gh-102778: Add sys.last_exc, deprecate sys.last_type, sys.last_value,…

…sys.last_traceback (#102779)

Doc/library/sys.rst

@@ -1102,22 +1102,25 @@ always available.
 
    .. versionadded:: 3.5
 
+.. data:: last_exc
+
+   This variable is not always defined; it is set to the exception instance
+   when an exception is not handled and the interpreter prints an error message
+   and a stack traceback.  Its intended use is to allow an interactive user to
+   import a debugger module and engage in post-mortem debugging without having
+   to re-execute the command that caused the error.  (Typical use is
+   ``import pdb; pdb.pm()`` to enter the post-mortem debugger; see :mod:`pdb`
+   module for more information.)
+
+   .. versionadded:: 3.12
 
 .. data:: last_type
           last_value
           last_traceback
 
-   These three variables are not always defined; they are set when an exception is
-   not handled and the interpreter prints an error message and a stack traceback.
-   Their intended use is to allow an interactive user to import a debugger module
-   and engage in post-mortem debugging without having to re-execute the command
-   that caused the error.  (Typical use is ``import pdb; pdb.pm()`` to enter the
-   post-mortem debugger; see :mod:`pdb` module for
-   more information.)
-
-   The meaning of the variables is the same as that of the return values from
-   :func:`exc_info` above.
-
+   These three variables are deprecated; use :data:`sys.last_exc` instead.
+   They hold the legacy representation of ``sys.last_exc``, as returned
+   from :func:`exc_info` above.
 
 .. data:: maxsize
 

Doc/whatsnew/3.12.rst

@@ -397,6 +397,12 @@ sys
   with contributions from Gregory P. Smith [Google] and Mark Shannon
   in :gh:`96123`.)
 
+* Add :data:`sys.last_exc` which holds the last unhandled exception that
+  was raised (for post-mortem debugging use cases). Deprecate the
+  three fields that have the same information in its legacy form:
+  :data:`sys.last_type`, :data:`sys.last_value` and :data:`sys.last_traceback`.
+  (Contributed by Irit Katriel in :gh:`102778`.)
+
 
 Optimizations
 =============
@@ -488,6 +494,10 @@ Deprecated
   contain the creation time, which is also available in the new ``st_birthtime``
   field. (Contributed by Steve Dower in :gh:`99726`.)
 
+* The :data:`sys.last_type`, :data:`sys.last_value` and :data:`sys.last_traceback`
+  fields are deprecated. Use :data:`sys.last_exc` instead.
+  (Contributed by Irit Katriel in :gh:`102778`.)
+
 Pending Removal in Python 3.13
 ------------------------------
 

Include/internal/pycore_global_strings.h

@@ -481,6 +481,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(kw2)
         STRUCT_FOR_ID(lambda)
         STRUCT_FOR_ID(last)
+        STRUCT_FOR_ID(last_exc)
         STRUCT_FOR_ID(last_node)
         STRUCT_FOR_ID(last_traceback)
         STRUCT_FOR_ID(last_type)

Lib/code.py

@@ -106,6 +106,7 @@ def showsyntaxerror(self, filename=None):
 
         """
         type, value, tb = sys.exc_info()
+        sys.last_exc = value
         sys.last_type = type
         sys.last_value = value
         sys.last_traceback = tb
@@ -119,7 +120,7 @@ def showsyntaxerror(self, filename=None):
             else:
                 # Stuff in the right filename
                 value = SyntaxError(msg, (filename, lineno, offset, line))
-                sys.last_value = value
+                sys.last_exc = sys.last_value = value
         if sys.excepthook is sys.__excepthook__:
             lines = traceback.format_exception_only(type, value)
             self.write(''.join(lines))
@@ -138,6 +139,7 @@ def showtraceback(self):
         """
         sys.last_type, sys.last_value, last_tb = ei = sys.exc_info()
         sys.last_traceback = last_tb
+        sys.last_exc = ei[1]
         try:
             lines = traceback.format_exception(ei[0], ei[1], last_tb.tb_next)
             if sys.excepthook is sys.__excepthook__:

Lib/dis.py

@@ -118,7 +118,10 @@ def distb(tb=None, *, file=None, show_caches=False, adaptive=False):
     """Disassemble a traceback (default: last traceback)."""
     if tb is None:
         try:
-            tb = sys.last_traceback
+            if hasattr(sys, 'last_exc'):
+                tb = sys.last_exc.__traceback__
+            else:
+                tb = sys.last_traceback
         except AttributeError:
             raise RuntimeError("no last traceback to disassemble") from None
         while tb.tb_next: tb = tb.tb_next

Lib/idlelib/idle_test/test_stackviewer.py

@@ -19,6 +19,7 @@ def setUpClass(cls):
         except NameError:
             svs.last_type, svs.last_value, svs.last_traceback = (
                 sys.exc_info())
+            svs.last_exc = svs.last_value
 
         requires('gui')
         cls.root = Tk()
@@ -27,7 +28,7 @@ def setUpClass(cls):
     @classmethod
     def tearDownClass(cls):
         svs = stackviewer.sys
-        del svs.last_traceback, svs.last_type, svs.last_value
+        del svs.last_exc, svs.last_traceback, svs.last_type, svs.last_value
 
         cls.root.update_idletasks()
 ##        for id in cls.root.tk.call('after', 'info'):

Lib/idlelib/pyshell.py

@@ -1367,11 +1367,14 @@ def open_stack_viewer(self, event=None):
         if self.interp.rpcclt:
             return self.interp.remote_stack_viewer()
         try:
-            sys.last_traceback
+            if hasattr(sys, 'last_exc'):
+                sys.last_exc.__traceback__
+            else:
+                sys.last_traceback
         except:
             messagebox.showerror("No stack trace",
                 "There is no stack trace yet.\n"
-                "(sys.last_traceback is not defined)",
+                "(sys.last_exc and sys.last_traceback are not defined)",
                 parent=self.text)
             return
         from idlelib.stackviewer import StackBrowser

Lib/idlelib/run.py

@@ -239,6 +239,7 @@ def print_exception():
     efile = sys.stderr
     typ, val, tb = excinfo = sys.exc_info()
     sys.last_type, sys.last_value, sys.last_traceback = excinfo
+    sys.last_exc = val
     seen = set()
 
     def print_exc(typ, exc, tb):
@@ -629,6 +630,7 @@ def stackviewer(self, flist_oid=None):
             flist = self.rpchandler.get_remote_proxy(flist_oid)
         while tb and tb.tb_frame.f_globals["__name__"] in ["rpc", "run"]:
             tb = tb.tb_next
+        sys.last_exc = val
         sys.last_type = typ
         sys.last_value = val
         item = stackviewer.StackTreeItem(flist, tb)

Lib/idlelib/stackviewer.py

@@ -27,7 +27,10 @@ def __init__(self, flist=None, tb=None):
 
     def get_stack(self, tb):
         if tb is None:
-            tb = sys.last_traceback
+            if hasattr(sys, 'last_exc'):
+                tb = sys.last_exc.__traceback__
+            else:
+                tb = sys.last_traceback
         stack = []
         if tb and tb.tb_frame is None:
             tb = tb.tb_next
@@ -37,11 +40,15 @@ def get_stack(self, tb):
         return stack
 
     def get_exception(self):
-        type = sys.last_type
-        value = sys.last_value
-        if hasattr(type, "__name__"):
-            type = type.__name__
-        s = str(type)
+        if hasattr(sys, 'last_exc'):
+            typ = type(sys.last_exc)
+            value = sys.last_exc
+        else:
+            typ = sys.last_type
+            value = sys.last_value
+        if hasattr(typ, "__name__"):
+            typ = typ.__name__
+        s = str(typ)
         if value is not None:
             s = s + ": " + str(value)
         return s
@@ -136,13 +143,15 @@ def _stack_viewer(parent):  # htest #
     except NameError:
         exc_type, exc_value, exc_tb = sys.exc_info()
     # inject stack trace to sys
+    sys.last_exc = exc_value
     sys.last_type = exc_type
     sys.last_value = exc_value
     sys.last_traceback = exc_tb
 
     StackBrowser(top, flist=flist, top=top, tb=exc_tb)
 
     # restore sys to original state
+    del sys.last_exc
     del sys.last_type
     del sys.last_value
     del sys.last_traceback

Lib/pdb.py

@@ -1739,7 +1739,11 @@ def post_mortem(t=None):
 
 def pm():
     """Enter post-mortem debugging of the traceback found in sys.last_traceback."""
-    post_mortem(sys.last_traceback)
+    if hasattr(sys, 'last_exc'):
+        tb = sys.last_exc.__traceback__
+    else:
+        tb = sys.last_traceback
+    post_mortem(tb)
 
 
 # Main program for testing

Lib/pydoc_data/topics.py

@@ -4799,7 +4799,7 @@
              'pdb.pm()\n'
              '\n'
              '   Enter post-mortem debugging of the traceback found in\n'
-             '   "sys.last_traceback".\n'
+             '   "sys.last_exc".\n'
              '\n'
              'The "run*" functions and "set_trace()" are aliases for '
              'instantiating\n'
@@ -13858,7 +13858,7 @@
           'if\n'
           '      the interpreter is interactive, it is also made available to '
           'the\n'
-          '      user as "sys.last_traceback".\n'
+          '      user as "sys.last_exc".\n'
           '\n'
           '      For explicitly created tracebacks, it is up to the creator '
           'of\n'

Lib/test/test_dis.py

@@ -1026,6 +1026,10 @@ def test_disassemble_try_finally(self):
         self.do_disassembly_test(_tryfinallyconst, dis_tryfinallyconst)
 
     def test_dis_none(self):
+        try:
+            del sys.last_exc
+        except AttributeError:
+            pass
         try:
             del sys.last_traceback
         except AttributeError:
@@ -1043,7 +1047,7 @@ def test_dis_traceback(self):
             1/0
         except Exception as e:
             tb = e.__traceback__
-            sys.last_traceback = tb
+            sys.last_exc = e
 
         tb_dis = self.get_disassemble_as_string(tb.tb_frame.f_code, tb.tb_lasti)
         self.do_disassembly_test(None, tb_dis, True)
@@ -1900,6 +1904,10 @@ def test_findlabels(self):
 
 class TestDisTraceback(DisTestBase):
     def setUp(self) -> None:
+        try:  # We need to clean up existing tracebacks
+            del sys.last_exc
+        except AttributeError:
+            pass
         try:  # We need to clean up existing tracebacks
             del sys.last_traceback
         except AttributeError:

Lib/test/test_ttk/test_extensions.py

@@ -45,7 +45,9 @@ def test_widget_destroy(self):
         # value which causes the tracing callback to be called and then
         # it tries calling instance attributes not yet defined.
         ttk.LabeledScale(self.root, variable=myvar)
-        if hasattr(sys, 'last_type'):
+        if hasattr(sys, 'last_exc'):
+            self.assertNotEqual(type(sys.last_exc), tkinter.TclError)
+        elif hasattr(sys, 'last_type'):
             self.assertNotEqual(sys.last_type, tkinter.TclError)
 
     def test_initialization(self):

Lib/tkinter/__init__.py

@@ -2400,6 +2400,7 @@ def report_callback_exception(self, exc, val, tb):
         should when sys.stderr is None."""
         import traceback
         print("Exception in Tkinter callback", file=sys.stderr)
+        sys.last_exc = val
         sys.last_type = exc
         sys.last_value = val
         sys.last_traceback = tb

Lib/traceback.py

@@ -179,20 +179,24 @@ def _safe_string(value, what, func=str):
 # --
 
 def print_exc(limit=None, file=None, chain=True):
-    """Shorthand for 'print_exception(*sys.exc_info(), limit, file)'."""
+    """Shorthand for 'print_exception(*sys.exc_info(), limit, file, chain)'."""
     print_exception(*sys.exc_info(), limit=limit, file=file, chain=chain)
 
 def format_exc(limit=None, chain=True):
     """Like print_exc() but return a string."""
     return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))
 
 def print_last(limit=None, file=None, chain=True):
-    """This is a shorthand for 'print_exception(sys.last_type,
-    sys.last_value, sys.last_traceback, limit, file)'."""
-    if not hasattr(sys, "last_type"):
+    """This is a shorthand for 'print_exception(sys.last_exc, limit, file, chain)'."""
+    if not hasattr(sys, "last_exc") and not hasattr(sys, "last_type"):
         raise ValueError("no last exception")
-    print_exception(sys.last_type, sys.last_value, sys.last_traceback,
-                    limit, file, chain)
+
+    if hasattr(sys, "last_exc"):
+        print_exception(sys.last_exc, limit, file, chain)
+    else:
+        print_exception(sys.last_type, sys.last_value, sys.last_traceback,
+                        limit, file, chain)
+
 
 #
 # Printing and Extracting Stacks.

Misc/NEWS.d/next/Core and Builtins/2023-03-17-13-43-34.gh-issue-102778.ANDv8I.rst

@@ -0,0 +1,3 @@
+Add :data:`sys.last_exc` and deprecate :data:`sys.last_type`, :data:`sys.last_value`
+and :data:`sys.last_traceback`,
+which hold the same information in its legacy form.

Python/pylifecycle.c

@@ -1304,7 +1304,7 @@ finalize_modules_delete_special(PyThreadState *tstate, int verbose)
 {
     // List of names to clear in sys
     static const char * const sys_deletes[] = {
-        "path", "argv", "ps1", "ps2",
+        "path", "argv", "ps1", "ps2", "last_exc",
         "last_type", "last_value", "last_traceback",
         "__interactivehook__",
         // path_hooks and path_importer_cache are cleared

Python/pythonrun.c

@@ -776,6 +776,10 @@ _PyErr_PrintEx(PyThreadState *tstate, int set_sys_last_vars)
     }
 
     if (set_sys_last_vars) {
+        if (_PySys_SetAttr(&_Py_ID(last_exc), exc) < 0) {
+            _PyErr_Clear(tstate);
+        }
+        /* Legacy version: */
         if (_PySys_SetAttr(&_Py_ID(last_type), typ) < 0) {
             _PyErr_Clear(tstate);
         }

Python/sysmodule.c

@@ -2670,11 +2670,13 @@ stderr -- standard error object; used for error messages\n\
   By assigning other file objects (or objects that behave like files)\n\
   to these, it is possible to redirect all of the interpreter's I/O.\n\
 \n\
+last_exc - the last uncaught exception\n\
+  Only available in an interactive session after a\n\
+  traceback has been printed.\n\
 last_type -- type of last uncaught exception\n\
 last_value -- value of last uncaught exception\n\
 last_traceback -- traceback of last uncaught exception\n\
-  These three are only available in an interactive session after a\n\
-  traceback has been printed.\n\
+  These three are the (deprecated) legacy representation of last_exc.\n\
 "
 )
 /* concatenating string here */