Chapter 3 File Operations

File operations are divided into read and write modifications 

Example:

f =open(file='db.txt',mode='r',encoding='utf-8') r read-only r+ read-write w+ write-read w write rb read in binary mode a append the content to the end of the file

data=f.read()

f.close()

 

loop file

f = open(file='db.txt','r',encoding="utf-8")

for line in f :

    print (line)

f.close()

 

write file

f = open(file='db.txt','w',encoding="utf-8")

f.write('aslkfladfasdf')

f.close()

Example of file modification code in hard disk mode

 

 

Simulate login

import them

f = oopen(f_name,'r',encoding='utf-8')

f_new=open(f_new_name,'w',encoding='utf-8')

for line in f:

    if old_str in line:

        new_line = line.replace(old_str,new_str)

    else:

        new_line = line

    f_new.write(new_line)

f.close()

f_new.close()

os.rename(f_new_name,f_name)

while True:

name=input('Please enter the username >>: ')

with open ('lock.txt','r',encoding='utf-8') as read_f:

 f=read_f.read()

if name in f:

    print('Secondary user is locked')

break 

psw=input('Please enter your password>>: ')

with open ('user.txt','r',encoding='utf-8') as read_f:

for line in read_f:

    l=line.strip().split(',')

   if name==l[0] and psw==l[1]:

    print('Login successful'')

    break

    else:

   

       print('Please re-enter')

     count+=1

  if count=3 :

 with open ('lock.txt','w',encoding='utf-8') as write_f:

    write_f.write(name)

    print('User is locked')

    break

 

 

global replacement

import sys
import os 
count=0
if len(sys.argv) != 3:
    print('usage: cp source_file target_file')
    sys.exit()

old_str,new_str=sys.argv[1],sys.argv[2] 
with open(f_new_name,'rb') as f,open(f_new_name,'wb') as f_new:

for line in f:
if old_str in line:
    new_line=line.replace(old_str,new_str)
    count+=1
else:
    new)line=line
f_new.write(new_line)
os.rename(f_new_name,f_name)
print('count')