读取、写入文件 、存储数据

1、读取文件

一、读取整个文件

file_name = 'cat.txt'

with open(file_name) as file_object:

　 contents = file_object.read()

　print(contents)　

二、逐行读取，可以使用for循环

file_name = 'cat.txt'

with open(file_name) as file_object:

　　for line in file_object:

　　　　print(line.rstrip())

三、建立一个包含文件各行内容的列表

file_name = 'cat.txt'

with open(file_name) as file_object:

　　lines = file_object.readlines()

for line in lines:

　　print(line.rstrip())

四、使用文件的内容

file_name ='pi.txt'

with open(file_name) as file_object:

　　lines = file_object.readlines()

pi_string = ' '

for line in lines:

　　pi_string += line

print(pi_string)

2、写入文件

一、‘w’写入

with open(filename,'w') as file_object:

　　file_object.write(I want to hide")

注：写入多行时后面须要加换行符。

二、‘a'附加　　

with open(filename,'a') as file_object:

　　file_object.write('I want to sleep')

3、异常

try-except-else

else在try代码块中执行成功时运行else代码块。

4、存储数据

一、json.dump() 接受两个实参，要存储的数据，以及要存储数据的文件类型

   json.load()接受一个实参，文件类型

二、如何用json.dump()来存储列表

import json

numbers = [1,2,3,4,5,6]

filename = number.josn

with open(filename,'w') as file_object:

　　josn.dump(numbers,file_object)

三、保存和读取用户生成的数据

import json
file_name = 'number.json'
try:
    with open(file_name) as file_object:
        fav_number = json.load(file_object)

except:
    number = input("请输入你喜欢的数字：")
    with open(file_name,'w') as file_object:
        fav_number = json.dump(number,file_object)
else:
    print("您最喜欢的数字是：%s" % fav_number)

四、重构

import json
file_name = 'username.json'
def got_name():
    """获取用户名称"""
    try:
        with open(file_name) as file_object:
            user_name = json.load(file_object)
    except:
        return None
    else:
        return user_name

def new_name():
    """提醒用户输入名字"""
    user_name = input("请输入您的名字：")
    with open(file_name,'w') as file_object:
        put_name = json.dump(user_name,file_object)
        return user_name


def greet():
    """向用户发出问候"""
    username = got_name()
    if username:
        ask = input("用户名是%s吗?"%username)
        if ask == 'y':
            print("欢迎回来%s"%username)
        else:
            user_name =new_name()
            print("下次我会记得你哦！%s"%user_name)
    else:
        user_name = new_name()
        print("下次我会记得你哦！%s" % user_name)
greet()