implement chained exception tracebacks
patch from Antoine Pitrou #3112
diff --git a/Lib/test/test_raise.py b/Lib/test/test_raise.py
index 3072c14..ba9cfc5 100644
--- a/Lib/test/test_raise.py
+++ b/Lib/test/test_raise.py
@@ -278,6 +278,30 @@
else:
self.fail("No exception raised")
+ def test_cycle_broken(self):
+ # Self-cycles (when re-raising a caught exception) are broken
+ try:
+ try:
+ 1/0
+ except ZeroDivisionError as e:
+ raise e
+ except ZeroDivisionError as e:
+ self.failUnless(e.__context__ is None, e.__context__)
+
+ def test_reraise_cycle_broken(self):
+ # Non-trivial context cycles (through re-raising a previous exception)
+ # are broken too.
+ try:
+ try:
+ xyzzy
+ except NameError as a:
+ try:
+ 1/0
+ except ZeroDivisionError:
+ raise a
+ except NameError as e:
+ self.failUnless(e.__context__.__context__ is None)
+
class TestRemovedFunctionality(unittest.TestCase):
def test_tuples(self):
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 3f89e6a..3f69e5e 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -1,10 +1,11 @@
"""Test cases for traceback module"""
-from _testcapi import traceback_print
+from _testcapi import traceback_print, exception_print
from io import StringIO
import sys
import unittest
-from test.support import run_unittest, is_jython, Error
+import re
+from test.support import run_unittest, is_jython, Error, captured_output
import traceback
@@ -19,7 +20,7 @@
raise Error("unable to create test traceback string")
-class TracebackCases(unittest.TestCase):
+class SyntaxTracebackCases(unittest.TestCase):
# For now, a very minimal set of tests. I want to be sure that
# formatting of SyntaxErrors works based on changes for 2.1.
@@ -99,12 +100,135 @@
banner, location, source_line = tb_lines
self.assert_(banner.startswith('Traceback'))
self.assert_(location.startswith(' File'))
- self.assert_(source_line.startswith('raise'))
+ self.assert_(source_line.startswith(' raise'))
+
+
+cause_message = (
+ "\nThe above exception was the direct cause "
+ "of the following exception:\n\n")
+
+context_message = (
+ "\nDuring handling of the above exception, "
+ "another exception occurred:\n\n")
+
+boundaries = re.compile(
+ '(%s|%s)' % (re.escape(cause_message), re.escape(context_message)))
+
+
+class BaseExceptionReportingTests:
+
+ def get_exception(self, exception_or_callable):
+ if isinstance(exception_or_callable, Exception):
+ return exception_or_callable
+ try:
+ exception_or_callable()
+ except Exception as e:
+ return e
+
+ def zero_div(self):
+ 1/0 # In zero_div
+
+ def check_zero_div(self, msg):
+ lines = msg.splitlines()
+ self.assert_(lines[-3].startswith(' File'))
+ self.assert_('1/0 # In zero_div' in lines[-2], lines[-2])
+ self.assert_(lines[-1].startswith('ZeroDivisionError'), lines[-1])
+
+ def test_simple(self):
+ try:
+ 1/0 # Marker
+ except ZeroDivisionError as _:
+ e = _
+ lines = self.get_report(e).splitlines()
+ self.assertEquals(len(lines), 4)
+ self.assert_(lines[0].startswith('Traceback'))
+ self.assert_(lines[1].startswith(' File'))
+ self.assert_('1/0 # Marker' in lines[2])
+ self.assert_(lines[3].startswith('ZeroDivisionError'))
+
+ def test_cause(self):
+ def inner_raise():
+ try:
+ self.zero_div()
+ except ZeroDivisionError as e:
+ raise KeyError from e
+ def outer_raise():
+ inner_raise() # Marker
+ blocks = boundaries.split(self.get_report(outer_raise))
+ self.assertEquals(len(blocks), 3)
+ self.assertEquals(blocks[1], cause_message)
+ self.check_zero_div(blocks[0])
+ self.assert_('inner_raise() # Marker' in blocks[2])
+
+ def test_context(self):
+ def inner_raise():
+ try:
+ self.zero_div()
+ except ZeroDivisionError:
+ raise KeyError
+ def outer_raise():
+ inner_raise() # Marker
+ blocks = boundaries.split(self.get_report(outer_raise))
+ self.assertEquals(len(blocks), 3)
+ self.assertEquals(blocks[1], context_message)
+ self.check_zero_div(blocks[0])
+ self.assert_('inner_raise() # Marker' in blocks[2])
+
+ def test_cause_recursive(self):
+ def inner_raise():
+ try:
+ try:
+ self.zero_div()
+ except ZeroDivisionError as e:
+ z = e
+ raise KeyError from e
+ except KeyError as e:
+ raise z from e
+ def outer_raise():
+ inner_raise() # Marker
+ blocks = boundaries.split(self.get_report(outer_raise))
+ self.assertEquals(len(blocks), 3)
+ self.assertEquals(blocks[1], cause_message)
+ # The first block is the KeyError raised from the ZeroDivisionError
+ self.assert_('raise KeyError from e' in blocks[0])
+ self.assert_('1/0' not in blocks[0])
+ # The second block (apart from the boundary) is the ZeroDivisionError
+ # re-raised from the KeyError
+ self.assert_('inner_raise() # Marker' in blocks[2])
+ self.check_zero_div(blocks[2])
+
+
+
+class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
+ #
+ # This checks reporting through the 'traceback' module, with both
+ # format_exception() and print_exception().
+ #
+
+ def get_report(self, e):
+ e = self.get_exception(e)
+ s = ''.join(
+ traceback.format_exception(type(e), e, e.__traceback__))
+ with captured_output("stderr") as sio:
+ traceback.print_exception(type(e), e, e.__traceback__)
+ self.assertEquals(sio.getvalue(), s)
+ return s
+
+
+class CExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
+ #
+ # This checks built-in reporting by the interpreter.
+ #
+
+ def get_report(self, e):
+ e = self.get_exception(e)
+ with captured_output("stderr") as s:
+ exception_print(e)
+ return s.getvalue()
def test_main():
- run_unittest(TracebackCases, TracebackFormatTests)
-
+ run_unittest(__name__)
if __name__ == "__main__":
test_main()
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):