How can I fix the Plotly Heatmap block size?

Here is my HeatMap plot function:

def plot_heatmap(alphas, k_list, title_prefix="", years=["Y2013", "Y2014"]):
    data = [
        Heatmap(
            name = "",
            z = alphas,
            x = years,
            y = k_list,
            hoverongaps = False,
            zauto = False,
            zmin = zmin,
            zmax = zmax,
            colorscale = color_custom,
            colorbar = dict(
                title = "Alpha Value",
                thicknessmode = "pixels",
                thickness = 50,
                yanchor = "top",
                y = 1,
                len = 480,
                lenmode = "pixels",
                ticks = "outside",
                dtick = zmax / 10
                )
        )
    ]
    fig = Figure(
        data = data,
        layout = Layout(
            width = 640,
            height = round(60 * len(k_list)) if round(60 * len(k_list)) > 640 else 640,
            # autosize = True,
            title = title_prefix + " | HeatMap : alphas",
        )
    )
    fig.data[0]['hoverinfo'] = 'all'
    fig['layout']['yaxis']['scaleanchor'] = 'x'
    iplot(fig)

Right now, my workaround is height = round(60 * len(k_list)) if round(60 * len(k_list)) > 640 else 640, in the *Layout object.

The result is like this:

I don't want to see the grey parts on the plot; how can I do that?

I think that for some reason Plotly takes your years input to be numerical. You can make this variable explicitly categorical by adding

fig['layout']['xaxis']['type'] = 'category'