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Original file line number	Diff line number	Diff line change
Expand Up		@@ -175,8 +175,8 @@ slightly different way:

		.. function:: pm()

		Enter post-mortem debugging of the traceback found in
		:data:`sys.last_traceback`.
		Enter post-mortem debugging of the exception found in
		:data:`sys.last_exc`.


		The ``run*`` functions and :func:`set_trace` are aliases for instantiating the
Expand Down Expand Up		@@ -639,6 +639,55 @@ can be overridden by the local file.

		Print the return value for the last return of the current function.

		.. pdbcommand:: exceptions [excnumber]
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		List or jump between chained exceptions.

		When using ``pdb.pm()`` or ``Pdb.post_mortem(...)`` with a chained exception
		instead of a traceback, it allows the user to move between the
		chained exceptions using ``exceptions`` command to list exceptions, and
		``exception <number>`` to switch to that exception.
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		Example::

		def out():
		try:
		middle()
		except Exception as e:
		raise ValueError("reraise middle() error") from e

		def middle():
		try:
		return inner(0)
		except Exception as e:
		raise ValueError("Middle fail")

		def inner(x):
		1 / x

		out()

		calling ``pdb.pm()`` will allow to move between exceptions::

		> example.py(5)out()
		-> raise ValueError("reraise middle() error") from e

		(Pdb) exceptions
		0 ZeroDivisionError('division by zero')
		1 ValueError('Middle fail')
		> 2 ValueError('reraise middle() error')

		(Pdb) exceptions 0
		> example.py(16)inner()
		-> 1 / x

		(Pdb) up
		> example.py(10)middle()
		-> return inner(0)

		.. versionadded:: 3.13

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		.. rubric:: Footnotes

		.. [1] Whether a frame is considered to originate in a certain module
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7 changes: 7 additions & 0 deletions 7 Doc/whatsnew/3.13.rst

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -158,6 +158,13 @@ pathlib
		:meth:`~pathlib.Path.is_dir`.
		(Contributed by Barney Gale in :gh:`77609` and :gh:`105793`.)

		pdb
		---

		* Add ability to move between chained exceptions during post mortem debugging in :func:`~pdb.pm` using
		the new ``exceptions [exc_number]`` command for Pdb. (Contributed by Matthias
		Bussonnier in :gh:`106676`.)

		sqlite3
		-------

Expand Down

142 changes: 124 additions & 18 deletions 142 Lib/pdb.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -85,6 +85,7 @@
		import traceback
		import linecache

		from contextlib import contextmanager
		from typing import Union


Expand Down Expand Up		@@ -205,10 +206,15 @@ def namespace(self):
		# line_prefix = ': ' # Use this to get the old situation back
		line_prefix = '\n-> ' # Probably a better default

		class Pdb(bdb.Bdb, cmd.Cmd):


		class Pdb(bdb.Bdb, cmd.Cmd):
		_previous_sigint_handler = None

		# Limit the maximum depth of chained exceptions, we should be handling cycles,
		# but in case there are recursions, we stop at 999.
		MAX_CHAINED_EXCEPTION_DEPTH = 999

		def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
		nosigint=False, readrc=True):
		bdb.Bdb.__init__(self, skip=skip)
Expand Down Expand Up		@@ -256,6 +262,9 @@ def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
		self.commands_bnum = None # The breakpoint number for which we are
		# defining a list

		self._chained_exceptions = tuple()
		self._chained_exception_index = 0

		def sigint_handler(self, signum, frame):
		if self.allow_kbdint:
		raise KeyboardInterrupt
Expand Down Expand Up		@@ -414,7 +423,64 @@ def preloop(self):
		self.message('display %s: %r [old: %r]' %
		(expr, newvalue, oldvalue))

		def interaction(self, frame, traceback):
		def _get_tb_and_exceptions(self, tb_or_exc):
		"""
		Given a tracecack or an exception, return a tuple of chained exceptions
		and current traceback to inspect.

		This will deal with selecting the right ``__cause__`` or ``__context__``
		as well as handling cycles, and return a flattened list of exceptions we
		can jump to with do_exceptions.

		"""
		_exceptions = []
		if isinstance(tb_or_exc, BaseException):
		traceback, current = tb_or_exc.__traceback__, tb_or_exc

		while current is not None:
		if current in _exceptions:
		break
		_exceptions.append(current)
		if current.__cause__ is not None:
		current = current.__cause__
		elif (
		current.__context__ is not None and not current.__suppress_context__
		):
		current = current.__context__

		if len(_exceptions) >= self.MAX_CHAINED_EXCEPTION_DEPTH:
		self.message(
		f"More than {self.MAX_CHAINED_EXCEPTION_DEPTH}"
		" chained exceptions found, not all exceptions"
		"will be browsable with `exceptions`."
		)
		break
		else:
		traceback = tb_or_exc
		return tuple(reversed(_exceptions)), traceback

		@contextmanager
		def _hold_exceptions(self, exceptions):
		"""
		Context manager to ensure proper cleaning of exceptions references

		When given a chained exception instead of a traceback,
		pdb may hold references to many objects which may leak memory.

		We use this context manager to make sure everything is properly cleaned

		"""
		try:
		self._chained_exceptions = exceptions
		self._chained_exception_index = len(exceptions) - 1
		yield
		finally:
		# we can't put those in forget as otherwise they would
		# be cleared on exception change
		self._chained_exceptions = tuple()
		self._chained_exception_index = 0

		def interaction(self, frame, tb_or_exc):
		# Restore the previous signal handler at the Pdb prompt.
		if Pdb._previous_sigint_handler:
		try:
Expand All		@@ -423,14 +489,17 @@ def interaction(self, frame, traceback):
		pass
		else:
		Pdb._previous_sigint_handler = None
		if self.setup(frame, traceback):
		# no interaction desired at this time (happens if .pdbrc contains
		# a command like "continue")

		_chained_exceptions, tb = self._get_tb_and_exceptions(tb_or_exc)
		with self._hold_exceptions(_chained_exceptions):
		if self.setup(frame, tb):
		# no interaction desired at this time (happens if .pdbrc contains
		# a command like "continue")
		self.forget()
		return
		self.print_stack_entry(self.stack[self.curindex])
		self._cmdloop()
		self.forget()
		return
		self.print_stack_entry(self.stack[self.curindex])
		self._cmdloop()
		self.forget()

		def displayhook(self, obj):
		"""Custom displayhook for the exec in default(), which prevents
Expand Down Expand Up		@@ -1073,6 +1142,44 @@ def _select_frame(self, number):
		self.print_stack_entry(self.stack[self.curindex])
		self.lineno = None

		def do_exceptions(self, arg):
		"""exceptions [number]

		List or change current exception in an exception chain.

		Without arguments, list all the current exception in the exception
		chain. Exceptions will be numbered, with the current exception indicated
		with an arrow.

		If given an integer as argument, switch to the exception at that index.
		"""
		if not self._chained_exceptions:
		self.message(
		"Did not find chained exceptions. To move between"
		" exceptions, pdb/post_mortem must be given an exception"
		" object rather than a traceback."
		)
		return
		if not arg:
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		for ix, exc in enumerate(self._chained_exceptions):
		prompt = ">" if ix == self._chained_exception_index else " "
		rep = repr(exc)
		if len(rep) > 80:
		rep = rep[:77] + "..."
		self.message(f"{prompt} {ix:>3} {rep}")
		else:
		try:
		number = int(arg)
		except ValueError:
		self.error("Argument must be an integer")
		return
		if 0 <= number < len(self._chained_exceptions):
		self._chained_exception_index = number
		self.setup(None, self._chained_exceptions[number].__traceback__)
		self.print_stack_entry(self.stack[self.curindex])
		else:
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		self.error("No exception with that number")

		def do_up(self, arg):
		"""u(p) [count]

Expand Down Expand Up		@@ -1890,11 +1997,15 @@ def set_trace(*, header=None):
		# Post-Mortem interface

		def post_mortem(t=None):
		"""Enter post-mortem debugging of the given traceback object.
		"""Enter post-mortem debugging of the given traceback, or exception
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		object.

		If no traceback is given, it uses the one of the exception that is
		currently being handled (an exception must be being handled if the
		default is to be used).

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		If `t` is an exception object, the `exceptions` command makes it possible to
		list and inspect its chained exceptions (if any).
		"""
		# handling the default
		if t is None:
Expand All		@@ -1911,12 +2022,8 @@ def post_mortem(t=None):
		p.interaction(None, t)

		def pm():
		"""Enter post-mortem debugging of the traceback found in sys.last_traceback."""
		if hasattr(sys, 'last_exc'):
		tb = sys.last_exc.__traceback__
		else:
		tb = sys.last_traceback
		post_mortem(tb)
		"""Enter post-mortem debugging of the traceback found in sys.last_exc."""
		post_mortem(sys.last_exc)


		# Main program for testing
Expand Down Expand Up		@@ -1996,8 +2103,7 @@ def main():
		traceback.print_exc()
		print("Uncaught exception. Entering post mortem debugging")
		print("Running 'cont' or 'step' will restart the program")
		t = e.__traceback__
		pdb.interaction(None, t)
		pdb.interaction(None, e)
		print("Post mortem debugger finished. The " + target +
		" will be restarted")

Expand Down

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