Convenience method to plot data with trend lines based on polynomial fit.

    Args:
        x: Sequence of x data.
        y: Sequence of y data.
        deg (int): Degree of polynomial. Defaults to 1.
        xlabel (str): Label for x-axis.
        ylabel (str): Label for y-axis.
        \\*\\*kwargs: Keyword args passed to pretty_plot.

    Returns:
        matplotlib.pyplot object.

def pretty_polyfit_plot(x, y, deg=1, xlabel=None, ylabel=None, **kwargs):
    """
    Convenience method to plot data with trend lines based on polynomial fit.

    Args:
        x: Sequence of x data.
        y: Sequence of y data.
        deg (int): Degree of polynomial. Defaults to 1.
        xlabel (str): Label for x-axis.
        ylabel (str): Label for y-axis.
        \\*\\*kwargs: Keyword args passed to pretty_plot.

    Returns:
        matplotlib.pyplot object.
    """
    plt = pretty_plot(**kwargs)
    pp = np.polyfit(x, y, deg)
    xp = np.linspace(min(x), max(x), 200)
    plt.plot(xp, np.polyval(pp, xp), 'k--', x, y, 'o')
    if xlabel:
        plt.xlabel(xlabel)
    if ylabel:
        plt.ylabel(ylabel)
    return plt