This is a demonstration of an ImportError with sys.path being correct.
The cause is os.chdir() followed by a package-intern import, see
__main__.py. Importing the problematic module in __init__.py fixes the
problem.
For me this ImportError was hard to debug and the available information rather sparse. The original issue is described at StackOverflow.
Usage
Clone the repository. Get the ImportError with:
python -m importerror
whereas this works (does not raise an ImportError):
python importerror/__main__.py