In python there is no difference between modules and scripts; You can execute both scripts and modules. The file must be on the pythonpath AFAIK because python must be able to find the file in question. If python is executed from a directory, then the directory is automatically added to the pythonpath.
Refer to What is the best way to call a Python script from another Python script? for more information about modules vs scripts
There is also a builtin function execfile(filename) that will do what you want