Calculate determinant of an n × n matrix in Python

det.py

# Get the submatrix of A
# Removing the ii-th row and jj-th column
def sub(A, ii, jj):
    matrix = []

    for i in range(len(A)):
        if i == ii:
            continue

        row = A[i].copy()
        row.pop(jj)
        matrix.append(row)

    return matrix

def det(A):
    assert len(A) > 0
    assert len(A) == len(A[0])

    if len(A) == 1:
        return A[0][0]

    value = 0
    sign = 1

    for j in range(len(A[0])):
        value += det(sub(A, 0, j)) * A[0][j] * sign
        # Flip the sign for the next column
        sign = -sign

    return value

# 3x3 Matrix
A = [
    [5, 3, 2],
    [6, 1, 8],
    [9, 6, 7]
]

print(det(A)) # => -61