exarkun@charm:~$ ls  .pythonstartup.py
.pythonstartup.py
exarkun@charm:~$ python
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) 
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> __file__
'/home/exarkun/.pythonstartup.py'
>>> 
exarkun@charm:~$ mv .pythonstartup.py .not-pythonstartup.py
exarkun@charm:~$ python
Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) 
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> __file__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name '__file__' is not defined
>>>