implement chained exception tracebacks
patch from Antoine Pitrou #3112
diff --git a/Lib/traceback.py b/Lib/traceback.py
index fb1c5ad..b7130d8 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -3,6 +3,7 @@
import linecache
import sys
import types
+import itertools
__all__ = ['extract_stack', 'extract_tb', 'format_exception',
'format_exception_only', 'format_list', 'format_stack',
@@ -107,7 +108,32 @@
return list
-def print_exception(etype, value, tb, limit=None, file=None):
+_cause_message = (
+ "\nThe above exception was the direct cause "
+ "of the following exception:\n")
+
+_context_message = (
+ "\nDuring handling of the above exception, "
+ "another exception occurred:\n")
+
+def _iter_chain(exc, custom_tb=None, seen=None):
+ if seen is None:
+ seen = set()
+ seen.add(exc)
+ its = []
+ cause = exc.__cause__
+ context = exc.__context__
+ if cause is not None and cause not in seen:
+ its.append(_iter_chain(cause, None, seen))
+ its.append([(_cause_message, None)])
+ if context is not None and context is not cause and context not in seen:
+ its.append(_iter_chain(context, None, seen))
+ its.append([(_context_message, None)])
+ its.append([(exc, custom_tb or exc.__traceback__)])
+ return itertools.chain(*its)
+
+
+def print_exception(etype, value, tb, limit=None, file=None, chain=True):
"""Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
This differs from print_tb() in the following ways: (1) if
@@ -120,15 +146,23 @@
"""
if file is None:
file = sys.stderr
- if tb:
- _print(file, 'Traceback (most recent call last):')
- print_tb(tb, limit, file)
- lines = format_exception_only(etype, value)
- for line in lines[:-1]:
- _print(file, line, ' ')
- _print(file, lines[-1], '')
+ if chain:
+ values = _iter_chain(value, tb)
+ else:
+ values = [(value, tb)]
+ for value, tb in values:
+ if isinstance(value, str):
+ _print(file, value)
+ continue
+ if tb:
+ _print(file, 'Traceback (most recent call last):')
+ print_tb(tb, limit, file)
+ lines = format_exception_only(type(value), value)
+ for line in lines[:-1]:
+ _print(file, line, ' ')
+ _print(file, lines[-1], '')
-def format_exception(etype, value, tb, limit = None):
+def format_exception(etype, value, tb, limit=None, chain=True):
"""Format a stack trace and the exception information.
The arguments have the same meaning as the corresponding arguments
@@ -137,12 +171,19 @@
these lines are concatenated and printed, exactly the same text is
printed as does print_exception().
"""
- if tb:
- list = ['Traceback (most recent call last):\n']
- list = list + format_tb(tb, limit)
+ list = []
+ if chain:
+ values = _iter_chain(value, tb)
else:
- list = []
- list = list + format_exception_only(etype, value)
+ values = [(value, tb)]
+ for value, tb in values:
+ if isinstance(value, str):
+ list.append(value + '\n')
+ continue
+ if tb:
+ list.append('Traceback (most recent call last):\n')
+ list.extend(format_tb(tb, limit))
+ list.extend(format_exception_only(type(value), value))
return list
def format_exception_only(etype, value):
@@ -208,33 +249,34 @@
return '<unprintable %s object>' % type(value).__name__
-def print_exc(limit=None, file=None):
+def print_exc(limit=None, file=None, chain=True):
"""Shorthand for 'print_exception(*sys.exc_info(), limit, file)'."""
if file is None:
file = sys.stderr
try:
etype, value, tb = sys.exc_info()
- print_exception(etype, value, tb, limit, file)
+ print_exception(etype, value, tb, limit, file, chain)
finally:
etype = value = tb = None
-def format_exc(limit=None):
+def format_exc(limit=None, chain=True):
"""Like print_exc() but return a string."""
try:
etype, value, tb = sys.exc_info()
- return ''.join(format_exception(etype, value, tb, limit))
+ return ''.join(
+ format_exception(etype, value, tb, limit, chain))
finally:
etype = value = tb = None
-def print_last(limit=None, file=None):
+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 file is None:
file = sys.stderr
print_exception(sys.last_type, sys.last_value, sys.last_traceback,
- limit, file)
+ limit, file, chain)
def print_stack(f=None, limit=None, file=None):