[Python] ModuleNotFoundError or ImportError: No module named <something>

The following is my directory structure.

ankur
├── ankur1
│ ├── __init__.py
│ └── util.py
├── ankur2
│ └── main.py
└── __init__.py


In main.py, when importing the util submodule:

import ankur.ankur1.util


I get the following error (Python 2.x error message)

ImportError: No module named ankur.ankur1.util


Or (Python 3.x error message)

ModuleNotFoundError: No module named 'ankur'

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