Take the determinant of a square matrix in Python

determinant.py

def determinant(matrix):
    if len(matrix) == 1:
        return matrix[0][0]
    if len(matrix) == 2:
        return matrix[0][0] * matrix[1][1] - matrix[0][1] * matrix[1][0]
    sign = 1
    det = 0
    for i in range(len(matrix)):
        det += matrix[0][i] * determinant(minor(matrix, 0, i)) * sign
        sign *= -1
    return det

def minor(matrix, row, col):
    new = [matrix[r][:] for r in range(len(matrix)) if r != row]
    for i in range(len(new)):
        new[i].pop(col)
    return new