bpo-42848: remove recursion from TracebackException (GH-24158)
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 4e008bc..aef37c9 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -481,39 +481,10 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
# permit backwards compat with the existing API, otherwise we
# need stub thunk objects just to glue it together.
# Handle loops in __cause__ or __context__.
+ is_recursive_call = _seen is not None
if _seen is None:
_seen = set()
_seen.add(id(exc_value))
- # Gracefully handle (the way Python 2.4 and earlier did) the case of
- # being called with no type or value (None, None, None).
- if (exc_value and exc_value.__cause__ is not None
- and id(exc_value.__cause__) not in _seen):
- cause = TracebackException(
- type(exc_value.__cause__),
- exc_value.__cause__,
- exc_value.__cause__.__traceback__,
- limit=limit,
- lookup_lines=False,
- capture_locals=capture_locals,
- _seen=_seen)
- else:
- cause = None
- if (exc_value and exc_value.__context__ is not None
- and id(exc_value.__context__) not in _seen):
- context = TracebackException(
- type(exc_value.__context__),
- exc_value.__context__,
- exc_value.__context__.__traceback__,
- limit=limit,
- lookup_lines=False,
- capture_locals=capture_locals,
- _seen=_seen)
- else:
- context = None
- self.__cause__ = cause
- self.__context__ = context
- self.__suppress_context__ = \
- exc_value.__suppress_context__ if exc_value else False
# TODO: locals.
self.stack = StackSummary.extract(
walk_tb(exc_traceback), limit=limit, lookup_lines=lookup_lines,
@@ -532,6 +503,45 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
self.msg = exc_value.msg
if lookup_lines:
self._load_lines()
+ self.__suppress_context__ = \
+ exc_value.__suppress_context__ if exc_value else False
+
+ # Convert __cause__ and __context__ to `TracebackExceptions`s, use a
+ # queue to avoid recursion (only the top-level call gets _seen == None)
+ if not is_recursive_call:
+ queue = [(self, exc_value)]
+ while queue:
+ te, e = queue.pop()
+ if (e and e.__cause__ is not None
+ and id(e.__cause__) not in _seen):
+ cause = TracebackException(
+ type(e.__cause__),
+ e.__cause__,
+ e.__cause__.__traceback__,
+ limit=limit,
+ lookup_lines=lookup_lines,
+ capture_locals=capture_locals,
+ _seen=_seen)
+ else:
+ cause = None
+ if (e and e.__context__ is not None
+ and id(e.__context__) not in _seen):
+ context = TracebackException(
+ type(e.__context__),
+ e.__context__,
+ e.__context__.__traceback__,
+ limit=limit,
+ lookup_lines=lookup_lines,
+ capture_locals=capture_locals,
+ _seen=_seen)
+ else:
+ context = None
+ te.__cause__ = cause
+ te.__context__ = context
+ if cause:
+ queue.append((te.__cause__, e.__cause__))
+ if context:
+ queue.append((te.__context__, e.__context__))
@classmethod
def from_exception(cls, exc, *args, **kwargs):
@@ -542,10 +552,6 @@ def _load_lines(self):
"""Private API. force all lines in the stack to be loaded."""
for frame in self.stack:
frame.line
- if self.__context__:
- self.__context__._load_lines()
- if self.__cause__:
- self.__cause__._load_lines()
def __eq__(self, other):
if isinstance(other, TracebackException):
@@ -622,15 +628,32 @@ def format(self, *, chain=True):
The message indicating which exception occurred is always the last
string in the output.
"""
- if chain:
- if self.__cause__ is not None:
- yield from self.__cause__.format(chain=chain)
- yield _cause_message
- elif (self.__context__ is not None and
- not self.__suppress_context__):
- yield from self.__context__.format(chain=chain)
- yield _context_message
- if self.stack:
- yield 'Traceback (most recent call last):\n'
- yield from self.stack.format()
- yield from self.format_exception_only()
+
+ output = []
+ exc = self
+ while exc:
+ if chain:
+ if exc.__cause__ is not None:
+ chained_msg = _cause_message
+ chained_exc = exc.__cause__
+ elif (exc.__context__ is not None and
+ not exc.__suppress_context__):
+ chained_msg = _context_message
+ chained_exc = exc.__context__
+ else:
+ chained_msg = None
+ chained_exc = None
+
+ output.append((chained_msg, exc))
+ exc = chained_exc
+ else:
+ output.append((None, exc))
+ exc = None
+
+ for msg, exc in reversed(output):
+ if msg is not None:
+ yield msg
+ if exc.stack:
+ yield 'Traceback (most recent call last):\n'
+ yield from exc.stack.format()
+ yield from exc.format_exception_only()