Fixed ValueError exception which can occur when opening an old format persistent history file with a new version of cmd2

Author: tleonhardt

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.19 (TBD, 2019)
+* Bug Fixes
+    * Fixed `ValueError` exception which could occur when an old format persistent history file is loaded with new `cmd2`
+
 ## 0.9.18 (October 1, 2019)
 * Bug Fixes
     * Fixed bug introduced in 0.9.17 where help functions for hidden and disabled commands were not being filtered

cmd2/cmd2.py

@@ -3592,7 +3592,8 @@ def _initialize_history(self, hist_file):
         try:
             with open(hist_file, 'rb') as fobj:
                 history = pickle.load(fobj)
-        except (AttributeError, EOFError, FileNotFoundError, ImportError, IndexError, KeyError, pickle.UnpicklingError):
+        except (AttributeError, EOFError, FileNotFoundError, ImportError, IndexError, KeyError, ValueError,
+                pickle.UnpicklingError):
             # If any non-operating system error occurs when attempting to unpickle, just use an empty history
             pass
         except OSError as ex: