Tighten up psf/black and flake8 (#2024)

* 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>

linear_algebra/src/test_linear_algebra.py

@@ -19,7 +19,7 @@ class Test(unittest.TestCase):
         x = Vector([1, 2, 3])
         self.assertEqual(x.component(0), 1)
         self.assertEqual(x.component(2), 3)
-        y = Vector()
+        _ = Vector()
 
     def test_str(self):
         """