~ after script filename?

[presentt]

Hello all,

I just wrote a really simple script and named it helloworld.py.  Inside
was only:

#!/usr/bin/env
print "Hello, world"

I used chmod to set the permissions, and ran it to see what happened (I
just started learning Python, if you couldn't guess)

Then, I typed ls in the directory to see what was there, and I noticed
a new file, namely helloworld.py~ .  What is that file (its contents
are identicle to helloworld.py)?  Why the ~?

Thanks a lot.  I'm using Ubuntu Linux 5.04 (Hoary), and wrote the
script with gedit.

~~Ted Present