How to write to .txt files in Python 3

Question

I have a .txt file in the same folder as this .py file and it has this in it:

cat\\n
dog\\n
rat\\n
cow\\n

How can

Answer 1

Open the file in append mode and write a new line (including a \n line separator):

with open(filename, 'a') as out:
    out.write(var + '\n')

This adds the line at the end of the file after all the other contents.