human
I wrote the below code

    (means, stdevs) = scale(data_matrix)
    def rescaled(i, j):
        if (stdevs[j] > 0):
            return ((data_matrix[i][j] - means[j]) / stdevs[j])
        else:
            return data_matrix[i][j]
    (num_rows, num_cols) = shape(data_matrix)
    return make_matrix(num_rows, num_cols, rescaled)

What's a good function header?
 ... Here's a good function header?
assistant
#Here's a good function header.

def rescale(data_matrix):