How to write in Python from a text file

Question

I'm trying to open a text file and write to the file but when doing so it's not working at all.

Here's what I have:

changeaddress = [changeaddr1, changeaddr2]
address = [address_1, address_2]
new_var = []
cur_addr = 0
with open('address.txt','r+') as file:
    for line in file:
        if address[cur_addr] in line:
            line.replace(address[cur_addr], changeaddress[cur_addr])
            cur_addr += 1
        new_var.append(line)

with open('address.txt','w') as file:
    file.writelines(new_var)

what I'm doing wrong? it's not working. thanks!

Define it's not working. How does it not work? Why does it not work - what doesn't work as intended? Are you receiving any errors? — Andrew Li
– Andrew Li, Commented Nov 14, 2016 at 5:51
What do you mean by it's not working? What's the actual problem you are facing? — Ahasanul Haque
– Ahasanul Haque, Commented Nov 14, 2016 at 5:51
Have you made sure your script is executable and your file has accessible permissions. — Adam Hopkins
– Adam Hopkins, Commented Nov 14, 2016 at 5:58
@AndrewLi it's just don't work, no errors, it's just don't replace as I expected — Alvaro E
– Alvaro E, Commented Nov 14, 2016 at 13:30

OneCricketeer · Accepted Answer · 2016-11-14 13:49:22Z

1

Strings are immutable. line.replace returns a new string, not literally replaces it.

new_line = line.replace
... 
new_var.append(new_line)

Note: storing the whole list in memory will be bad for large files. You can open two files in one with command to read from one file, and write to another

edited Nov 14, 2016 at 13:49

answered Nov 14, 2016 at 5:56

OneCricketeer

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4 Comments

Alvaro E Over a year ago

I tried but this isn't working, it's not returning any error when I run my script it's just not replacing

OneCricketeer Over a year ago

Probably because you still are writing line, not new line... This is an easy process to debug if you'd just print the values. Get it working before you change your output source

Alvaro E Over a year ago

Thank you, when doing so it deletes the line first line of my .txt leaving just the replaced item. Do you know why is it happening?

OneCricketeer Over a year ago

I'm not sure what you are seeing, but, 1) 'r+' can be removed from the first file. 2) Your code is hard to debug because you completely overwrite the initial file. Try writing to a different one

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