- Fixed bug where some exception re-raise scenarios would attach

the exception to itself as the "cause"; while the Python 3 interpreter
is OK with this, it could cause endless loops in iPython.
fixes #3625
- add tests for reraise, raise_from_cause
- raise_from_cause is the same on py2k/3k, use just one function

1 files changed, 12 insertions, 12 deletions

diff --git a/lib/sqlalchemy/util/compat.py b/lib/sqlalchemy/util/compat.py
index 25c88c662..737b8a087 100644
--- a/lib/sqlalchemy/util/compat.py
+++ b/lib/sqlalchemy/util/compat.py
@@ -177,27 +177,27 @@ from operator import attrgetter as dottedgetter
 if py3k:
     def reraise(tp, value, tb=None, cause=None):
         if cause is not None:
+            assert cause is not value, "Same cause emitted"
             value.__cause__ = cause
         if value.__traceback__ is not tb:
             raise value.with_traceback(tb)
         raise value
 
-    def raise_from_cause(exception, exc_info=None):
-        if exc_info is None:
-            exc_info = sys.exc_info()
-        exc_type, exc_value, exc_tb = exc_info
-        reraise(type(exception), exception, tb=exc_tb, cause=exc_value)
 else:
+    # not as nice as that of Py3K, but at least preserves
+    # the code line where the issue occurred
     exec("def reraise(tp, value, tb=None, cause=None):\n"
+         "    if cause is not None:\n"
+         "        assert cause is not value, 'Same cause emitted'\n"
          "    raise tp, value, tb\n")
 
-    def raise_from_cause(exception, exc_info=None):
-        # not as nice as that of Py3K, but at least preserves
-        # the code line where the issue occurred
-        if exc_info is None:
-            exc_info = sys.exc_info()
-        exc_type, exc_value, exc_tb = exc_info
-        reraise(type(exception), exception, tb=exc_tb)
+
+def raise_from_cause(exception, exc_info=None):
+    if exc_info is None:
+        exc_info = sys.exc_info()
+    exc_type, exc_value, exc_tb = exc_info
+    cause = exc_value if exc_value is not exception else None
+    reraise(type(exception), exception, tb=exc_tb, cause=cause)
 
 if py3k:
     exec_ = getattr(builtins, 'exec')