How to do step-by-step debugging for a Python package in PyCharm 5?

Question

I have a Python package in PyCharm, they run in the following format:

python -m mypackage 

However, as the code grows, I need to track data changes, so I need to do this step by step. I tried to debug it as a script, but PyCharm prevented me by mistake:

ValueError: Attempting to relative import in non-packet

I have to store this relative import data, since it is also written as Python packages.

Can anyone teach me how to do this in PyCharm5?

Thank you very much.