When a module is run under pdb in Python 3, __package__ is set to the empty string instead of None.  The attached minimum working example depicts this behavior.  The results are summarized in the following table.

=============== ====== ======
    Command      Py 2   Py 3
=============== ====== ======
 python          None   None
 python -m        ''     ''
 python -m pdb   None    ''
 pdb             None    ''
=============== ====== ======

The behavior I expected was for the Python executable to treat the input file as a script and not a module.  My rationale is that pdb is loaded as the executing module that accepts a script as its argument.  Per the help, only one -m option is allowed when launching python.