get exceptions working on Py3.11+

previously exceptions were parsed line by line, however
3.11 introduced https://docs.python.org/3/whatsnew/3.11.html#whatsnew311-pep657
which means that exception line numbers and traceback skip offsets
no longer line up.

Rather than inspect the source code this change introduces an
extra frame in `def _invoke_callback` that can be detected
by walking the traceback and finding its code object.

Author: graingert-coef

dash/_callback.py

@@ -35,6 +35,10 @@
 from ._callback_context import context_value
 
 
+def _invoke_callback(func, *args, **kwargs):  # used to mark the frame for the debugger
+    return func(*args, **kwargs)  # %% callback invoked %%
+
+
 class NoUpdate:
     def to_plotly_json(self):  # pylint: disable=no-self-use
         return {"_dash_no_update": "_dash_no_update"}
@@ -438,8 +442,7 @@ def add_context(*args, **kwargs):
                 if output_value is callback_manager.UNDEFINED:
                     return to_json(response)
             else:
-                # don't touch the comment on the next line - used by debugger
-                output_value = func(*func_args, **func_kwargs)  # %% callback invoked %%
+                output_value = _invoke_callback(func, *func_args, **func_kwargs)
 
             if NoUpdate.is_no_update(output_value):
                 raise PreventUpdate

dash/_jupyter.py

@@ -8,7 +8,6 @@
 import sys
 import threading
 import time
-import traceback
 
 from typing_extensions import Literal
 
@@ -37,12 +36,16 @@
 
 
 def _get_skip(error: Exception):
-    tb = traceback.format_exception(type(error), error, error.__traceback__)
-    skip = 0
-    for i, line in enumerate(tb):
-        if "%% callback invoked %%" in line:
-            skip = i + 1
-            break
+    from dash._callback import _invoke_callback  # pylint: disable=import-outside-toplevel
+
+    tb = error.__traceback__
+    skip = 1
+    while tb.tb_next is not None:
+        skip += 1
+        tb = tb.tb_next
+        if tb.tb_frame.f_code is _invoke_callback.__code__:
+            return skip
+
     return skip
 
 

dash/dash.py

@@ -146,32 +146,40 @@ def _get_traceback(secret, error: Exception):
     except ImportError:
         tbtools = None
 
-    def _get_skip(text, divider=2):
-        skip = 0
-        for i, line in enumerate(text):
-            if "%% callback invoked %%" in line:
-                skip = int((i + 1) / divider)
-                break
+    def _get_skip(error):
+        from dash._callback import _invoke_callback  # pylint: disable=import-outside-toplevel
+
+        tb = error.__traceback__
+        skip = 1
+        while tb.tb_next is not None:
+            skip += 1
+            tb = tb.tb_next
+            if tb.tb_frame.f_code is _invoke_callback.__code__:
+                return skip
+
         return skip
 
+    def _do_skip(error):
+        from dash._callback import _invoke_callback  # pylint: disable=import-outside-toplevel
+
+        tb = error.__traceback__
+        while tb.tb_next is not None:
+            if tb.tb_frame.f_code is _invoke_callback.__code__:
+                return tb.tb_next
+            tb = tb.tb_next
+        return error.__traceback__
+
     # werkzeug<2.1.0
     if hasattr(tbtools, "get_current_traceback"):
-        tb = tbtools.get_current_traceback()
-        skip = _get_skip(tb.plaintext.splitlines())
-        return tbtools.get_current_traceback(skip=skip).render_full()
+        return tbtools.get_current_traceback(skip=_get_skip(error)).render_full()
 
     if hasattr(tbtools, "DebugTraceback"):
-        tb = tbtools.DebugTraceback(error)  # pylint: disable=no-member
-        skip = _get_skip(tb.render_traceback_text().splitlines())
-
         # pylint: disable=no-member
-        return tbtools.DebugTraceback(error, skip=skip).render_debugger_html(
-            True, secret, True
-        )
+        return tbtools.DebugTraceback(
+            error, skip=_get_skip(error)
+        ).render_debugger_html(True, secret, True)
 
-    tb = traceback.format_exception(type(error), error, error.__traceback__)
-    skip = _get_skip(tb, 1)
-    return tb[0] + "".join(tb[skip:])
+    return "".join(traceback.format_exception(type(error), error, _do_skip(error)))
 
 
 # Singleton signal to not update an output, alternative to PreventUpdate