[Tutor] problem in opening files

[promis at yorku.ca]

I'm am just new to  Python, and am having trouble  getting started. I 
am trying to open  files of data  that  I want to work on, and keep on 
getting a message that  no such  file   exist.  For example here is a 
copy of  what I've typed and the error message


  >>> fo = open('mort.txt')  THIS IS WHAT I TYPED    AND THE MESSAGE FOLLOWS

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    fo = open('mort.txt')
IOError: [Errno 2] No such file or directory: 'mort.txt'
>>>

  The file  mort.txt certainly seems to me to exist. I can see it on my 
desktop.  It was a small  sample file that I just created to  test this 
out. At first I was just  using 'mort', which is what appears on my 
desktop,  but  it was suggested to  me that I should include the 
extension  .txt, which I have verified is the correct extension, so 
that's not the problem anymore.  I have  in fact tried this with a 
number of files  and I get the same message every time.    I am using   
Python versus  3.2.2. ,  on a MAC  with system    OS  10.6.8 .

Any help  would  be  appreciated

David