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>

matrix/sherman_morrison.py

@@ -11,7 +11,7 @@ class Matrix:
 
         Example:
         >>> a = Matrix(2, 3, 1)
-        >>> a 
+        >>> a
         Matrix consist of 2 rows and 3 columns
         [1, 1, 1]
         [1, 1, 1]
@@ -186,10 +186,10 @@ class Matrix:
 
         Example:
         >>> a = Matrix(2, 3)
-        >>> for r in range(2):       
+        >>> for r in range(2):
         ...     for c in range(3):
         ...             a[r,c] = r*c
-        ... 
+        ...
         >>> a.transpose()
         Matrix consist of 3 rows and 2 columns
         [0, 0]
@@ -209,14 +209,14 @@ class Matrix:
         Apply Sherman-Morrison formula in O(n^2).
         To learn this formula, please look this: https://en.wikipedia.org/wiki/Sherman%E2%80%93Morrison_formula
         This method returns (A + uv^T)^(-1) where A^(-1) is self. Returns None if it's impossible to calculate.
-        Warning: This method doesn't check if self is invertible. 
+        Warning: This method doesn't check if self is invertible.
             Make sure self is invertible before execute this method.
 
         Example:
         >>> ainv = Matrix(3, 3, 0)
         >>> for i in range(3): ainv[i,i] = 1
-        ... 
-        >>> u = Matrix(3, 1, 0) 
+        ...
+        >>> u = Matrix(3, 1, 0)
         >>> u[0,0], u[1,0], u[2,0] = 1, 2, -3
         >>> v = Matrix(3, 1, 0)
         >>> v[0,0], v[1,0], v[2,0] = 4, -2, 5