calculate determinant of a (square) matrix

determinant.py

from typing import TypeVar

T = TypeVar("T", int, float)
Matrix = list[list[T]]


def is_square(matrix: Matrix):
    n = len(matrix)
    for row in matrix:
        if len(row) != n:
            return False

    return True


def determinant(matrix: Matrix):
    assert is_square(matrix)
    n = len(matrix)
    if n == 1:
        return matrix[0][0]
    det = 0
    sign = 1
    for i, major in enumerate(matrix[0]):
        sub_matrix: Matrix = []
        for other_row in matrix[1:]:
            other_row = other_row.copy()
            other_row.pop(i)
            sub_matrix.append(other_row)
        det += major * sign * determinant(sub_matrix)
        sign *= -1

    return det


if __name__ == "__main__":
    m1 = [[1, 2], [3, 4]]
    m2 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
    m3 = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]
    print(determinant(m1))
    print(determinant(m2))
    print(determinant(m3))