regline.py

def regline(x, y, ax=None, **kwargs):
    b = ((x - x.mean()) * (y - y.mean())).sum() / np.square(x - x.mean()).sum()
    a = y.mean() - b * x.mean()
    x0, x1 = ax.get_xlim()
    r = np.corrcoef(x, y)[0, 1]
    ax.plot([x0, x1], [a + b * x0, a + b * x1], lw=1)
    ax.text(
        0.1,
        0.9,
        f"$\\rho={r:.2f}$",
        horizontalalignment="left",
        verticalalignment="center",
        transform=ax.transAxes,
        fontsize=6,
    )