Fixed #18003 -- Preserved tracebacks when re-raising errors.

Thanks jrothenbuhler for draft patch, Konark Modi for updates.

django/contrib/admin/views/main.py

 import operator
+import sys
 import warnings
 from functools import reduce
 
@@ -173,7 +174,7 @@ class ChangeList(six.with_metaclass(RenameChangeListMethods)):
                                 lookup_needs_distinct(self.lookup_opts, key))
             return filter_specs, bool(filter_specs), lookup_params, use_distinct
         except FieldDoesNotExist as e:
-            raise IncorrectLookupParameters(e)
+            six.reraise(IncorrectLookupParameters, IncorrectLookupParameters(e), sys.exc_info()[2])
 
     def get_query_string(self, new_params=None, remove=None):
         if new_params is None: new_params = {}

django/contrib/gis/db/backends/oracle/introspection.py

 import cx_Oracle
+import sys
 from django.db.backends.oracle.introspection import DatabaseIntrospection
+from django.utils import six
 
 class OracleIntrospection(DatabaseIntrospection):
     # Associating any OBJECTVAR instances with GeometryField.  Of course,
@@ -17,8 +19,11 @@ class OracleIntrospection(DatabaseIntrospection):
                                (table_name.upper(), geo_col.upper()))
                 row = cursor.fetchone()
             except Exception as msg:
-                raise Exception('Could not find entry in USER_SDO_GEOM_METADATA corresponding to "%s"."%s"\n'
-                                'Error message: %s.' % (table_name, geo_col, msg))
+                new_msg = (
+                    'Could not find entry in USER_SDO_GEOM_METADATA '
+                    'corresponding to "%s"."%s"\n'
+                    'Error message: %s.') % (table_name, geo_col, msg)
+                six.reraise(Exception, Exception(new_msg), sys.exc_info()[2])
 
             # TODO: Research way to find a more specific geometry field type for
             # the column's contents.

django/contrib/gis/db/backends/spatialite/base.py

+import sys
 from ctypes.util import find_library
 from django.conf import settings
 
@@ -8,6 +9,7 @@ from django.contrib.gis.db.backends.spatialite.client import SpatiaLiteClient
 from django.contrib.gis.db.backends.spatialite.creation import SpatiaLiteCreation
 from django.contrib.gis.db.backends.spatialite.introspection import SpatiaLiteIntrospection
 from django.contrib.gis.db.backends.spatialite.operations import SpatiaLiteOperations
+from django.utils import six
 
 class DatabaseWrapper(SQLiteDatabaseWrapper):
     def __init__(self, *args, **kwargs):
@@ -50,7 +52,9 @@ class DatabaseWrapper(SQLiteDatabaseWrapper):
         try:
             cur.execute("SELECT load_extension(%s)", (self.spatialite_lib,))
         except Exception as msg:
-            raise ImproperlyConfigured('Unable to load the SpatiaLite library extension '
-                                       '"%s" because: %s' % (self.spatialite_lib, msg))
+            new_msg = (
+                'Unable to load the SpatiaLite library extension '
+                '"%s" because: %s') % (self.spatialite_lib, msg)
+            six.reraise(ImproperlyConfigured, ImproperlyConfigured(new_msg), sys.exc_info()[2])
         cur.close()
         return conn

django/contrib/gis/db/backends/spatialite/operations.py

 import re
+import sys
 from decimal import Decimal
 
 from django.contrib.gis.db.backends.base import BaseSpatialOperations
@@ -126,10 +127,11 @@ class SpatiaLiteOperations(DatabaseOperations, BaseSpatialOperations):
         try:
             version = self.spatialite_version_tuple()[1:]
         except Exception as msg:
-            raise ImproperlyConfigured('Cannot determine the SpatiaLite version for the "%s" '
-                                       'database (error was "%s").  Was the SpatiaLite initialization '
-                                       'SQL loaded on this database?' %
-                                       (self.connection.settings_dict['NAME'], msg))
+            new_msg = (
+                'Cannot determine the SpatiaLite version for the "%s" '
+                'database (error was "%s").  Was the SpatiaLite initialization '
+                'SQL loaded on this database?') % (self.connection.settings_dict['NAME'], msg)
+            six.reraise(ImproperlyConfigured, ImproperlyConfigured(new_msg), sys.exc_info()[2])
         if version < (2, 3, 0):
             raise ImproperlyConfigured('GeoDjango only supports SpatiaLite versions '
                                        '2.3.0 and above')

django/contrib/gis/utils/layermapping.py

@@ -429,7 +429,8 @@ class LayerMapping(object):
             # Creating the CoordTransform object
             return CoordTransform(self.source_srs, target_srs)
         except Exception as msg:
-            raise LayerMapError('Could not translate between the data source and model geometry: %s' % msg)
+            new_msg = 'Could not translate between the data source and model geometry: %s' % msg
+            six.reraise(LayerMapError, LayerMapError(new_msg), sys.exc_info()[2])
 
     def geometry_field(self):
         "Returns the GeometryField instance associated with the geographic column."

django/core/management/commands/flush.py

+import sys
 from optparse import make_option
 
 from django.conf import settings
@@ -8,6 +9,7 @@ from django.core.management.color import no_style
 from django.core.management.sql import sql_flush, emit_post_sync_signal
 from django.utils.importlib import import_module
 from django.utils.six.moves import input
+from django.utils import six
 
 
 class Command(NoArgsCommand):
@@ -62,13 +64,14 @@ Are you sure you want to do this?
                     for sql in sql_list:
                         cursor.execute(sql)
             except Exception as e:
-                raise CommandError("""Database %s couldn't be flushed. Possible reasons:
-  * The database isn't running or isn't configured correctly.
-  * At least one of the expected database tables doesn't exist.
-  * The SQL was invalid.
-Hint: Look at the output of 'django-admin.py sqlflush'. That's the SQL this command wasn't able to run.
-The full error: %s""" % (connection.settings_dict['NAME'], e))
-
+                new_msg = (
+                    "Database %s couldn't be flushed. Possible reasons:\n"
+                    "  * The database isn't running or isn't configured correctly.\n"
+                    "  * At least one of the expected database tables doesn't exist.\n"
+                    "  * The SQL was invalid.\n"
+                    "Hint: Look at the output of 'django-admin.py sqlflush'. That's the SQL this command wasn't able to run.\n"
+                    "The full error: %s") % (connection.settings_dict['NAME'], e)
+                six.reraise(CommandError, CommandError(new_msg), sys.exc_info()[2])
             # Emit the post sync signal. This allows individual
             # applications to respond as if the database had been
             # sync'd from scratch.

django/core/serializers/json.py

@@ -8,6 +8,7 @@ from __future__ import absolute_import
 import datetime
 import decimal
 import json
+import sys
 
 from django.core.serializers.base import DeserializationError
 from django.core.serializers.python import Serializer as PythonSerializer
@@ -72,7 +73,7 @@ def Deserializer(stream_or_string, **options):
         raise
     except Exception as e:
         # Map to deserializer error
-        raise DeserializationError(e)
+        six.reraise(DeserializationError, DeserializationError(e), sys.exc_info()[2])
 
 
 class DjangoJSONEncoder(json.JSONEncoder):

django/core/serializers/pyyaml.py

@@ -6,6 +6,7 @@ Requires PyYaml (http://pyyaml.org/), but that's checked for in __init__.
 
 import decimal
 import yaml
+import sys
 from io import StringIO
 
 from django.db import models
@@ -71,4 +72,4 @@ def Deserializer(stream_or_string, **options):
         raise
     except Exception as e:
         # Map to deserializer error
-        raise DeserializationError(e)
+        six.reraise(DeserializationError, DeserializationError(e), sys.exc_info()[2])

django/core/servers/basehttp.py

@@ -24,6 +24,7 @@ from wsgiref.util import FileWrapper   # for backwards compatibility
 from django.core.management.color import color_style
 from django.core.wsgi import get_wsgi_application
 from django.utils.module_loading import import_by_path
+from django.utils import six
 
 __all__ = ['WSGIServer', 'WSGIRequestHandler']
 
@@ -121,7 +122,7 @@ class WSGIServer(simple_server.WSGIServer, object):
         try:
             super(WSGIServer, self).server_bind()
         except Exception as e:
-            raise WSGIServerException(e)
+            six.reraise(WSGIServerException, WSGIServerException(e), sys.exc_info()[2])
         self.setup_environ()
 
 

django/forms/fields.py

@@ -8,6 +8,7 @@ import copy
 import datetime
 import os
 import re
+import sys
 try:
     from urllib.parse import urlsplit, urlunsplit
 except ImportError:     # Python 2
@@ -619,7 +620,7 @@ class ImageField(FileField):
             # raised. Catch and re-raise.
             raise
         except Exception: # Python Imaging Library doesn't recognize it as an image
-            raise ValidationError(self.error_messages['invalid_image'])
+            six.reraise(ValidationError, ValidationError(self.error_messages['invalid_image']), sys.exc_info()[2])
         if hasattr(f, 'seek') and callable(f.seek):
             f.seek(0)
         return f

django/forms/util.py

@@ -6,6 +6,8 @@ from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils.safestring import mark_safe
 from django.utils import timezone
 from django.utils.translation import ugettext_lazy as _
+from django.utils import six
+import sys
 
 # Import ValidationError so that it can be imported from this
 # module to maintain backwards compatibility.
@@ -78,11 +80,12 @@ def from_current_timezone(value):
         try:
             return timezone.make_aware(value, current_timezone)
         except Exception:
-            raise ValidationError(_('%(datetime)s couldn\'t be interpreted '
-                                    'in time zone %(current_timezone)s; it '
-                                    'may be ambiguous or it may not exist.')
-                                  % {'datetime': value,
-                                     'current_timezone': current_timezone})
+            msg = _(
+                '%(datetime)s couldn\'t be interpreted '
+                'in time zone %(current_timezone)s; it '
+                'may be ambiguous or it may not exist.') % {'datetime': value, 'current_timezone':
+                current_timezone}
+            six.reraise(ValidationError, ValidationError(msg), sys.exc_info()[2])
     return value
 
 def to_current_timezone(value):

django/http/multipartparser.py

@@ -8,6 +8,7 @@ from __future__ import unicode_literals
 
 import base64
 import cgi
+import sys
 
 from django.conf import settings
 from django.core.exceptions import SuspiciousOperation
@@ -209,7 +210,8 @@ class MultiPartParser(object):
                                     chunk = base64.b64decode(chunk)
                                 except Exception as e:
                                     # Since this is only a chunk, any error is an unfixable error.
-                                    raise MultiPartParserError("Could not decode base64 data: %r" % e)
+                                    msg = "Could not decode base64 data: %r" % e
+                                    six.reraise(MultiPartParserError, MultiPartParserError(msg), sys.exc_info()[2])
 
                             for i, handler in enumerate(handlers):
                                 chunk_length = len(chunk)

django/templatetags/i18n.py

 from __future__ import unicode_literals
 import re
+import sys
 
 from django.conf import settings
 from django.template import (Node, Variable, TemplateSyntaxError,
@@ -424,8 +425,10 @@ def do_block_translate(parser, token):
                 value = remaining_bits.pop(0)
                 value = parser.compile_filter(value)
             except Exception:
-                raise TemplateSyntaxError('"context" in %r tag expected '
-                                          'exactly one argument.' % bits[0])
+                msg = (
+                    '"context" in %r tag expected '
+                    'exactly one argument.') % bits[0]
+                six.reraise(TemplateSyntaxError, TemplateSyntaxError(msg), sys.exc_info()[2])
         else:
             raise TemplateSyntaxError('Unknown argument for %r tag: %r.' %
                                       (bits[0], option))

django/test/testcases.py

@@ -1119,8 +1119,8 @@ class LiveServerTestCase(TransactionTestCase):
                     for port in range(extremes[0], extremes[1] + 1):
                         possible_ports.append(port)
         except Exception:
-            raise ImproperlyConfigured('Invalid address ("%s") for live '
-                'server.' % specified_address)
+            msg = 'Invalid address ("%s") for live server.' % specified_address
+            six.reraise(ImproperlyConfigured, ImproperlyConfigured(msg), sys.exc_info()[2])
         cls.server_thread = LiveServerThread(
             host, possible_ports, connections_override)
         cls.server_thread.daemon = True

django/utils/http.py

@@ -144,7 +144,7 @@ def parse_http_date(date):
         result = datetime.datetime(year, month, day, hour, min, sec)
         return calendar.timegm(result.utctimetuple())
     except Exception:
-        raise ValueError("%r is not a valid date" % date)
+        six.reraise(ValueError, ValueError("%r is not a valid date" % date), sys.exc_info()[2])
 
 def parse_http_date_safe(date):
     """