python学习之路2

1. 列表、元组操作

　　列表是我们最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

1 cars = ["Camry","Accord","Teana"]

　　访问列表中的元素，方式如下

#列表第一个
>>>cars[0]
Camry
#列表最后一个
>>>cars[-1]
Teana
#列表第二个
>>>cars[1]
Accord

　　切片取元素

>>> cars = ["Camry","Accord","Teana","Q50","ES","320i","S60L"]
#取第二到第三个元素
>>> cars[1:3]
['Accord', 'Teana']
#取第一到最后一个元素但不包含最后一个元素
>>> cars[0:-1]
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i']
#取第一到最后一个元素
>>> cars[0:]
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i', 'S60L']
#第一到最后一个元素，每隔三个取一个
>>> cars[0::3]
['Camry', 'Q50', 'S60L']

　　添加

>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i', 'S60L']
>>> cars.append("A3")
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i', 'S60L', 'A3']

　　插入

>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i', 'S60L', 'A3']
>>> cars.insert(3,"Corolla")
>>> cars
['Camry', 'Accord', 'Teana', 'Corolla', 'Q50', 'ES', '320i', 'S60L', 'A3']

　　修改

>>> cars
['Camry', 'Accord', 'Teana', 'Corolla', 'Q50', 'ES', '320i', 'S60L', 'A3']
>>> cars[-1] = "A4"
>>> cars
['Camry', 'Accord', 'Teana', 'Corolla', 'Q50', 'ES', '320i', 'S60L', 'A4']

　　删除

>>> cars
['Camry', 'Accord', 'Teana', 'Corolla', 'Q50', 'ES', '320i', 'S60L', 'A4']
#删除第四个元素
>>> del cars[3]
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', '320i', 'S60L', 'A4']
#指定名称删除元素320i
>>> cars.remove("320i")
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L', 'A4']
#弹出最后一个元素
>>> cars.pop()
'A4'
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L']

　　合并

>>> brands = ["Toyota","Nissan","Honda"]
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L']
#将cars与brands合并
>>> cars.extend(brands)
>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L', 'Toyota', 'Nissan', 'Honda']
>>> brands
['Toyota', 'Nissan', 'Honda']

　　拷贝

>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L', 'Toyota', 'Nissan', 'Honda']
>>> cars_copy = cars.copy()
>>> cars_copy
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L', 'Toyota', 'Nissan', 'Honda']

　　统计

>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L', 'Toyota', 'Nissan', 'Honda']
>>> cars.count("ES")
1

　　排序&逆序

>>> cars
['Camry', 'Accord', 'Teana', 'Q50', 'ES', 'S60L']
>>> cars.sort()
>>> cars
['Accord', 'Camry', 'ES', 'Q50', 'S60L', 'Teana']
>>> cars.reverse()
>>> cars
['Teana', 'S60L', 'Q50', 'ES', 'Camry', 'Accord']

　　获取下标

>>> cars
['Teana', 'S60L', 'Q50', 'ES', 'Camry', 'Accord']
>>> cars.index("ES")
3

元祖

元组与列表类似，也是存一组数，只是一旦被创建，便不能再修改，所以又叫只读列表

>>> cars = ['Teana', 'S60L', 'Q50', 'ES', 'Camry', 'Accord']

它只有2个方法，一个是count,一个是index。

程序练习 

程序：购物车程序

需求:

1. 启动程序后，让用户输入工资，然后打印商品列表
2. 允许用户根据商品编号购买商品
3. 用户选择商品后，检测余额是否够，够就直接扣款，不够就提醒 
4. 可随时退出，退出时，打印已购买商品和余额

product_list = [
    ("Iphone",5000),
    ("Mac Pro",13000),
    ("Iwatch",3000),
    ("Bike",1000),
    ("Book",80),
    ("Coffee",30),
]
shopping_list = []
salary = input("input you salary:")
if salary.isdigit():
    salary = int(salary)
    while True:
        for item in product_list:
            print(product_list.index(item),item)
        user_choice = input("选择要买啥？>>>:")
        if user_choice.isdigit():
            user_choice = int(user_choice)
            if user_choice < len(product_list) and user_choice >=0:
                p_item = product_list[user_choice]
                if p_item[1] <= salary: #买得起
                    shopping_list.append(p_item)
                    salary -= p_item[1]
                    print("added %s into shopping cart,your current balance is [%s]"% (item,salary))
                else:
                    print("你的余额只剩[%s]啦，买不起啦"% (salary))
            else:
                print("product code [%s] is not exist!"% user_choice)
        elif user_choice == "q":
            print("--------shopping list--------")
            for p in shopping_list:
                print(p)
            print("your currnt balance:",salary)
            exit()
        else:
            print("invalid option")
37 else:
38 　　print("invalid option")

二、字符串 

 name.capitalize()  首字母大写
 name.casefold()   大写全部变小写
 name.center(50,"-")  输出 '---------------------xxx----------------------'
 name.count('x') 统计 x出现次数
 name.encode()  将字符串编码成bytes格式
 name.endswith("x")  判断字符串是否以x结尾
 "xx\tx".expandtabs(10) 输出'xx      x'， 将\t转换成多长的空格 
 name.find('A')  查找A,找到返回其索引， 找不到返回-1 
  
 format :
     >>> msg = "my name is {}, and age is {}"
     >>> msg.format("xxx",26)
     'my name is xxx, and age is 26'
     >>> msg = "my name is {1}, and age is {0}"
     >>> msg.format("xxx",26)
     'my name is 26, and age is xxx'
     >>> msg = "my name is {name}, and age is {age}"
     >>> msg.format(age=26,name="xxx")
     'my name is xxx, and age is 26'
 format_map
     >>> msg.format_map({'name':'xxx','age':26})
     'my name is xxx, and age is 26'
 
 
msg.index('x')  返回x所在字符串的索引
 
 
'9'.isdigit() 是否整数
name.isnumeric  
name.isprintable
name.isspace
name.istitle
name.isupper
"|".join(['xxx','jack','rain'])
'xxx|jack|rain'
 
 
maketrans
    >>> intab = "aeiou"  #This is the string having actual characters. 
    >>> outtab = "12345" #This is the string having corresponding mapping character
    >>> trantab = str.maketrans(intab, outtab)
    >>> 
    >>> str = "this is string example....wow!!!"
    >>> str.translate(trantab)
    'th3s 3s str3ng 2x1mpl2....w4w!!!'

msg.swapcase 大小写互换
 
 
>>> msg.zfill(40)
'00000my name is {name}, and age is {age}'
 
 

>>> n4.ljust(40,"-")
'Hello 2orld-----------------------------'
>>> n4.rjust(40,"-")
'-----------------------------Hello 2orld'
 
 
>>> b="ddefdsdff_哦" 
>>> b.isidentifier() #检测一段字符串可否被当作标志符，即是否符合变量命名规则
True