Relative import in Python

For some time now (since relative imports were removed), I haven't been able to properly solve this issue:

Suppose the program structure is

app/    __init__.py    foo/        __init__.py        handler.py

How can I load something from the foo package from the handler.py module?

The thing is that the name of the foo package is initially unknown, I load it using importlib.

So far I've found this workaround: I truncate the __name__ variable, which in handler.py equals 'foo.handler', like this

foo_name = __name__.rsplit('.', 1)[0]

and then load