Add lines to existing file using Python

Question

I already created a txt file using python with a few lines of text that will be read by a simple program. However, I am having some trouble reopening the file and writing additional lines in the file in a later part of the program. (The lines will be written from user input obtained later on.)

with open('file.txt', 'w') as file:
    file.write('input')

This is assuming that 'file.txt' has been opened before and written in. In opening this a second time however, with the code that I currently have, I have to erase everything that was written before and rewrite the new line. Is there a way to prevent this from happening (and possibly cut down on the excessive code of opening the file again)?

Do not use "file" as variable name because it's shadowing the built-in file type — Fabian
– Fabian, Commented Feb 21, 2013 at 15:05

Jeff L · Accepted Answer · 2012-05-17 17:50:19Z

85

Open the file for 'append' rather than 'write'.

with open('file.txt', 'a') as file:
    file.write('input')

answered May 17, 2012 at 17:50

Jeff L

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1 Comment

Vladimir Panteleev Over a year ago

Note! This will not add a newline. If you need to add a line to a text file (as opposed to a line fragment), end the data with \n, e.g.: file.write('input\n')

Danica · Accepted Answer · 2012-05-17 17:49:06Z

79

If you want to append to the file, open it with 'a'. If you want to seek through the file to find the place where you should insert the line, use 'r+'. (docs)

answered May 17, 2012 at 17:49

Danica

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Comments

Ashwini Chaudhary · Accepted Answer · 2014-09-26 18:13:21Z

22

Use 'a', 'a' means append. Anything written to a file opened with 'a' attribute is written at the end of the file.

with open('file.txt', 'a') as file:
    file.write('input')

edited Sep 26, 2014 at 18:13

answered May 17, 2012 at 17:50

Ashwini Chaudhary

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Asclepius · Accepted Answer · 2023-08-11 01:37:27Z

1

If having a pathlib.Path object (instead of a str object), consider using its open method.

with my_path.open(mode='a') as file:
    file.write(f'{my_line}\n')

edited Aug 11, 2023 at 1:37

answered Jun 28, 2023 at 23:51

Asclepius

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