So maybe completely deleting and overwriting existing files is something that bothers you. Isn’t there a way to just add a line to a file without completely deleting it? Of course there is! Instead of opening the file using the argument 'w' for write-mode, we open it with 'a' for append-mode. If we have a generated file with the following contents:
generated_file.txt
Then we can add another line to that file with the following code:
script.py
In the code above we open a file object in the temporary variable gen_file. This variable points to the file generated_file.txt and, since it’s open in append-mode, adds the string \n... and it still is to the file. The newline character \n moves to the next line before adding the rest of the string. If you were to open the file after running the script it would look like this:
generated_file.txt
Notice that opening the file in append-mode, with 'a' as an argument to open(), means that using the file object’s .write() method appends whatever is passed to the end of the file. If we were to run script.py again, this would be what generated_file.txt looks like:
generated_file.txt
Notice that we’ve appended "\n... and it still is" to the file a second time! This is because in script.py we opened generated_file.txt in append-mode.
Instructions
We’ve got a file, cool_dogs.txt, filled with all the cool dogs we know. Somehow while compiling this list we forgot about one very cool dog. Let’s fix that problem by adding him to our cool_dogs.txt.
Open up our file cool_dogs.txt in append-mode and assign it to the file object cool_dogs_file.
Inside your with block, add “Air Buddy\n” to cool_dogs.txt. Air Buddy is a Golden Retriever that plays basketball, which more than qualifies him for this list. The \n character moves to the next line after appending the string.