python plot creates gray box when using repeating plot

Question

I met some ridiculous thing, don't know what to do with

In my app, I need to process some independent chunks of data and for each chunk create a scatterplot and save to one file and also heatmap and save to another file

So, when I plot the first chunk of data - all is okay.

When I go to 2nd there is some problem, instead of the clean background, it creates a background with gray boxes for a scatterplot graph! That's much confusing for my visualization data.

Below is a simplified example

def test_visual():
    for k in range(0, 3):
        fig = plt.figure()
        ax = fig.add_subplot(111)  # The big subplot
        ax.set_aspect('equal', adjustable='box')

        plt.sca(ax)

        pairs_all = pd.DataFrame({'x': pd.Series(np.zeros(500), dtype=int), 'y': pd.Series(np.zeros(500), dtype=int)})
        sns.scatterplot(data=pairs_all, x="x", y="y", ax=ax, s=0.15)
        # plt.legend([], [], frameon=False)

        ax.legend(loc='upper left', markerscale=0.2, bbox_to_anchor=(1.04, 1), fontsize=2)
        ax.set_xlim(0, 100)
        ax.set_ylim(0, 100)

        # ax.set_xticklabels(ax.get_xticklabels(), fontsize = 4)
        # ax.set_yticklabels(ax.get_yticklabels(), fontsize = 4)

        plt.xticks(np.arange(0, 100 + 1, 5), fontsize=2 )
        plt.yticks(np.arange(0, 100 + 1, 5), fontsize=2 )

        ax.set_xlabel("")
        ax.set_ylabel("")

        fig.tight_layout()

        output_png = '{}_{}.png'.format('file1', k)
        plt.savefig(output_png, dpi=2400, bbox_inches='tight')
        fig.clear()
        plt.close(fig)

        fig = plt.figure()
        ax_w = fig.add_subplot(111)  # The big subplot
        # ax_w.set_aspect('equal', adjustable='box')

        plt.sca(ax_w)

        sns.set(font_scale=0.5)
        sns.heatmap(np.zeros((100, 100)), cbar_kws={'label': 'Energy'}, ax=ax_w, cmap='plasma')

        ax_w.set_xlim(0, 100)
        plt.xticks(fontsize=3)
        plt.yticks(fontsize=3)

        # ax_w.set_title(description, fontweight='bold', fontsize=4)

        fig.tight_layout()

        output_png = '{}_{}.png'.format('file2', k)
        plt.savefig(output_png, dpi=2400, bbox_inches='tight')
        fig.clear()
        plt.close(fig)

That's how it looks for the first run (file file1_0.png)

That's how it looks for the second run (file file1_1.png)

Important notice, that if do not plot heatmap the problem is gone.

So, is this is a bug from the visualization library or I need to adjust my code somehow?

Answer 1

When you execute sns.set(font_scale=0.5) seaborn changes certain matplotlib rc parameters that control the appearance of matplotlib plots. In particular, by default it changes the background color and displays a grid on all subsequently created plots. You can avoid it by removing this line and using a context a manager to set rc parameters only temporarily:

with sns.plotting_context(rc={"font.size": 5.0}):
    sns.heatmap(np.zeros((100, 100)),
                cbar_kws={'label': 'Energy'},
                ax=ax_w,

Alternatively, after plotting the heatmap you can call matplotlib.rc_file_defaults() to restore the original matplotlib rc parameters.