Show exception cause/context when printing an exception.

Author: jonathanslenders

ptpython/printer.py

@@ -254,8 +254,7 @@ def _apply_soft_wrapping(
                     columns_in_buffer += width
                     current_line.append((style, c))
 
-            if len(current_line) > 0:
-                yield current_line
+            yield current_line
 
     def _print_paginated_formatted_text(
         self, lines: Iterable[StyleAndTextTuples]
@@ -323,14 +322,20 @@ def show_pager() -> None:
     def _format_exception_output(
         self, e: BaseException, highlight: bool
     ) -> Generator[OneStyleAndTextTuple, None, None]:
-        # Instead of just calling ``traceback.format_exc``, we take the
-        # traceback and skip the bottom calls of this framework.
-        t, v, tb = sys.exc_info()
-
-        # Required for pdb.post_mortem() to work.
-        sys.last_type, sys.last_value, sys.last_traceback = t, v, tb
-
-        tblist = list(traceback.extract_tb(tb))
+        if e.__cause__:
+            yield from self._format_exception_output(e.__cause__, highlight=highlight)
+            yield (
+                "",
+                "\nThe above exception was the direct cause of the following exception:\n\n",
+            )
+        elif e.__context__:
+            yield from self._format_exception_output(e.__context__, highlight=highlight)
+            yield (
+                "",
+                "\nDuring handling of the above exception, another exception occurred:\n\n",
+            )
+
+        tblist = list(traceback.extract_tb(e.__traceback__))
 
         for line_nr, tb_tuple in enumerate(tblist):
             if tb_tuple[0] == "<stdin>":
@@ -340,7 +345,7 @@ def _format_exception_output(
         tb_list = traceback.format_list(tblist)
         if tb_list:
             tb_list.insert(0, "Traceback (most recent call last):\n")
-        tb_list.extend(traceback.format_exception_only(t, v))
+        tb_list.extend(traceback.format_exception_only(type(e), e))
 
         tb_str = "".join(tb_list)
 

ptpython/repl.py

@@ -378,6 +378,10 @@ def _compile_with_flags(self, code: str, mode: str) -> Any:
         )
 
     def _handle_exception(self, e: BaseException) -> None:
+        # Required for pdb.post_mortem() to work.
+        t, v, tb = sys.exc_info()
+        sys.last_type, sys.last_value, sys.last_traceback = t, v, tb
+
         self._get_output_printer().display_exception(
             e,
             highlight=self.enable_syntax_highlighting,