[Python-modules-commits] [python-django] 10/12: Fix #25761 -- re-raised exceptions need __cause__.__traceback__

[Raphaël Hertzog]

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hertzog pushed a commit to branch debian/master
in repository python-django.

commit 550694a2186bb09ebdeac0c14ee50c636ef0f763
Author: Raphaël Hertzog <hertzog at debian.org>
Date:   Wed Nov 25 12:54:52 2015 +0100

    Fix #25761 -- re-raised exceptions need __cause__.__traceback__
    
    When Django re-raises an exception, it sets the __cause__ attribute even
    in Python 2, thus mimicking Python's 3 behaviour for "raise Foo from Bar".
    However Python 3 also ensures that all exceptions have a __traceback__
    attribute and thus the "traceback2" Python 2 module (backport of Python
    3's "traceback" module) relies on the fact that whenever you have a
    __cause__ attribute, the recorded exception also has a __traceback__
    attribute.
    
    This is breaking at least testtools which is using traceback2 (see
    https://github.com/testing-cabal/testtools/issues/162).
    
    This commit fixes this inconsistency by ensuring that Django sets
    the __traceback__ attribute on any exception stored in a __cause__
    attribute of a re-raised exception.
    
    Patch-Name: fix-25761-add-traceback-attribute.patch
---
 django/db/migrations/loader.py | 2 ++
 django/db/utils.py             | 2 ++
 django/utils/timezone.py       | 2 ++
 docs/ref/exceptions.txt        | 4 +++-
 4 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/django/db/migrations/loader.py b/django/db/migrations/loader.py
index 310a4d0..7ef5e9d 100644
--- a/django/db/migrations/loader.py
+++ b/django/db/migrations/loader.py
@@ -272,6 +272,8 @@ class MigrationLoader(object):
                         ),
                         missing)
                     exc_value.__cause__ = exc
+                    if not hasattr(exc, '__traceback__'):
+                        exc.__traceback__ = sys.exc_info()[2]
                     six.reraise(NodeNotFoundError, exc_value, sys.exc_info()[2])
             raise exc
 
diff --git a/django/db/utils.py b/django/db/utils.py
index 380a4b9..73ed6a6 100644
--- a/django/db/utils.py
+++ b/django/db/utils.py
@@ -88,6 +88,8 @@ class DatabaseErrorWrapper(object):
             if issubclass(exc_type, db_exc_type):
                 dj_exc_value = dj_exc_type(*exc_value.args)
                 dj_exc_value.__cause__ = exc_value
+                if not hasattr(exc_value, '__traceback__'):
+                    exc_value.__traceback__ = traceback
                 # Only set the 'errors_occurred' flag for errors that may make
                 # the connection unusable.
                 if dj_exc_type not in (DataError, IntegrityError):
diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 70fd5e3..205cac4 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -146,6 +146,8 @@ class LocalTimezone(ReferenceLocalTimezone):
             exc_value = exc_type(
                 "Unsupported value: %r. You should install pytz." % dt)
             exc_value.__cause__ = exc
+            if not hasattr(exc, '__traceback__'):
+                exc.__traceback__ = sys.exc_info()[2]
             six.reraise(exc_type, exc_value, sys.exc_info()[2])
 
 utc = pytz.utc if pytz else UTC()
diff --git a/docs/ref/exceptions.txt b/docs/ref/exceptions.txt
index 46a0c81..a16d352 100644
--- a/docs/ref/exceptions.txt
+++ b/docs/ref/exceptions.txt
@@ -201,7 +201,9 @@ As per :pep:`3134`, a ``__cause__`` attribute is set with the original
 (underlying) database exception, allowing access to any additional
 information provided. (Note that this attribute is available under
 both Python 2 and Python 3, although :pep:`3134` normally only applies
-to Python 3.)
+to Python 3. With Python 2, Django will also record the traceback in the
+``__traceback__`` attribute of the exception made available via
+``__cause__``.)
 
 .. exception:: models.ProtectedError
 

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