I have this small script that sorts the content of a text file

# The built-in function `open` opens a file and returns a file object.

# Read mode opens a file for reading only.
try:
    f = open("tracks.txt", "r")


    try:
        # Read the entire contents of a file at once.
       # string = f.read() 
        # OR read one line at a time.
        #line = f.readline()
        # OR read all the lines into a list.
        lines = f.readlines()
        lines.sort()
        f = open('tracks.txt', 'w')
        f.writelines(lines) # Write a sequence of strings to a file
    finally:
        f.close()
except IOError:
    pass

the only problem is that the text is displayed at the bottom of the text file everytime it's sortened...

I assume it also sorts the blank lines...anybody knows why? thanks in advance