* adding static type checking to basic_binary_tree.py
* Add static type checking to functions with None return type
* Applying code review comments
* Added missing import statement
* fix spaciing
* "cleaned up depth_of_tree"
* Add doctests and then streamline display() and is_full_binary_tree()
Co-authored-by: Christian Clauss <cclauss@me.com>
* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>