python', 'linux', 'html/css', 'JavaScript'])
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>>> skills.items()
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dict_items([('s1', 'python'), ('s2', 'linux'), ('s3', 'html/css'), ('s4', 'JavaScript')])
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新增
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dic['new_key'] = 'new_value'
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dic.setdefault(key,None) 如果字典中不存在Key键，由 dic[key] = default 为它赋值,这里defalut=None，实际创建需要填value
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修改
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dic['key'] = 'new_values' 如果key在字典中存在，'new_value'将会替代原来的value值,不存在则创建
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dic.update(dic2) 将字典dic2的键值对添加到字典dic中
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查看
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dic['key'] 返回字典中key对应的值，若key不存在字典中，则报错；
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dict.get(key,default = None) 返回字典中key对应的值，若key不存在字典中，则返回default的值（default默认为None）
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循环(3)
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a. for i in dic.keys() 等同于 for i in dic
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>>> for k in skills.keys():print(k)
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s1
35
s2
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s3
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s4
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>>> for k in skills:print(k)
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s1
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s2
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s3
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s4
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b. for k,v in dic.items()
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>>> for k,v in skills.items():print(k,v)
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s1 python
48
s2 linux
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s3 docker
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s4 JavaScript
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c.
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>>> for k,v in enumerate(skills):print(k,v)
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0 s1
55
1 s2
56
2 s3
57
3 s4
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>>> for k,v,j in enumerate(skills):print(k,v,j)
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Traceback (most recent call last):
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File "<pyshell#48>", line 1, in <module>
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for k,v,j in enumerate(skills):print(k,v,j)
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ValueError: not enough values to unpack (expected 3, got 2)
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长度
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len(dic)
68