Merge pull request #12247 from meeseeksmachine/auto-backport-of-pr-12219-on-7.x

Backport PR  #12219 on branch 7.x (Catch ValueError)

IPython/core/debugger.py

@@ -622,7 +622,11 b' class Pdb(OldPdb):'
         Take a number as argument as an (optional) number of context line to
         print"""
         if arg:
-            context = int(arg)
+            try:
+                context = int(arg)
+            except ValueError as err:
+                self.error(err)
+                return
             self.print_stack_trace(context)
         else:
             self.print_stack_trace()