Python基础，day2

Posted 2020-09-13

本节内容

1. 列表、元组操作
2. 字符串操作
3. 字典操作
4. 集合操作
5. 文件操作
6. 字符编码与转码

1. 列表、元组操作

列表是我们以后最常用的数据类型之一，通过列表可以对数据实现最方便的存储、修改等操作

定义列表

name = ["Martin","Annie","JMA","Martin","Ly"]

通过下标访问列表中的元素，下标从0开始计数

1 >>> name[0]
2 ‘Martin‘
3 >>> name[4]
4 ‘Ly‘
5 >>> name[-1]    #可以倒着取
6 ‘Ly‘

切片:取多个元素

>>> name = ["Martin","Annie","JMA","Martin","Ly"]
>>> name[1:4]               #取下标1至下标4之间的数字，包括1，不包括4
[‘Annie‘, ‘JMA‘, ‘Martin‘]
>>> name[0:3]               #取下标0至下标3间的数字，包括0，不包括3
[‘Martin‘, ‘Annie‘, ‘JMA‘]
>>> name[:3]                 #如果是从头开始取，0可以忽略，跟上句效果一样
[‘Martin‘, ‘Annie‘, ‘JMA‘]
>>> name[3:-1]              #取下标3至-1的值，不包括-1
[‘Martin‘]
>>> name[3:]                 #如果想取最后一个，必须不能写-1，只能这么写
[‘Martin‘, ‘Ly‘]
>>> name[0::2]              #后面的2是代表，每隔一个元素，就取一个
[‘Martin‘, ‘JMA‘, ‘Ly‘]
>>> name[::2]                #和上面的效果一样
[‘Martin‘, ‘JMA‘, ‘Ly‘]

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追加

>>> name.append("HZY")
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]

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插入

>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]
>>> name.insert(1,"HZY")
>>> name
[‘Martin‘, ‘HZY‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]

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修改

[‘Martin‘, ‘HZY‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]
>>> name[1] = "acer"
>>> name
[‘Martin‘, ‘acer‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]

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删除

>>> name
[‘Martin‘, ‘acer‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]

>>> del name[1]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘, ‘HZY‘]

>>> name.remove("HZY")    #删除指定元素
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Ly‘]

>>> name.pop()    #删除列表最后一个值
‘Ly‘
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘]

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扩展

>>> name2 = [1,2,3,4]
>>> name.extend(name2)
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, ‘Martin‘, 1, 2, 3, 4]

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拷贝

浅copy,列表的copy
>>> name = ["Martin", "Annie", "JMA", ["ABC", "test"], "Martin"]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘ABC‘, ‘test‘], ‘Martin‘]
>>> name2 = name.copy()
>>> name2
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘ABC‘, ‘test‘], ‘Martin‘]

>>> name[3][0]
‘ABC‘
>>> name[3][0] = "abc"

>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]
>>> name2
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]


浅copy,copy模块的copy
>>> import copy
>>> name3 = copy.copy(name)
>>> name3
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]

>>> name[3][0] = "123"

>>> name3
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘123‘, ‘test‘], ‘Martin‘]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘123‘, ‘test‘], ‘Martin‘]


deepcopy，copy模块的deepcopy,一般别用
>>> import copy
>>> name4 = copy.deepcopy(name)
>>> name4
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘123‘, ‘test‘], ‘Martin‘]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘123‘, ‘test‘], ‘Martin‘]

>>> name[3][0] = "abc"

>>> name4
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘123‘, ‘test‘], ‘Martin‘]
>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]

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统计

>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]
>>> name.count("Martin")
2

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排序&翻转

>>> name
[‘Martin‘, ‘Annie‘, ‘JMA‘, [‘abc‘, ‘test‘], ‘Martin‘]
>>> name.sort()    #排序
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: ‘<‘ not supported between instances of ‘list‘ and ‘str‘     #3.0里不同数据类型不能放在一起排序了

>>> name[3] = "test"
>>> name
[‘Annie‘, ‘JMA‘, ‘Martin‘, ‘test‘, ‘Martin‘]
>>> name.sort()
>>> name
[‘Annie‘, ‘JMA‘, ‘Martin‘, ‘Martin‘, ‘test‘]

>>> name.reverse()    #反转
>>> name
[‘test‘, ‘Martin‘, ‘Martin‘, ‘JMA‘, ‘Annie‘]

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获取下标

>>> name
[‘test‘, ‘Martin‘, ‘Martin‘, ‘JMA‘, ‘Annie‘]
>>> name.index("JMA")
3

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清空列表

name.clear()  #清空列表

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列表循环

for i in name:
     for j in i:
         print(j)
     print(i)

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元组

元组其实跟列表差不多，也是存一组数，只不是它一旦创建，便不能再修改，所以又叫只读列表

语法：

>>> name = ("Martin", "JMA", "Ly")
>>> name
(‘Martin‘, ‘JMA‘, ‘Ly‘)

它只有2个方法，一个是count,一个是index

2. 字符串操作

特性：不可修改

 

 

3. 字典操作

字典一种key - value 的数据类型，使用就像我们上学用的字典，通过笔划、字母来查对应页的详细内容。

语法：

info = {
    "stud001": "xiaoming",
    "stud002": "xiaohong",
    "stud003": "xiaodong",
    "stud004": "xiaomei"
}

字典的特性：

• dict是无序的
• key必须是唯一的

增加

info["stud005"] = "xiao"
print(info.setdefault("stud004","martin"))  #key存在时打印对应value
print(info.setdefault("stud005","martin"))  #key不存在时增加

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修改

info["stud001"] = "xiao"
info["stud001"] += ",xiao"
{‘stud001‘: ‘xiaoming,xiao‘, ‘stud002‘: ‘xiaohong‘, ‘stud003‘: ‘xiaodong‘, ‘stud004‘: ‘xiaomei‘}

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删除

info.pop("stud001")    #指定删除
info.popitem()    #随机删除
del info["stud002"]   #python的删除方法

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查找

"stud003" in info    #标准用法，判断key是否在字典里，存在未Ture，不存在为False
True
print(info.get("stud001"))    #这个不会，不存在会返回none
print(info["stud001"])    #该方法当key不存在时会报错

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其他操作

print(info.keys())       #获取字典的key列表
print(info.values())    #获取字典的value列表
print(info.items())    #将字典转换成列表
dict_items([(‘stud001‘, ‘xiaoming‘), (‘stud002‘, ‘xiaohong‘), (‘stud003‘, ‘xiaodong‘), (‘stud004‘, ‘xiaomei‘)])

字典循环

方法1：
for key in info:
    print(key,info[key])

方法二：
for k,v in info.items(): #会先把dict转成list,数据量大时莫用
    print(k,v)

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字典更新合并

>>> info
{‘stud001‘: ‘xiaoming‘, ‘stud002‘: ‘xiaohong‘, ‘stud003‘: ‘xiaodong‘, ‘stud004‘: ‘xiaomei‘}
>>> b
{1: 2, 3: 4}
>>> info.update(b)
>>> info
{‘stud001‘: ‘xiaoming‘, ‘stud002‘: ‘xiaohong‘, ‘stud003‘: ‘xiaodong‘, ‘stud004‘: ‘xiaomei‘, 1: 2, 3: 4}

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多级字典嵌套及操作

menu = {
    "jiangxi": {
        "nanchang": {
            "xinjianxian": ["ncu", "bank"],
            "nanchangxian": ["caijingdaxue", "jishuxueyuan"]
        },
        "jiujiang": {
            "xiushuixian": "修水县地图",
            "jiujiangxian": "九江县地图"
        }
    },
    "guangdong": {
        "shenzhen": {
            "longhuaqu": "龙华区地图",
            "luohuqu": "罗湖区地图"
        }
    }
}
menu["jiangxi"]["nanchang"]["xinjianxian"][0] += " univercity"
print(menu["jiangxi"]["nanchang"]["xinjianxian"][0])
ncu univercity

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程序练习

程序: 三级菜单

要求: 

1. 打印省、市、县三级菜单
2. 可返回上一级
3. 可随时退出程序

exit_flag = False
while not exit_flag:
    for i in menu:
        print(i)
    choice = input("1>>:")
    if choice in menu:
        while not exit_flag:
            for i2 in menu[choice]:
                print("\t", i2)
            choice2 = input("2>>:")
            if choice2 in menu[choice]:
                while not exit_flag:
                    for i3 in menu[choice][choice2]:
                        print("\t\t", i3)
                    choice3 = input("3>>:")
                    if choice3 in menu[choice][choice2]:
                        for i4 in menu[choice][choice2][choice3]:
                            print("\t\t\t",i4)
                        choice4 = input("4按b返回上层>>:")
                        if choice4 == "b":
                            pass
                        elif choice4 == "q":
                            exit_flag = True
                    if choice3 == "b":
                        break
                    elif choice3 == "q":
                        exit_flag = True
            if choice2 == "b":
                break
            elif choice2 == "q":
                exit_flag = True

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