force plt clear at start

app.py

@@ -283,10 +283,8 @@ def plot_scatter_hist(x_gene, y_gene, mode='raw'):
 def plt_to_img():
   fig = plt.gcf()
   fig.canvas.draw()
-  image = PIL.Image.frombytes(
+  return PIL.Image.frombytes(
       'RGB', fig.canvas.get_width_height(), fig.canvas.tostring_rgb())
-  plt.close('all')
-  return image
 
 def random_gene():
   return np.random.default_rng().choice(gene_table.columns.values)
@@ -307,6 +305,7 @@ def plot_two_genes(x_gene, y_gene, is_normed):
   return plt_to_img(), f"{x_gene} vs. {y_gene}"
 
 def picker(only_one_gene, x_gene, y_gene, is_normed):
+  plt.close('all')
   if only_one_gene:
     return plot_one_gene(x_gene)
   return plot_two_genes(x_gene, y_gene, is_normed)