How can I save to a .txt file without overwriting everything that was already in there?

Question

I'm making what is supposed to be just a very basic OS during my free time. However, I'm trying to make it so that you can have as many users as you want, but every time I make a new user, it deletes the old one. So far I have this:

def typer():
    print("Start typing to get started. Unfortunately, you cannot currently save your files.")
    typerCMD = input("  ")
    CMDLine()


def CMDLine():
    print("Hello, and welcome to your new operating system. Type 'help' to get started.")
    cmd = input("~$: ")
    if cmd == ("help"):
        print("Use the 'leave' command to shut down the system. Use the 'type' command to start a text editor.")
    cmdLvl2 = input("~$: ")
    if cmdLvl2 == ("leave"):
        quit()
    if cmdLvl2 == ("type"):
        typer()

def redirect():
    signIn()

def mUserRedirect():
    makeUser()

def PwordSignIn():
    rPword = input("Password: ")
    with open('passwords.txt', 'r') as f:
        for line in f:
            print(line)
            if rPword == (line):
                CMDLine()
            else:
                print("Incorrect password.")
                signIn()

def signIn():
    rUname = input("Username: ")
    with open('usernames.txt', 'r') as f:
        for line in f:
            print(line)
            if rUname == (line):
                PwordSignIn()
            else:
                print("Username not found.")
                mUserRedirect()

def makeUser():
    nUname = input("New username: ")
    nPword = input("Create a password for the user: ")

    with open('usernames.txt', 'w') as f:
        f.write(nUname)
    with open('passwords.txt', 'w') as f:
        f.write(nPword)
    signIn()

print("Create a new user? (Y/N) ")
nUser = input("")
if nUser == ("N"):
    signIn()
if nUser == ("n"):
    signIn()
if nUser == ("Y"):
    makeUser()
if nUser == ("y"):
    makeUser()

So how can I write to the file without getting rid of everything that was already in there?

`w` - open file for writing, place cursor at start of file (e.g. overwrite). you want `w+` - open file for writing, place cursor at END of file (e.g. append). — Marc B, Feb 18 '16 at 19:50
When opening, use mode 'a' for append rather than 'w' for write. — Dan, Feb 18 '16 at 19:50
You can use `a` mode for append to a file , `w` mode writes from start of file — ᴀʀᴍᴀɴ, Feb 18 '16 at 19:51

score 1 · Accepted Answer · answered Feb 18 '16 at 19:52

It depends on the "mode" you're using when opening your file. From the documentation:

'r' open for reading (default)

'w' open for writing, truncating the file first

'a' open for writing, appending to the end of the file if it exists

So all you have to do now is:

with open('usernames.txt', 'a') as f:
    f.write(nUname)

How can I save to a .txt file without overwriting everything that was already in there?

1 Answers1