如何对2D列表中的列求和？

def column_sums(matrix):
    row_count = len(matrix)
    col_count = len(matrix[0])
    col_sums = [0] * col_count

    for row in matrix:
        for col_idx, val in enumerate(row):
            col_sums[col_idx] += val

    return col_sums

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

col_sums = column_sums(matrix)
print(col_sums)  # 输出：[12, 15, 18]