Write to an Existing File
To write to an existing file, you must add a parameter to the open() function:
"a" – Append – will append to the end of the file
"w" – Write – will overwrite any existing content
Example
Open the file “demofile2.txt” and append content to the file:
f = open("demofile2.txt", "a")
f.write("Now the file has more content!")
f.close()
#open and read the file after the appending:
f = open("demofile2.txt", "r")
print(f.read())