with open('a.txt',mode='rt',encoding='utf-8') as f:
data=f.read()
 print(data)

with open('a.txt',mode='wt',encoding='utf-8') as f:
 f.write('hello world')

with open ('a.txt',mode='rb') as af, open('b.txt',mode='wb') as bf:
 data=af.read
 f.write(data) 

with open('a.txt',mode='rt',encoding='utf-8') as f:
 data=f.read()
 data_new=data.replace('yang', 'yv')
with open('b.txt',mode='wt',encoding='utf-8')as p:
 p.write(data_new)

import os
with open('b.txt',mode='rt',encoding='utf-8') as f, open('.b.txt.swap',mode='wt',encoding='utf-8') as p:
 for line in f:
 p.write(line.replace('yv','yang')) 
 # 调用replace方法,将源文件中的'yv',换成'yang'
os.remove('b.txt')
os.rename('.b.txt.swap','b.txt')

# 0
with open('a.txt',mode='rt',encoding='utf-8')as f:
 f.seek(3,0)
 print(f.tell()) # 指针当前位置
 print(f.read()) # 从指针后读出所有内容

# 1 参照指针当前位置
 with open('a.txt',mode='rb')as f:
 f.read(2)
 f.seek(4,1)
 print(f.tell())
 print(f.read().decode('utf-8'))

# 2 参照文件末尾
 with open('a.txt',mode='rb')as f:
 f.seek(-5,2)
 print(f.tell())
 print(f.read().decode('utf-8'))

# 另一个文件进行写操作，写的代码如下：

with open('a.txt',mode='at',encoding='utf-8')as f:
 f.write('hello world\n')


# 每在文件中写入新的内容，都打印出来，以下代码执行打印操作：
import time
with open('a.txt',mode='rb')as f:
 f.seek(0,2)
 while True:
 line=f.readline() # readline 可以读取没有内容的部分
 # print(line.decode('utf-8'))
 if len(line)==0:
 time.sleep(0.1)
 else:
 print(line.decode('utf-8'))