Handle absent lzma library

cmd2/cmd2.py

@@ -4627,7 +4627,7 @@ def do_ipy(self, _: argparse.Namespace) -> Optional[bool]:  # pragma: no cover
             )
 
             # Start IPython
-            start_ipython(config=config, argv=[], user_ns=local_vars)
+            start_ipython(config=config, argv=[], user_ns=local_vars)  # type: ignore[no-untyped-call]
             self.poutput("Now exiting IPython shell...")
 
             # The IPython application is a singleton and won't be recreated next time
@@ -4814,11 +4814,9 @@ def _initialize_history(self, hist_file: str) -> None:
                           previous sessions will be included. Additionally, all history will be written
                           to this file when the application exits.
         """
-        import json
-        import lzma
-
         self.history = History()
-        # with no persistent history, nothing else in this method is relevant
+
+        # With no persistent history, nothing else in this method is relevant
         if not hist_file:
             self.persistent_history_file = hist_file
             return
@@ -4839,28 +4837,60 @@ def _initialize_history(self, hist_file: str) -> None:
             self.perror(f"Error creating persistent history file directory '{hist_file_dir}': {ex}")
             return
 
-        # Read and process history file
+        # Read history file
         try:
             with open(hist_file, 'rb') as fobj:
                 compressed_bytes = fobj.read()
-            history_json = lzma.decompress(compressed_bytes).decode(encoding='utf-8')
-            self.history = History.from_json(history_json)
         except FileNotFoundError:
-            # Just use an empty history
-            pass
+            compressed_bytes = bytes()
         except OSError as ex:
             self.perror(f"Cannot read persistent history file '{hist_file}': {ex}")
             return
-        except (json.JSONDecodeError, lzma.LZMAError, KeyError, UnicodeDecodeError, ValueError) as ex:
+
+        # Register a function to write history at save
+        import atexit
+
+        self.persistent_history_file = hist_file
+        atexit.register(self._persist_history)
+
+        # Empty or nonexistent history file. Nothing more to do.
+        if not compressed_bytes:
+            return
+
+        # Decompress history data
+        try:
+            import lzma as decompress_lib
+
+            decompress_exceptions: Tuple[type[Exception]] = (decompress_lib.LZMAError,)
+        except ModuleNotFoundError:  # pragma: no cover
+            import bz2 as decompress_lib  # type: ignore[no-redef]
+
+            decompress_exceptions: Tuple[type[Exception]] = (OSError, ValueError)  # type: ignore[no-redef]
+
+        try:
+            history_json = decompress_lib.decompress(compressed_bytes).decode(encoding='utf-8')
+        except decompress_exceptions as ex:
+            self.perror(
+                f"Error decompressing persistent history data '{hist_file}': {ex}\n"
+                f"The history file will be recreated when this application exits."
+            )
+            return
+
+        # Decode history json
+        import json
+
+        try:
+            self.history = History.from_json(history_json)
+        except (json.JSONDecodeError, KeyError, ValueError) as ex:
             self.perror(
-                f"Error processing persistent history file '{hist_file}': {ex}\n"
+                f"Error processing persistent history data '{hist_file}': {ex}\n"
                 f"The history file will be recreated when this application exits."
             )
+            return
 
         self.history.start_session()
-        self.persistent_history_file = hist_file
 
-        # populate readline history
+        # Populate readline history
         if rl_type != RlType.NONE:
             last = None
             for item in self.history:
@@ -4872,25 +4902,21 @@ def _initialize_history(self, hist_file: str) -> None:
                         readline.add_history(line)
                         last = line
 
-        # register a function to write history at save
-        # if the history file is in plain text format from 0.9.12 or lower
-        # this will fail, and the history in the plain text file will be lost
-        import atexit
-
-        atexit.register(self._persist_history)
-
     def _persist_history(self) -> None:
         """Write history out to the persistent history file as compressed JSON"""
-        import lzma
-
         if not self.persistent_history_file:
             return
 
-        self.history.truncate(self._persistent_history_length)
         try:
-            history_json = self.history.to_json()
-            compressed_bytes = lzma.compress(history_json.encode(encoding='utf-8'))
+            import lzma as compress_lib
+        except ModuleNotFoundError:  # pragma: no cover
+            import bz2 as compress_lib  # type: ignore[no-redef]
+
+        self.history.truncate(self._persistent_history_length)
+        history_json = self.history.to_json()
+        compressed_bytes = compress_lib.compress(history_json.encode(encoding='utf-8'))
 
+        try:
             with open(self.persistent_history_file, 'wb') as fobj:
                 fobj.write(compressed_bytes)
         except OSError as ex: