[Tutor] file opening modes

[Alan Gauld]

> i.e. append mode so that i can append information to the file while
i am
> running the program.

Yes thats the right approach.

> and three files are generated
>
> a.txt, b.txt, c.txt
>
>
> Now suppose if i run the program again then i get into problem
because now
> again these three files will be appending the information in the
existing
> files which i created last time i run the program.

OK so you need to add a tst for file existence before opening it.
Then if it already exists (and the datestamp is within T seconds
of the current time) then use append othewise use 'w' which will
overwrite the old version.

Alternatively do some housekeeping first and copy the old file to
a .bak before creating the new one.

Put the test in a function:

def alreadyExists(fname):
    # test here

then your code looks like:

if alreadyExists(fname): mode = 'a'
else: mode = 'w'
f = open(fname,mode)

HTH,

Alan g