python 入门第二课2 file的文件操作

务必注意读/写方式和指针位置

1、文件操作总结
模式'r'或者‘r+’或者‘rb+’指针初始位置在文件开头
模式'w'或者‘w+’或者‘wb+’指针初始位置在文件末尾
模式'a'或者‘a+’或者‘ab+’指针初始位置在文件末尾

模式'w'或者‘w+’或者‘wb+’,新创建文件，会覆盖原文件，慎用
file.truncate(20)，文件从0开始只保留20个字符，其余被清除，慎用
file.readlines()，比较占用资源，对于大文件，尽量不用
file.flush()，强制刷新新写入内容至磁盘

2、文件练习：

__author__ = 'admin'
f = open('file1','r+',encoding='utf-8')

print(f.write('Yello++++'))

'''
import sys,time

for i in range(10):
    sys.stdout.write('#')
    sys.stdout.flush()
    time.sleep(0.2)
f = open('file1','ab+')
f.seek(0)
print(f.readline())
print(f.readline())
print('\n=====\n')
f.write('hello binary'.encode())

print(f.readline())
print(f.tell())
print(f.readline())
print(f.tell())
f.seek(60)
print(f.tell())
print(f.readline())
print()
#print(f.write('\nhello ---====----'))


count = 0
for line in f :
    if count ==9 :
        print(f.write('this is an insert message'))
        count +=1
        continue
    print(f.readline())
    count +=1
'''

3、购物车练习：
readme:商品列表写在文件goods_list中,以只读方式打开，读取第一行，使用eval()函数转变为列表；先以只读方式打开username_info文件，eval（）读取字典方式记录的{‘username’:[[选购清单]，余额]}信息,关闭文件；提示输入用户名，判断用户名是否在username_info中，如果在，直接读取shopping_l 和salary；如果不在，则提示输入salary，然后选购，然后字典添加{‘username’:[[选购清单]，余额]}，最后写入信息，覆盖原先的'username_info'文件

__author__ = 'Administrator'
username = input('Please input your username:')
#f_n = open('usernamelist','r+',encoding='utf-8')
f_n_info = open('username_info','r',encoding='utf-8')
salary = 0
goods_f = open('goods_list','r',encoding='utf-8')
goods_l = eval(goods_f.readline())
goods_f.close()
shopping_l = []
for index, item in enumerate(goods_l,0):
    print(index,item)

def print_shopping():
    print('----shopping list----')
    for i in shopping_l :
        print(i)
    print('Your current balance is :',salary)
    f_dict[username] =[shopping_l,salary]
    f_new_info = open('username_info','w+',encoding='utf-8')
    f_new_info.write(str(f_dict))
    f_new_info.close()
    exit()


f_dict = eval(f_n_info.readline())
f_n_info.close()
if username in f_dict.keys() :

    shopping_l =f_dict[username][0]
    salary = f_dict[username][1]
    print(shopping_l,'\n',salary)
else:
    salary = input('Please input your salary:')
    if salary.isdigit() :
        salary = int(salary)
        while True :
            choice = input('Please input the goods number (%s-%s):'%(0,len(goods_l)))
            if choice.isdigit() :
                choice = int(choice)
                if choice < len(goods_l) and choice >= -1 :
                    p_item = goods_l[choice]
                    if p_item[1] <= salary :
                        shopping_l.append(p_item[0])
                        salary -= p_item[1]
                        print('Add %s into your shopping cart,your current balance is:\033[31;1m %s\033[0m '%(p_item[0],salary))
                    else :
                        print('You have no enough money.')
                        print_shopping()

                else :
                    print('Invalid number,please input again.')

            elif choice == 'q'or choice == 'Q' :
                print_shopping()

    #            print('----shopping list----')
    #            for i in shopping_l :
    #                print(i)
    #            print('Your current balance is :',salary)
    #            exit()


            else:
                print('Invalid input,please input a number.')

    else:
        print('Invalid input')


#for i in goods_l :
#    print(goods_l.index(i),i)