Merge pull request #32 from Mathics3/fix_ovelaid_graphs

closing pyplot before draw

Author: rocky

pymathics/graph/format.py

@@ -35,7 +35,7 @@ def format_graph(G, **options) -> str:
 
     global node_size
     global cached_pair
-
+    pyplot.close()
     pyplot.switch_backend("AGG")
     cached_pair = None