python 2.5 - f=open('a_file.txt','w') gives [Errno 2]

[dirkheld]

Hi,

I upgraded my system from tiger to leopard. With leopard came a new
version of python 2.5

Now I trying to run some python code that previously worked on tiger
(which included an older version of python).

This is the error I'm receiving :

Traceback (most recent call last):
  File "test.py", line 18, in print_total
    f=open('a_file.txt','w')
IOError: [Errno 2] No such file or directory: 'a_file.txt'


Is this a bug in python? This code worked on my old system