Avoid crash in iframe renderers when running outside iPython (#1723)

Author: mpaolini

Diff for: packages/python/plotly/plotly/io/_base_renderers.py

@@ -598,8 +598,8 @@ def to_mimebundle(self, fig_dict):
         return {"text/html": iframe_html}
 
     def build_filename(self):
-        ip = IPython.get_ipython()
-        cell_number = list(ip.history_manager.get_tail(1))[0][1] + 1
+        ip = IPython.get_ipython() if IPython else None
+        cell_number = list(ip.history_manager.get_tail(1))[0][1] + 1 if ip else 0
         filename = "{dirname}/figure_{cell_number}.html".format(
             dirname=self.html_directory, cell_number=cell_number
         )