Pdb fails to launch any scripts that uses the __file__ builtin.
This problem occurs because pdb does not set the global environnement
correctly.

It can be corrected by setting the global variable __file__ before pdb
executes the file.

Lib/pdb.py:
Replace : globals_ = {"__name__" : "__main__"} 
by: globals_ = {"__name__" : "__main__", "__file__": filename}

The problem happens also in python 2.5.