newbie question; output from simple print statement

[epost2 at gmail.com]

Can someone explain to me the output of this simple script? I wonder
why ['test1.txt'] is printed before "files in c:\", and also why None
shows up?

________________
in file test.py:

def main():

    print "files in c:\ :%s"  % ListFiles("c:\")

def ListFiles(path):
    for root,dirs,files in os.walk(path):
       print files

if __name__ == "__main__":
    main():

________________
output:

C:\> python test.py
['test1.txt']
files in c:\ :None