[Lesson 02] Standardization of the docstrings.
[Lesson 03] Standardization of the docstrings.
[Lesson 04] Standardization of the docstrings.
[Lesson 04] Minor typo in docstrings of sink function.
[Lesson 04] Add blank line in functions.
[Lesson 06] Standardization of the docstrings.
[Lesson 07] Standardization of the docstrings.