32 files changed, 156 insertions, 367 deletions

diff --git a/src/mailman/app/docs/bounces.rst b/src/mailman/app/docs/bounces.rst
index 127a05ef6..99eae8b2c 100644
--- a/src/mailman/app/docs/bounces.rst
+++ b/src/mailman/app/docs/bounces.rst
@@ -66,7 +66,7 @@ An error message can be given when the message is bounced, and this will be
 included in the payload of the text/plain part.  The error message must be
 passed in as an instance of a ``RejectMessage`` exception.
 
-    >>> from mailman.core.errors import RejectMessage
+    >>> from mailman.interfaces.pipeline import RejectMessage
     >>> error = RejectMessage("This wasn't very important after all.")
     >>> bounce_message(mlist, msg, error)
     >>> items = get_queue_messages('virgin')
diff --git a/src/mailman/chains/reject.py b/src/mailman/chains/reject.py
index 657e788af..f0926cd8c 100644
--- a/src/mailman/chains/reject.py
+++ b/src/mailman/chains/reject.py
@@ -22,9 +22,9 @@ import logging
 from mailman import public
 from mailman.app.bounces import bounce_message
 from mailman.chains.base import TerminalChainBase
-from mailman.core.errors import RejectMessage
 from mailman.core.i18n import _
 from mailman.interfaces.chain import RejectEvent
+from mailman.interfaces.pipeline import RejectMessage
 from zope.event import notify
 
 
diff --git a/src/mailman/core/api.py b/src/mailman/core/api.py
index 39c108db2..b7841a9d8 100644
--- a/src/mailman/core/api.py
+++ b/src/mailman/core/api.py
@@ -17,19 +17,15 @@
 
 """REST web service API contexts."""
 
-__all__ = [
-    'API30',
-    'API31',
-    ]
-
-
 from lazr.config import as_boolean
+from mailman import public
 from mailman.config import config
 from mailman.interfaces.api import IAPI
 from uuid import UUID
 from zope.interface import implementer
 
 
+@public
 @implementer(IAPI)
 class API30:
     version = '3.0'
@@ -58,6 +54,7 @@ class API30:
         return UUID(int=int(uuid))
 
 
+@public
 @implementer(IAPI)
 class API31:
     version = '3.1'
diff --git a/src/mailman/core/chains.py b/src/mailman/core/chains.py
index 6a98b2a33..3a503f193 100644
--- a/src/mailman/core/chains.py
+++ b/src/mailman/core/chains.py
@@ -17,12 +17,7 @@
 
 """Application support for chain processing."""
 
-__all__ = [
-    'initialize',
-    'process',
-    ]
-
-
+from mailman import public
 from mailman.chains.base import Chain, TerminalChainBase
 from mailman.config import config
 from mailman.interfaces.chain import LinkAction, IChain
@@ -30,6 +25,7 @@ from mailman.utilities.modules import find_components
 from zope.interface.verify import verifyObject
 
 
+@public
 def process(mlist, msg, msgdata, start_chain='default-posting-chain'):
     """Process the message through a chain.
 
@@ -85,13 +81,14 @@ def process(mlist, msg, msgdata, start_chain='default-posting-chain'):
                 link.function(mlist, msg, msgdata)
             else:
                 raise AssertionError(
-                    'Bad link action: {0}'.format(link.action))
+                    'Bad link action: {}'.format(link.action))
         else:
             # The rule did not match; keep going.
             if link.rule.record:
                 misses.append(link.rule.name)
 
 
+@public
 def initialize():
     """Set up chains, both built-in and from the database."""
     for chain_class in find_components('mailman.chains', IChain):
diff --git a/src/mailman/core/constants.py b/src/mailman/core/constants.py
index 3b6526f38..167ffef8b 100644
--- a/src/mailman/core/constants.py
+++ b/src/mailman/core/constants.py
@@ -17,11 +17,6 @@
 
 """Various constants and enumerations."""
 
-__all__ = [
-    'system_preferences',
-    ]
-
-
 from mailman.config import config
 from mailman.interfaces.languages import ILanguageManager
 from mailman.interfaces.member import DeliveryMode, DeliveryStatus
@@ -30,7 +25,6 @@ from zope.component import getUtility
 from zope.interface import implementer
 
 
-
 @implementer(IPreferences)
 class SystemDefaultPreferences:
     """The default system preferences."""
@@ -48,5 +42,5 @@ class SystemDefaultPreferences:
         return getUtility(ILanguageManager)[config.mailman.default_language]
 
 
-
 system_preferences = SystemDefaultPreferences()
+__all__ = ['system_preferences']
diff --git a/src/mailman/core/errors.py b/src/mailman/core/errors.py
deleted file mode 100644
index c293e81cb..000000000
--- a/src/mailman/core/errors.py
+++ /dev/null
@@ -1,110 +0,0 @@
-# Copyright (C) 1998-2016 by the Free Software Foundation, Inc.
-#
-# This file is part of GNU Mailman.
-#
-# GNU Mailman is free software: you can redistribute it and/or modify it under
-# the terms of the GNU General Public License as published by the Free
-# Software Foundation, either version 3 of the License, or (at your option)
-# any later version.
-#
-# GNU Mailman is distributed in the hope that it will be useful, but WITHOUT
-# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
-# more details.
-#
-# You should have received a copy of the GNU General Public License along with
-# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
-
-"""Legacy Mailman exceptions.
-
-This module is largely obsolete, though not all exceptions in use have been
-migrated to their proper location.  There are still a number of Mailman 2.1
-exceptions floating about in here too.
-
-The right place for exceptions is in the interface module for their related
-interfaces.
-"""
-
-
-__all__ = [
-    'DiscardMessage',
-    'HandlerError',
-    'HoldMessage',
-    'LostHeldMessage',
-    'RESTError',
-    'ReadOnlyPATCHRequestError',
-    'RejectMessage',
-    'UnknownPATCHRequestError',
-    ]
-
-
-
-class MailmanError(Exception):
-    """Base class for all Mailman errors."""
-    pass
-
-
-
-# Exceptions for admin request database
-class LostHeldMessage(MailmanError):
-    """Held message was lost."""
-    pass
-
-
-
-def _(s):
-    return s
-
-
-# Exceptions for the Handler subsystem
-class HandlerError(MailmanError):
-    """Base class for all handler errors."""
-
-    def __init__(self, message=None):
-        self.message = message
-
-    def __str__(self):
-        return self.message
-
-
-class HoldMessage(HandlerError):
-    """Base class for all message-being-held short circuits."""
-
-    # funky spelling is necessary to break import loops
-    reason = _('For some unknown reason')
-
-    def reason_notice(self):
-        return self.reason
-
-    # funky spelling is necessary to break import loops
-    rejection = _('Your message was rejected')
-
-    def rejection_notice(self, mlist):
-        return self.rejection
-
-
-class DiscardMessage(HandlerError):
-    """The message can be discarded with no further action"""
-
-
-class RejectMessage(HandlerError):
-    """The message will be bounced back to the sender"""
-
-
-
-class RESTError(MailmanError):
-    """Base class for REST API errors."""
-
-
-class UnknownPATCHRequestError(RESTError):
-    """A PATCH request contained an unknown attribute."""
-
-    def __init__(self, attribute):
-        self.attribute = attribute
-
-
-class ReadOnlyPATCHRequestError(RESTError):
-    """A PATCH request contained a read-only attribute."""
-
-    def __init__(self, attribute):
-        self.attribute = attribute
diff --git a/src/mailman/core/i18n.py b/src/mailman/core/i18n.py
index 28a231a97..ebe61894a 100644
--- a/src/mailman/core/i18n.py
+++ b/src/mailman/core/i18n.py
@@ -17,24 +17,23 @@
 
 """Internationalization."""
 
-__all__ = [
-    '_',
-    'ctime',
-    'initialize',
-    ]
-
-
-import time
 import mailman.messages
 
 from flufl.i18n import PackageStrategy, registry
 from mailman.interfaces.configuration import ConfigurationUpdatedEvent
 
 
+# We can't use @mailman.public here because of circular imports.
+__all__ = [
+    '_',
+    'handle_ConfigurationUpdatedEvent',
+    'initialize',
+    ]
+
+
 _ = None
 
 
-
 def initialize(application=None):
     """Initialize the i18n subsystem.
 
@@ -50,70 +49,6 @@ def initialize(application=None):
     _ = application._
 
 
-
-def ctime(date):
-    """Translate a ctime.
-
-    :param date: The date to translate.
-    :type date: str or time float
-    :return: The translated date.
-    :rtype: string
-    """
-    # Don't make these module globals since we have to do runtime translation
-    # of the strings anyway.
-    daysofweek = [
-        _('Mon'), _('Tue'), _('Wed'), _('Thu'),
-        _('Fri'), _('Sat'), _('Sun')
-        ]
-    months = [
-        '',
-        _('Jan'), _('Feb'), _('Mar'), _('Apr'), _('May'), _('Jun'),
-        _('Jul'), _('Aug'), _('Sep'), _('Oct'), _('Nov'), _('Dec')
-        ]
-
-    tzname = _('Server Local Time')
-    if isinstance(date, str):
-        try:
-            year, mon, day, hh, mm, ss, wday, ydat, dst = time.strptime(date)
-            if dst in (0, 1):
-                tzname = time.tzname[dst]
-            else:
-                # MAS: No exception but dst = -1 so try
-                return ctime(time.mktime((year, mon, day, hh, mm, ss, wday,
-                                          ydat, dst)))
-        except (ValueError, AttributeError):
-            try:
-                wday, mon, day, hms, year = date.split()
-                hh, mm, ss = hms.split(':')
-                year = int(year)
-                day = int(day)
-                hh = int(hh)
-                mm = int(mm)
-                ss = int(ss)
-            except ValueError:
-                return date
-            else:
-                for i in range(0, 7):
-                    wconst = (1999, 1, 1, 0, 0, 0, i, 1, 0)
-                    if wday.lower() == time.strftime('%a', wconst).lower():
-                        wday = i
-                        break
-                for i in range(1, 13):
-                    mconst = (1999, i, 1, 0, 0, 0, 0, 1, 0)
-                    if mon.lower() == time.strftime('%b', mconst).lower():
-                        mon = i
-                        break
-    else:
-        year, mon, day, hh, mm, ss, wday, yday, dst = time.localtime(date)
-        if dst in (0, 1):
-            tzname = time.tzname[dst]
-
-    wday = daysofweek[wday]
-    mon = months[mon]
-    return _('$wday $mon $day $hh:$mm:$ss $tzname $year')
-
-
-
 def handle_ConfigurationUpdatedEvent(event):
     if isinstance(event, ConfigurationUpdatedEvent):
         _.default = event.config.mailman.default_language
diff --git a/src/mailman/core/initialize.py b/src/mailman/core/initialize.py
index bc6da9639..3c724aecd 100644
--- a/src/mailman/core/initialize.py
+++ b/src/mailman/core/initialize.py
@@ -24,20 +24,12 @@ line argument parsing, since some of the initialization behavior is controlled
 by the command line arguments.
 """
 
-__all__ = [
-    'initialize',
-    'initialize_1',
-    'initialize_2',
-    'initialize_3',
-    'INHIBIT_CONFIG_FILE',
-    ]
-
-
 import os
 import sys
 import mailman.config.config
 import mailman.core.logging
 
+from mailman import public
 from mailman.interfaces.database import IDatabaseFactory
 from mailman.utilities.modules import call_name
 from pkg_resources import resource_string as resource_bytes
@@ -49,9 +41,9 @@ from zope.configuration import xmlconfig
 # existing configuration file.  Otherwise the existence of say a
 # ~/.mailman.cfg file can break tests.
 INHIBIT_CONFIG_FILE = object()
+__all__ = ['INHIBIT_CONFIG_FILE']
 
 
-
 def search_for_configuration_file():
     """Search the file system for a configuration file to use.
 
@@ -89,12 +81,12 @@ def search_for_configuration_file():
     return None
 
 
-
 # These initialization calls are separated for the testing framework, which
 # needs to do some internal calculations after config file loading and log
 # initialization, but before database initialization.  Generally all other
 # code will just call initialize().
 
+@public
 def initialize_1(config_path=None):
     """First initialization step.
 
@@ -135,6 +127,7 @@ def initialize_1(config_path=None):
         mailman.config.config.push('extra testing config', extra_cfg)
 
 
+@public
 def initialize_2(debug=False, propagate_logs=None, testing=False):
     """Second initialization step.
 
@@ -174,6 +167,7 @@ def initialize_2(debug=False, propagate_logs=None, testing=False):
     initialize_commands()
 
 
+@public
 def initialize_3():
     """Third initialization step.
 
@@ -185,7 +179,7 @@ def initialize_3():
         call_name(config.mailman.post_hook)
 
 
-
+@public
 def initialize(config_path=None, propagate_logs=None):
     initialize_1(config_path)
     initialize_2(propagate_logs=propagate_logs)
diff --git a/src/mailman/core/logging.py b/src/mailman/core/logging.py
index 24aaa0ffa..298923d3f 100644
--- a/src/mailman/core/logging.py
+++ b/src/mailman/core/logging.py
@@ -17,25 +17,19 @@
 
 """Logging initialization, using Python's standard logging package."""
 
-__all__ = [
-    'initialize',
-    'reopen',
-    ]
-
-
 import os
 import sys
 import codecs
 import logging
 
 from lazr.config import as_boolean, as_log_level
+from mailman import public
 from mailman.config import config
 
 
 _handlers = {}
 
 
-
 # XXX I would love to simplify things and use Python's WatchedFileHandler, but
 # there are two problems.  First, it's more difficult to handle the test
 # suite's need to reopen the file handler to a different path.
@@ -50,7 +44,7 @@ class ReopenableFileHandler(logging.Handler):
     """A file handler that supports reopening."""
 
     def __init__(self, name, filename):
-        logging.Handler.__init__(self)
+        super().__init__()
         self.name = name
         self.filename = filename
         self._stream = self._open()
@@ -70,9 +64,9 @@ class ReopenableFileHandler(logging.Handler):
         try:
             msg = self.format(record)
             try:
-                stream.write('{0}'.format(msg))
+                stream.write('{}'.format(msg))
             except UnicodeError:
-                stream.write('{0}'.format(msg.encode('string-escape')))
+                stream.write('{}'.format(msg.encode('string-escape')))
             if msg[-1] != '\n':
                 stream.write('\n')
             self.flush()
@@ -83,7 +77,7 @@ class ReopenableFileHandler(logging.Handler):
         self.flush()
         self._stream.close()
         self._stream = None
-        logging.Handler.close(self)
+        super().close()
 
     def reopen(self, filename=None):
         """Reopen the output stream.
@@ -98,7 +92,6 @@ class ReopenableFileHandler(logging.Handler):
         self._stream = self._open()
 
 
-
 def _init_logger(propagate, sub_name, log, logger_config):
     # Get settings from log configuration file (or defaults).
     log_format = logger_config.format
@@ -120,6 +113,7 @@ def _init_logger(propagate, sub_name, log, logger_config):
     log.addHandler(handler)
 
 
+@public
 def initialize(propagate=None):
     """Initialize all logs.
 
@@ -158,14 +152,15 @@ def initialize(propagate=None):
             log = logging.getLogger(logger_name)
         _init_logger(propagate, sub_name, log, logger_config)
 
-
+
+@public
 def reopen():
     """Re-open all log files."""
     for handler in _handlers.values():
         handler.reopen()
 
 
-
+@public
 def get_handler(sub_name):
     """Return the handler associated with a named logger.
 
diff --git a/src/mailman/core/pipelines.py b/src/mailman/core/pipelines.py
index a353e3ad8..5df21ed15 100644
--- a/src/mailman/core/pipelines.py
+++ b/src/mailman/core/pipelines.py
@@ -17,24 +17,15 @@
 
 """Built-in pipelines."""
 
-__all__ = [
-    'BasePipeline',
-    'OwnerPipeline',
-    'PostingPipeline',
-    'VirginPipeline',
-    'initialize',
-    'process',
-    ]
-
-
 import logging
 
+from mailman import public
 from mailman.app.bounces import bounce_message
 from mailman.config import config
-from mailman.core import errors
 from mailman.core.i18n import _
 from mailman.interfaces.handler import IHandler
-from mailman.interfaces.pipeline import IPipeline
+from mailman.interfaces.pipeline import (
+    DiscardMessage, IPipeline, RejectMessage)
 from mailman.utilities.modules import find_components
 from zope.interface import implementer
 from zope.interface.verify import verifyObject
@@ -44,7 +35,7 @@ dlog = logging.getLogger('mailman.debug')
 vlog = logging.getLogger('mailman.vette')
 
 
-
+@public
 def process(mlist, msg, msgdata, pipeline_name='built-in'):
     """Process the message through the given pipeline.
 
@@ -56,22 +47,22 @@ def process(mlist, msg, msgdata, pipeline_name='built-in'):
     message_id = msg.get('message-id', 'n/a')
     pipeline = config.pipelines[pipeline_name]
     for handler in pipeline:
-        dlog.debug('{0} pipeline {1} processing: {2}'.format(
+        dlog.debug('{} pipeline {} processing: {}'.format(
             message_id, pipeline_name, handler.name))
         try:
             handler.process(mlist, msg, msgdata)
-        except errors.DiscardMessage as error:
+        except DiscardMessage as error:
             vlog.info(
-                '{0} discarded by "{1}" pipeline handler "{2}": {3}'.format(
+                '{} discarded by "{}" pipeline handler "{}": {}'.format(
                     message_id, pipeline_name, handler.name, error.message))
-        except errors.RejectMessage as error:
+        except RejectMessage as error:
             vlog.info(
-                '{0} rejected by "{1}" pipeline handler "{2}": {3}'.format(
+                '{} rejected by "{}" pipeline handler "{}": {}'.format(
                     message_id, pipeline_name, handler.name, error.message))
             bounce_message(mlist, msg, error)
 
 
-
+@public
 @implementer(IPipeline)
 class BasePipeline:
     """Base pipeline implementation."""
@@ -88,7 +79,7 @@ class BasePipeline:
         yield from self._handlers
 
 
-
+@public
 class OwnerPipeline(BasePipeline):
     """The built-in owner pipeline."""
 
@@ -101,6 +92,7 @@ class OwnerPipeline(BasePipeline):
         )
 
 
+@public
 class PostingPipeline(BasePipeline):
     """The built-in posting pipeline."""
 
@@ -127,6 +119,7 @@ class PostingPipeline(BasePipeline):
         )
 
 
+@public
 class VirginPipeline(BasePipeline):
     """The processing pipeline for virgin messages.
 
@@ -141,7 +134,7 @@ class VirginPipeline(BasePipeline):
         )
 
 
-
+@public
 def initialize():
     """Initialize the pipelines."""
     # Find all handlers in the registered plugins.
@@ -149,7 +142,7 @@ def initialize():
         handler = handler_class()
         verifyObject(IHandler, handler)
         assert handler.name not in config.handlers, (
-            'Duplicate handler "{0}" found in {1}'.format(
+            'Duplicate handler "{}" found in {}'.format(
                 handler.name, handler_class))
         config.handlers[handler.name] = handler
     # Set up some pipelines.
diff --git a/src/mailman/core/rules.py b/src/mailman/core/rules.py
index b593214f8..f6ca87726 100644
--- a/src/mailman/core/rules.py
+++ b/src/mailman/core/rules.py
@@ -17,17 +17,14 @@
 
 """Various rule helpers"""
 
-__all__ = [
-    'initialize',
-    ]
-
-
+from mailman import public
 from mailman.config import config
 from mailman.interfaces.rules import IRule
 from mailman.utilities.modules import find_components
 from zope.interface.verify import verifyObject
 
 
+@public
 def initialize():
     """Find and register all rules in all plugins."""
     # Find rules in plugins.
diff --git a/src/mailman/core/runner.py b/src/mailman/core/runner.py
index 64b830131..4c9c59464 100644
--- a/src/mailman/core/runner.py
+++ b/src/mailman/core/runner.py
@@ -17,11 +17,6 @@
 
 """The process runner base class."""
 
-__all__ = [
-    'Runner',
-    ]
-
-
 import time
 import signal
 import logging
@@ -29,6 +24,7 @@ import traceback
 
 from io import StringIO
 from lazr.config import as_boolean, as_timedelta
+from mailman import public
 from mailman.config import config
 from mailman.core.i18n import _
 from mailman.core.logging import reopen
@@ -47,7 +43,7 @@ elog = logging.getLogger('mailman.error')
 rlog = logging.getLogger('mailman.runner')
 
 
-
+@public
 @implementer(IRunner)
 class Runner:
     is_queue_runner = True
@@ -74,7 +70,7 @@ class Runner:
                 name, self.queue_directory, slice, numslices, True)
         else:
             self.queue_directory = None
-            self.switchboard= None
+            self.switchboard = None
         self.sleep_time = as_timedelta(section.sleep_time)
         # sleep_time is a timedelta; turn it into a float for time.sleep().
         self.sleep_float = (86400 * self.sleep_time.days +
@@ -86,7 +82,7 @@ class Runner:
         self.status = 0
 
     def __repr__(self):
-        return '<{0} at {1:#x}>'.format(self.__class__.__name__, id(self))
+        return '<{} at {:#x}>'.format(self.__class__.__name__, id(self))
 
     def signal_handler(self, signum, frame):
         signame = {
diff --git a/src/mailman/core/switchboard.py b/src/mailman/core/switchboard.py
index ae85bf22e..122d6b85d 100644
--- a/src/mailman/core/switchboard.py
+++ b/src/mailman/core/switchboard.py
@@ -24,12 +24,6 @@ written.  First, the message is written to the pickle, then the metadata
 dictionary is written.
 """
 
-__all__ = [
-    'Switchboard',
-    'handle_ConfigurationUpdatedEvent',
-    ]
-
-
 import os
 import time
 import email
@@ -37,6 +31,7 @@ import pickle
 import hashlib
 import logging
 
+from mailman import public
 from mailman.config import config
 from mailman.email.message import Message
 from mailman.interfaces.configuration import ConfigurationUpdatedEvent
@@ -60,7 +55,7 @@ MAX_BAK_COUNT = 3
 elog = logging.getLogger('mailman.error')
 
 
-
+@public
 @implementer(ISwitchboard)
 class Switchboard:
     """See `ISwitchboard`."""
@@ -83,7 +78,7 @@ class Switchboard:
         :type recover: bool
         """
         assert (numslices & (numslices - 1)) == 0, (
-            'Not a power of 2: {0}'.format(numslices))
+            'Not a power of 2: {}'.format(numslices))
         self.name = name
         self.queue_directory = queue_directory
         # If configured to, create the directory if it doesn't yet exist.
@@ -253,7 +248,7 @@ class Switchboard:
                         os.rename(src, dst)
 
 
-
+@public
 def handle_ConfigurationUpdatedEvent(event):
     """Initialize the global switchboards for input/output."""
     if not isinstance(event, ConfigurationUpdatedEvent):
diff --git a/src/mailman/core/system.py b/src/mailman/core/system.py
index f773a9f7f..c4489d926 100644
--- a/src/mailman/core/system.py
+++ b/src/mailman/core/system.py
@@ -17,11 +17,6 @@
 
 """System information."""
 
-__all__ = [
-    'system',
-    ]
-
-
 import sys
 
 from mailman import version
@@ -29,7 +24,6 @@ from mailman.interfaces.system import ISystem
 from zope.interface import implementer
 
 
-
 @implementer(ISystem)
 class System:
     """See `ISystem`."""
@@ -46,3 +40,4 @@ class System:
 
 
 system = System()
+__all__ = ['system']
diff --git a/src/mailman/core/tests/test_pipelines.py b/src/mailman/core/tests/test_pipelines.py
index f36679347..98ce125a7 100644
--- a/src/mailman/core/tests/test_pipelines.py
+++ b/src/mailman/core/tests/test_pipelines.py
@@ -17,31 +17,25 @@
 
 """Test the core modification pipelines."""
 
-__all__ = [
-    'TestOwnerPipeline',
-    'TestPostingPipeline',
-    ]
-
-
 import unittest
 
 from mailman.app.lifecycle import create_list
 from mailman.config import config
-from mailman.core.errors import DiscardMessage, RejectMessage
 from mailman.core.pipelines import process
 from mailman.interfaces.handler import IHandler
 from mailman.interfaces.member import MemberRole
-from mailman.interfaces.pipeline import IPipeline
+from mailman.interfaces.pipeline import (
+    DiscardMessage, IPipeline, RejectMessage)
 from mailman.interfaces.usermanager import IUserManager
 from mailman.testing.helpers import (
-    LogFileMark, digest_mbox, get_queue_messages, reset_the_world,
+    LogFileMark, digest_mbox, get_queue_messages,
     specialized_message_from_string as mfs)
 from mailman.testing.layers import ConfigLayer
+from operator import delitem
 from zope.component import getUtility
 from zope.interface import implementer
 
 
-
 @implementer(IHandler)
 class DiscardingHandler:
     name = 'discarding'
@@ -76,7 +70,6 @@ class RejectingPipeline:
         yield RejectHandler()
 
 
-
 class TestPostingPipeline(unittest.TestCase):
     """Test various aspects of the built-in postings pipeline."""
 
@@ -85,7 +78,9 @@ class TestPostingPipeline(unittest.TestCase):
     def setUp(self):
         self._mlist = create_list('test@example.com')
         config.pipelines['test-discarding'] = DiscardingPipeline()
+        self.addCleanup(delitem, config.pipelines, 'test-discarding')
         config.pipelines['test-rejecting'] = RejectingPipeline()
+        self.addCleanup(delitem, config.pipelines, 'test-rejecting')
         self._msg = mfs("""\
 From: Anne Person <anne@example.org>
 To: test@example.com
@@ -95,11 +90,6 @@ Message-ID: <ant>
 testing
 """)
 
-    def tearDown(self):
-        reset_the_world()
-        del config.pipelines['test-discarding']
-        del config.pipelines['test-rejecting']
-
     def test_rfc2369_headers(self):
         # Ensure that RFC 2369 List-* headers are added.
         msgdata = {}
@@ -129,9 +119,8 @@ testing
             '"rejecting": by test handler'))
         # In the rejection case, the original message will also be in the
         # virgin queue.
-        messages = get_queue_messages('virgin')
-        self.assertEqual(len(messages), 1)
-        self.assertEqual(str(messages[0].msg['subject']), 'a test')
+        items = get_queue_messages('virgin', expected_count=1)
+        self.assertEqual(str(items[0].msg['subject']), 'a test')
 
     def test_decorate_bulk(self):
         # Ensure that bulk postings get decorated with the footer.
@@ -160,18 +149,14 @@ testing
         process(self._mlist, self._msg, {},
                 pipeline_name='default-posting-pipeline')
         for queue in ('archive', 'nntp'):
-            messages = get_queue_messages(queue)
-            self.assertEqual(
-                len(messages), 1,
-                'Queue {} has {} messages'.format(queue, len(messages)))
-            payload = messages[0].msg.get_payload()
+            items = get_queue_messages(queue, expected_count=1)
+            payload = items[0].msg.get_payload()
             self.assertNotIn('Test mailing list', payload)
         self.assertEqual(len(digest_mbox(self._mlist)), 1)
         payload = digest_mbox(self._mlist)[0].get_payload()
         self.assertNotIn('Test mailing list', payload)
 
 
-
 class TestOwnerPipeline(unittest.TestCase):
     """Test various aspects of the built-in owner pipeline."""
 
@@ -204,7 +189,6 @@ To: test-owner@example.com
         # outgoing queue.
         process(self._mlist, self._msg, {},
                 pipeline_name='default-owner-pipeline')
-        messages = get_queue_messages('out', sort_on='to')
-        self.assertEqual(len(messages), 1)
-        self.assertEqual(messages[0].msgdata['recipients'],
+        items = get_queue_messages('out', sort_on='to', expected_count=1)
+        self.assertEqual(items[0].msgdata['recipients'],
                          set(('anne@example.com', 'bart@example.com')))
diff --git a/src/mailman/core/tests/test_runner.py b/src/mailman/core/tests/test_runner.py
index e06357d7c..69911f95e 100644
--- a/src/mailman/core/tests/test_runner.py
+++ b/src/mailman/core/tests/test_runner.py
@@ -17,11 +17,6 @@
 
 """Test some Runner base class behavior."""
 
-__all__ = [
-    'TestRunner',
-    ]
-
-
 import unittest
 
 from mailman.app.lifecycle import create_list
@@ -38,13 +33,11 @@ from mailman.testing.helpers import (
 from mailman.testing.layers import ConfigLayer
 
 
-
 class CrashingRunner(Runner):
     def _dispose(self, mlist, msg, msgdata):
         raise RuntimeError('borked')
 
 
-
 class TestRunner(unittest.TestCase):
     """Test the Runner base class behavior."""
 
@@ -77,17 +70,16 @@ Message-ID: <ant>
         # message, and metadata.
         self.assertEqual(len(self._events), 1)
         event = self._events[0]
-        self.assertTrue(isinstance(event, RunnerCrashEvent))
+        self.assertIsInstance(event, RunnerCrashEvent)
         self.assertEqual(event.mailing_list, self._mlist)
         self.assertEqual(event.message['message-id'], '<ant>')
         self.assertEqual(event.metadata['listid'], 'test.example.com')
-        self.assertTrue(isinstance(event.error, RuntimeError))
+        self.assertIsInstance(event.error, RuntimeError)
         self.assertEqual(str(event.error), 'borked')
-        self.assertTrue(isinstance(event.runner, CrashingRunner))
+        self.assertIsInstance(event.runner, CrashingRunner)
         # The message should also have ended up in the shunt queue.
-        shunted = get_queue_messages('shunt')
-        self.assertEqual(len(shunted), 1)
-        self.assertEqual(shunted[0].msg['message-id'], '<ant>')
+        items = get_queue_messages('shunt', expected_count=1)
+        self.assertEqual(items[0].msg['message-id'], '<ant>')
 
     def test_digest_messages(self):
         # In LP: #1130697, the digest runner creates MIME digests using the
@@ -112,18 +104,17 @@ Message-ID: <ant>
         runner.run()
         error_text = error_log.read()
         self.assertEqual(len(error_text), 0, error_text)
-        self.assertEqual(len(get_queue_messages('shunt')), 0)
-        messages = get_queue_messages('out')
-        self.assertEqual(len(messages), 2)
+        get_queue_messages('shunt', expected_count=0)
+        items = get_queue_messages('out', expected_count=2)
         # Which one is the MIME digest?
         mime_digest = None
-        for bag in messages:
-            if bag.msg.get_content_type() == 'multipart/mixed':
+        for item in items:
+            if item.msg.get_content_type() == 'multipart/mixed':
                 assert mime_digest is None, 'Found two MIME digests'
-                mime_digest = bag.msg
+                mime_digest = item.msg
         # The cook-headers handler ran.
         self.assertIn('x-mailman-version', mime_digest)
         self.assertEqual(mime_digest['precedence'], 'list')
         # The list's -request address is the original sender.
-        self.assertEqual(bag.msgdata['original_sender'],
+        self.assertEqual(item.msgdata['original_sender'],
                          'test-request@example.com')
diff --git a/src/mailman/core/tests/test_switchboard.py b/src/mailman/core/tests/test_switchboard.py
index b2e10fc3f..9389959b0 100644
--- a/src/mailman/core/tests/test_switchboard.py
+++ b/src/mailman/core/tests/test_switchboard.py
@@ -17,11 +17,6 @@
 
 """Switchboard tests."""
 
-__all__ = [
-    'TestSwitchboard',
-    ]
-
-
 import unittest
 
 from mailman.config import config
diff --git a/src/mailman/handlers/member_recipients.py b/src/mailman/handlers/member_recipients.py
index f224b4f36..6a28af11a 100644
--- a/src/mailman/handlers/member_recipients.py
+++ b/src/mailman/handlers/member_recipients.py
@@ -29,10 +29,10 @@ __all__ = [
 
 
 from mailman.config import config
-from mailman.core import errors
 from mailman.core.i18n import _
 from mailman.interfaces.handler import IHandler
 from mailman.interfaces.member import DeliveryStatus
+from mailman.interfaces.pipeline import RejectMessage
 from mailman.utilities.string import wrap
 from zope.interface import implementer
 
@@ -82,7 +82,7 @@ class MemberRecipients:
 Your urgent message to the $mlist.display_name mailing list was not authorized
 for delivery.  The original message as received by Mailman is attached.
 """)
-                raise errors.RejectMessage(wrap(text))
+                raise RejectMessage(wrap(text))
         # Calculate the regular recipients of the message
         recipients = set(member.address.email
                          for member in mlist.regular_members.members
diff --git a/src/mailman/handlers/mime_delete.py b/src/mailman/handlers/mime_delete.py
index 38495ebc9..a1e861bf8 100644
--- a/src/mailman/handlers/mime_delete.py
+++ b/src/mailman/handlers/mime_delete.py
@@ -42,11 +42,11 @@ from email.mime.text import MIMEText
 from itertools import count
 from lazr.config import as_boolean
 from mailman.config import config
-from mailman.core import errors
 from mailman.core.i18n import _
 from mailman.email.message import OwnerNotification
 from mailman.interfaces.action import FilterAction
 from mailman.interfaces.handler import IHandler
+from mailman.interfaces.pipeline import DiscardMessage, RejectMessage
 from mailman.utilities.string import oneline
 from mailman.version import VERSION
 from string import Template
@@ -60,7 +60,7 @@ log = logging.getLogger('mailman.error')
 def dispose(mlist, msg, msgdata, why):
     if mlist.filter_action is FilterAction.reject:
         # Bounce the message to the original author.
-        raise errors.RejectMessage(why)
+        raise RejectMessage(why)
     elif mlist.filter_action is FilterAction.forward:
         # Forward it on to the list moderators.
         text=_("""\
@@ -90,7 +90,7 @@ message.
             '{1} invalid FilterAction: {0}.  Treating as discard'.format(
                 mlist.fqdn_listname, mlist.filter_action.name))
     # Most cases also discard the message
-    raise errors.DiscardMessage(why)
+    raise DiscardMessage(why)
 
 
 
diff --git a/src/mailman/handlers/tests/test_filter.py b/src/mailman/handlers/tests/test_filter.py
index 141bd6c8d..0933d8b00 100644
--- a/src/mailman/handlers/tests/test_filter.py
+++ b/src/mailman/handlers/tests/test_filter.py
@@ -26,8 +26,8 @@ import unittest
 
 from mailman.app.lifecycle import create_list
 from mailman.config import config
-from mailman.core.errors import DiscardMessage
 from mailman.interfaces.mime import FilterAction
+from mailman.interfaces.pipeline import DiscardMessage
 from mailman.testing.helpers import specialized_message_from_string as mfs
 from mailman.testing.layers import ConfigLayer
 
diff --git a/src/mailman/handlers/tests/test_mimedel.py b/src/mailman/handlers/tests/test_mimedel.py
index d8829d995..d5670f1bc 100644
--- a/src/mailman/handlers/tests/test_mimedel.py
+++ b/src/mailman/handlers/tests/test_mimedel.py
@@ -33,10 +33,10 @@ import unittest
 from contextlib import ExitStack, contextmanager
 from mailman.app.lifecycle import create_list
 from mailman.config import config
-from mailman.core import errors
 from mailman.handlers import mime_delete
 from mailman.interfaces.action import FilterAction
 from mailman.interfaces.member import MemberRole
+from mailman.interfaces.pipeline import DiscardMessage, RejectMessage
 from mailman.interfaces.usermanager import IUserManager
 from mailman.testing.helpers import (
     LogFileMark, configuration, get_queue_messages,
@@ -90,7 +90,7 @@ Message-ID: <ant>
 
     def test_dispose_discard(self):
         self._mlist.filter_action = FilterAction.discard
-        with self.assertRaises(errors.DiscardMessage) as cm:
+        with self.assertRaises(DiscardMessage) as cm:
             mime_delete.dispose(self._mlist, self._msg, {}, 'discarding')
         self.assertEqual(cm.exception.message, 'discarding')
         # There should be no messages in the 'bad' queue.
@@ -98,7 +98,7 @@ Message-ID: <ant>
 
     def test_dispose_bounce(self):
         self._mlist.filter_action = FilterAction.reject
-        with self.assertRaises(errors.RejectMessage) as cm:
+        with self.assertRaises(RejectMessage) as cm:
             mime_delete.dispose(self._mlist, self._msg, {}, 'rejecting')
         self.assertEqual(cm.exception.message, 'rejecting')
         # There should be no messages in the 'bad' queue.
@@ -114,7 +114,7 @@ Message-ID: <ant>
         self._mlist.subscribe(bart, MemberRole.moderator)
         # Now set the filter action and dispose the message.
         self._mlist.filter_action = FilterAction.forward
-        with self.assertRaises(errors.DiscardMessage) as cm:
+        with self.assertRaises(DiscardMessage) as cm:
             mime_delete.dispose(self._mlist, self._msg, {}, 'forwarding')
         self.assertEqual(cm.exception.message, 'forwarding')
         # There should now be a multipart message in the virgin queue destined
@@ -156,7 +156,7 @@ message.
         # the site owner has indicated that filtered messages cannot be
         # preserved, then this is the same as discarding them.
         self._mlist.filter_action = FilterAction.preserve
-        with self.assertRaises(errors.DiscardMessage) as cm:
+        with self.assertRaises(DiscardMessage) as cm:
             mime_delete.dispose(self._mlist, self._msg, {}, 'not preserved')
         self.assertEqual(cm.exception.message, 'not preserved')
         # There should be no messages in the 'bad' queue.
@@ -169,7 +169,7 @@ message.
         # preserved, then this is similar to discarding the message except
         # that a copy is preserved in the 'bad' queue.
         self._mlist.filter_action = FilterAction.preserve
-        with self.assertRaises(errors.DiscardMessage) as cm:
+        with self.assertRaises(DiscardMessage) as cm:
             mime_delete.dispose(self._mlist, self._msg, {}, 'preserved')
         self.assertEqual(cm.exception.message, 'preserved')
         # There should be no messages in the 'bad' queue.
@@ -189,7 +189,7 @@ message.
                        FilterAction.defer):
             self._mlist.filter_action = action
             mark = LogFileMark('mailman.error')
-            with self.assertRaises(errors.DiscardMessage) as cm:
+            with self.assertRaises(DiscardMessage) as cm:
                 mime_delete.dispose(self._mlist, self._msg, {}, 'bad action')
             self.assertEqual(cm.exception.message, 'bad action')
             line = mark.readline()[:-1]
diff --git a/src/mailman/interfaces/configuration.py b/src/mailman/interfaces/configuration.py
index ba244d876..f68ba4785 100644
--- a/src/mailman/interfaces/configuration.py
+++ b/src/mailman/interfaces/configuration.py
@@ -24,7 +24,7 @@ __all__ = [
     ]
 
 
-from mailman.core.errors import MailmanError
+from mailman.interfaces.errors import MailmanError
 from zope.interface import Interface
 
 
diff --git a/src/mailman/interfaces/domain.py b/src/mailman/interfaces/domain.py
index 25aa54cc3..e978479df 100644
--- a/src/mailman/interfaces/domain.py
+++ b/src/mailman/interfaces/domain.py
@@ -28,7 +28,7 @@ __all__ = [
     ]
 
 
-from mailman.core.errors import MailmanError
+from mailman.interfaces.errors import MailmanError
 from zope.interface import Interface, Attribute
 
 
diff --git a/src/mailman/interfaces/errors.py b/src/mailman/interfaces/errors.py
index 64194a70d..6045e4868 100644
--- a/src/mailman/interfaces/errors.py
+++ b/src/mailman/interfaces/errors.py
@@ -22,11 +22,11 @@ components.  More specific exceptions will be located in the relevant
 interfaces.
 """
 
+# We can't use @mailman.public here because of circular imports.
 __all__ = [
     'MailmanError',
     ]
 
 
-
 class MailmanError(Exception):
     """Base class for all Mailman exceptions."""
diff --git a/src/mailman/interfaces/member.py b/src/mailman/interfaces/member.py
index f084391e2..91c2aab0a 100644
--- a/src/mailman/interfaces/member.py
+++ b/src/mailman/interfaces/member.py
@@ -34,7 +34,7 @@ __all__ = [
 
 
 from enum import Enum
-from mailman.core.errors import MailmanError
+from mailman.interfaces.errors import MailmanError
 from zope.interface import Interface, Attribute
 
 
diff --git a/src/mailman/interfaces/mta.py b/src/mailman/interfaces/mta.py
index 5cf9c79c4..8c168c3a1 100644
--- a/src/mailman/interfaces/mta.py
+++ b/src/mailman/interfaces/mta.py
@@ -24,7 +24,7 @@ __all__ = [
     ]
 
 
-from mailman.core.errors import MailmanError
+from mailman.interfaces.errors import MailmanError
 from zope.interface import Interface
 
 
diff --git a/src/mailman/interfaces/pipeline.py b/src/mailman/interfaces/pipeline.py
index b8830b003..5e39c2a3e 100644
--- a/src/mailman/interfaces/pipeline.py
+++ b/src/mailman/interfaces/pipeline.py
@@ -17,15 +17,41 @@
 
 """Interface for describing pipelines."""
 
-__all__ = [
-    'IPipeline',
-    ]
+from mailman import public
+from zope.interface import Interface, Attribute
 
 
-from zope.interface import Interface, Attribute
+# For i18n extraction.
+def _(s):
+    return s
+
+
+# These are thrown but they aren't exceptions so don't inherit from
+# mailman.interfaces.errors.MailmanError.  Python requires that they inherit
+# from BaseException.
+@public
+class DiscardMessage(BaseException):
+    """The message can be discarded with no further action"""
+
+    def __init__(self, message=None):
+        self.message = message
+
+    def __str__(self):
+        return self.message
+
+
+@public
+class RejectMessage(BaseException):
+    """The message will be bounced back to the sender"""
+
+    def __init__(self, message=None):
+        self.message = message
+
+    def __str__(self):
+        return self.message
 
 
-
+@public
 class IPipeline(Interface):
     """A pipeline of handlers."""
 
diff --git a/src/mailman/rest/listconf.py b/src/mailman/rest/listconf.py
index 6eb88e1fd..a6c15d428 100644
--- a/src/mailman/rest/listconf.py
+++ b/src/mailman/rest/listconf.py
@@ -24,8 +24,6 @@ __all__ = [
 
 from lazr.config import as_boolean, as_timedelta
 from mailman.config import config
-from mailman.core.errors import (
-    ReadOnlyPATCHRequestError, UnknownPATCHRequestError)
 from mailman.interfaces.action import Action
 from mailman.interfaces.archiver import ArchivePolicy
 from mailman.interfaces.autorespond import ResponseAction
@@ -35,7 +33,8 @@ from mailman.interfaces.mailinglist import (
 from mailman.rest.helpers import (
     GetterSetter, bad_request, etag, no_content, not_found, okay)
 from mailman.rest.validator import (
-    PatchValidator, Validator, enum_validator, list_of_strings_validator)
+    PatchValidator, ReadOnlyPATCHRequestError, UnknownPATCHRequestError,
+    Validator, enum_validator, list_of_strings_validator)
 
 
 
diff --git a/src/mailman/rest/users.py b/src/mailman/rest/users.py
index 238ec4562..21ed26745 100644
--- a/src/mailman/rest/users.py
+++ b/src/mailman/rest/users.py
@@ -28,8 +28,6 @@ __all__ = [
 
 from lazr.config import as_boolean
 from mailman.config import config
-from mailman.core.errors import (
-    ReadOnlyPATCHRequestError, UnknownPATCHRequestError)
 from mailman.interfaces.address import ExistingAddressError
 from mailman.interfaces.usermanager import IUserManager
 from mailman.rest.addresses import UserAddresses
@@ -38,7 +36,8 @@ from mailman.rest.helpers import (
     conflict, created, etag, forbidden, no_content, not_found, okay)
 from mailman.rest.preferences import Preferences
 from mailman.rest.validator import (
-    PatchValidator, Validator, list_of_strings_validator)
+    PatchValidator, ReadOnlyPATCHRequestError, UnknownPATCHRequestError,
+    Validator, list_of_strings_validator)
 from passlib.utils import generate_password as generate
 from zope.component import getUtility
 
diff --git a/src/mailman/rest/validator.py b/src/mailman/rest/validator.py
index 6b708872a..748a63d5c 100644
--- a/src/mailman/rest/validator.py
+++ b/src/mailman/rest/validator.py
@@ -27,9 +27,8 @@ __all__ = [
     ]
 
 
-from mailman.core.errors import (
-    ReadOnlyPATCHRequestError, UnknownPATCHRequestError)
 from mailman.interfaces.address import IEmailValidator
+from mailman.interfaces.errors import MailmanError
 from mailman.interfaces.languages import ILanguageManager
 from zope.component import getUtility
 
@@ -37,6 +36,24 @@ from zope.component import getUtility
 COMMASPACE = ', '
 
 
+class RESTError(MailmanError):
+    """Base class for REST API errors."""
+
+
+class UnknownPATCHRequestError(RESTError):
+    """A PATCH request contained an unknown attribute."""
+
+    def __init__(self, attribute):
+        self.attribute = attribute
+
+
+class ReadOnlyPATCHRequestError(RESTError):
+    """A PATCH request contained a read-only attribute."""
+
+    def __init__(self, attribute):
+        self.attribute = attribute
+
+
 
 class enum_validator:
     """Convert an enum value name into an enum value."""
diff --git a/src/mailman/utilities/i18n.py b/src/mailman/utilities/i18n.py
index 069bd8f52..3999af869 100644
--- a/src/mailman/utilities/i18n.py
+++ b/src/mailman/utilities/i18n.py
@@ -31,8 +31,8 @@ import sys
 from itertools import product
 from mailman.config import config
 from mailman.core.constants import system_preferences
-from mailman.core.errors import MailmanError
 from mailman.core.i18n import _
+from mailman.interfaces.errors import MailmanError
 from mailman.utilities.string import expand, wrap as wrap_text
 from pkg_resources import resource_filename
 
diff --git a/src/mailman/utilities/importer.py b/src/mailman/utilities/importer.py
index 782841838..3d1a8b82f 100644
--- a/src/mailman/utilities/importer.py
+++ b/src/mailman/utilities/importer.py
@@ -31,7 +31,6 @@ import logging
 import datetime
 
 from mailman.config import config
-from mailman.core.errors import MailmanError
 from mailman.handlers.decorate import decorate, decorate_template
 from mailman.interfaces.action import Action, FilterAction
 from mailman.interfaces.address import IEmailValidator
@@ -40,6 +39,7 @@ from mailman.interfaces.autorespond import ResponseAction
 from mailman.interfaces.bans import IBanManager
 from mailman.interfaces.bounce import UnrecognizedBounceDisposition
 from mailman.interfaces.digests import DigestFrequency
+from mailman.interfaces.errors import MailmanError
 from mailman.interfaces.languages import ILanguageManager
 from mailman.interfaces.mailinglist import (
     IAcceptableAliasSet, IHeaderMatchList)