After changing Python installations on Windows, you may find that Python is ignoring the commandline parameters passed to a Python script.
To fix this, open regedit.exe, head over to HKEY_CLASSES_ROOT\Applications\python.exe\shell\open\command and make sure the value field is "C:\PYTHON_PATH\python.exe" "%1" %*. If the %* is missing, then the Python script will not have access to the commandline parameters passed to it.