如何用另一条线替换一条线？

Question

I am trying to make a contact book application with command-line arguments. This is the code written so far to update the new contact details of a particular contact. args.name has the name of the contact. And args.number has the new number which needs to be updated.

How can I update the entire line? When I run this, it replaces the entire file, contacts.txt , with an empty string. This functionality will also help in the delete function.

thefile = open("contacts.txt","w+")
lines = thefile.readlines()
for line in lines:
     if name in line:
           line.replace(line,"Name: "+ args.name + " Number: "+args.number+ "\n")

Answer 1

You could firstly read the data from the file, create an empty string, append each line to the newly created string conditionally, and write(replace) the newly obtained string onto the existing file.

f1 = open('contacts.txt','r')

data = f1.readlines()
f1.close()
new_data = ""

for line in data:
   if name in line:
     update = line.replace(line,"Name: "+ args.name + " Number: "+args.number+ "\n")
     new_data += update
   else:
     new_data += line

f2 = open('contacts.txt','w')
f2.write(new_data)
f2.close()

Answer 2

When you open a file with "w+" python erase the file: First you whoud write two function: One that writes data and the other read data

def reader():
    f = open("MYFILE.txt", "r")
    lines = f.readlines()
    f.close()
    return lines

def writer(data):
    f = open("MYFILE.txt", "w")
    for i in data:
        f.write(i)
    f.close()

Then you can actualise lines how you want:

lines = reader()

for i in range(len(lines)):
    if lines[i] == "Something\n":
        lines[i] = "New_Value\n"
writer(lines)