text: """Read/write support for Maildir, mbox, MH, Babyl, and MMDF mailboxes."""
  
  # Notes for authors of new mailbox subclasses:
  #
  # Remember to fsync() changes to disk before closing a modified file
  # or returning from a flush() method.  See functions _sync_flush() and
  # _sync_close().
  
  import os
  import time
  import calendar
  import socket
  import errno
  import copy
  import warnings
  import email
  import email.message
  import email.generator
  import io
  import contextlib
  try:
      import fcntl
  except ImportError:
      fcntl = None
  
  __all__ = [ 'Mailbox', 'Maildir', 'mbox', 'MH', 'Babyl', 'MMDF',
              'Message', 'MaildirMessage', 'mboxMessage', 'MHMessage',
              'BabylMessage', 'MMDFMessage']
  
  linesep = os.linesep.encode('ascii')
  
  class Mailbox:
      """A group of messages in a particular place."""
  
      def __init__(self, path, factory=None, create=True):
          """Initialize a Mailbox instance."""
          self._path = os.path.abspath(os.path.expanduser(path))
          self._factory = factory
  
      def add(self, message):
          """Add message and return assigned key."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def remove(self, key):
          """Remove the keyed message; raise KeyError if it doesn't exist."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def __delitem__(self, key):
          self.remove(key)
  
      def discard(self, key):
          """If the keyed message exists, remove it."""
          try:
              self.remove(key)
          except KeyError:
              pass
  
      def __setitem__(self, key, message):
          """Replace the keyed message; raise KeyError if it doesn't exist."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def get(self, key, default=None):
          """Return the keyed message, or default if it doesn't exist."""
          try:
              return self.__getitem__(key)
          except KeyError:
              return default
  
      def __getitem__(self, key):
          """Return the keyed message; raise KeyError if it doesn't exist."""
          if not self._factory:
              return self.get_message(key)
          else:
              with contextlib.closing(self.get_file(key)) as file:
                  return self._factory(file)
  
      def get_message(self, key):
          """Return a Message representation or raise a KeyError."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def get_string(self, key):
          """Return a string representation or raise a KeyError.
  
          Uses email.message.Message to create a 7bit clean string
          representation of the message."""
          return email.message_from_bytes(self.get_bytes(key)).as_string()
  
      def get_bytes(self, key):
          """Return a byte string representation or raise a KeyError."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def get_file(self, key):
          """Return a file-like representation or raise a KeyError."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def iterkeys(self):
          """Return an iterator over keys."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def keys(self):
          """Return a list of keys."""
          return list(self.iterkeys())
  
      def itervalues(self):
          """Return an iterator over all messages."""
          for key in self.iterkeys():
              try:
                  value = self[key]
              except KeyError:
                  continue
              yield value
  
      def __iter__(self):
          return self.itervalues()
  
      def values(self):
          """Return a list of messages. Memory intensive."""
          return list(self.itervalues())
  
      def iteritems(self):
          """Return an iterator over (key, message) tuples."""
          for key in self.iterkeys():
              try:
                  value = self[key]
              except KeyError:
                  continue
              yield (key, value)
  
      def items(self):
          """Return a list of (key, message) tuples. Memory intensive."""
          return list(self.iteritems())
  
      def __contains__(self, key):
          """Return True if the keyed message exists, False otherwise."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def __len__(self):
          """Return a count of messages in the mailbox."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def clear(self):
          """Delete all messages."""
          for key in self.keys():
              self.discard(key)
  
      def pop(self, key, default=None):
          """Delete the keyed message and return it, or default."""
          try:
              result = self[key]
          except KeyError:
              return default
          self.discard(key)
          return result
  
      def popitem(self):
          """Delete an arbitrary (key, message) pair and return it."""
          for key in self.iterkeys():
              return (key, self.pop(key))     # This is only run once.
          else:
              raise KeyError('No messages in mailbox')
  
      def update(self, arg=None):
          """Change the messages that correspond to certain keys."""
          if hasattr(arg, 'iteritems'):
              source = arg.iteritems()
          elif hasattr(arg, 'items'):
              source = arg.items()
          else:
              source = arg
          bad_key = False
          for key, message in source:
              try:
                  self[key] = message
              except KeyError:
                  bad_key = True
          if bad_key:
              raise KeyError('No message with key(s)')
  
      def flush(self):
          """Write any pending changes to the disk."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def lock(self):
          """Lock the mailbox."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def unlock(self):
          """Unlock the mailbox if it is locked."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def close(self):
          """Flush and close the mailbox."""
          raise NotImplementedError('Method must be implemented by subclass')
  
      def _string_to_bytes(self, message):
          # If a message is not 7bit clean, we refuse to handle it since it
          # likely came from reading invalid messages in text mode, and that way
          # lies mojibake.
          try:
              return message.encode('ascii')
          except UnicodeError:
              raise ValueError("String input must be ASCII-only; "
                  "use bytes or a Message instead")
  
      # Whether each message must end in a newline
      _append_newline = False
  
      def _dump_message(self, message, target, mangle_from_=False):
          # This assumes the target file is open in binary mode.
          """Dump message contents to target file."""
          if isinstance(message, email.message.Message):
              buffer = io.BytesIO()
              gen = email.generator.BytesGenerator(buffer, mangle_from_, 0)
              gen.flatten(message)
              buffer.seek(0)
              data = buffer.read()
              data = data.replace(b'\n', linesep)
              target.write(data)
              if self._append_newline and not data.endswith(linesep):
                  # Make sure the message ends with a newline
                  target.write(linesep)
          elif isinstance(message, (str, bytes, io.StringIO)):
              if isinstance(message, io.StringIO):
                  warnings.warn("Use of StringIO input is deprecated, "
                      "use BytesIO instead", DeprecationWarning, 3)
                  message = message.getvalue()
              if isinstance(message, str):
                  message = self._string_to_bytes(message)
              if mangle_from_:
                  message = message.replace(b'\nFrom ', b'\n>From ')
              message = message.replace(b'\n', linesep)
              target.write(message)
              if self._append_newline and not message.endswith(linesep):
                  # Make sure the message ends with a newline
                  target.write(linesep)
          elif hasattr(message, 'read'):
              if hasattr(message, 'buffer'):
                  warnings.warn("Use of text mode files is deprecated, "
                      "use a binary mode file instead", DeprecationWarning, 3)
                  message = message.buffer
              lastline = None
              while True:
                  line = message.readline()
                  # Universal newline support.
                  if line.endswith(b'\r\n'):
                      line = line[:-2] + b'\n'
                  elif line.endswith(b'\r'):
                      line = line[:-1] + b'\n'
                  if not line:
                      break
                  if mangle_from_ and line.startswith(b'From '):
                      line = b'>From ' + line[5:]
                  line = line.replace(b'\n', linesep)
                  target.write(line)
                  lastline = line
              if self._append_newline and lastline and not lastline.endswith(linesep):
                  # Make sure the message ends with a newline
                  target.write(linesep)
          else:
              raise TypeError('Invalid message type: %s' % type(message))
  
  
  class Maildir(Mailbox):
      """A qmail-style Maildir mailbox."""
  
      colon = ':'
  
      def __init__(self, dirname, factory=None, create=True):
          """Initialize a Maildir instance."""
          Mailbox.__init__(self, dirname, factory, create)
          self._paths = {
              'tmp': os.path.join(self._path, 'tmp'),
              'new': os.path.join(self._path, 'new'),
              'cur': os.path.join(self._path, 'cur'),
              }
          if not os.path.exists(self._path):
              if create:
                  os.mkdir(self._path, 0o700)
                  for path in self._paths.values():
                      os.mkdir(path, 0o700)
              else:
                  raise NoSuchMailboxError(self._path)
          self._toc = {}
          self._toc_mtimes = {'cur': 0, 'new': 0}
          self._last_read = 0         # Records last time we read cur/new
          self._skewfactor = 0.1      # Adjust if os/fs clocks are skewing
  
      def add(self, message):
          """Add message and return assigned key."""
          tmp_file = self._create_tmp()
          try:
              self._dump_message(message, tmp_file)
          except BaseException:
              tmp_file.close()
              os.remove(tmp_file.name)
              raise
          _sync_close(tmp_file)
          if isinstance(message, MaildirMessage):
              subdir = message.get_subdir()
              suffix = self.colon + message.get_info()
              if suffix == self.colon:
                  suffix = ''
          else:
              subdir = 'new'
              suffix = ''
          uniq = os.path.basename(tmp_file.name).split(self.colon)[0]
          dest = os.path.join(self._path, subdir, uniq + suffix)
          if isinstance(message, MaildirMessage):
              os.utime(tmp_file.name,
                       (os.path.getatime(tmp_file.name), message.get_date()))
          # No file modification should be done after the file is moved to its
          # final position in order to prevent race conditions with changes
          # from other programs
          try:
              if hasattr(os, 'link'):
                  os.link(tmp_file.name, dest)
                  os.remove(tmp_file.name)
              else:
                  os.rename(tmp_file.name, dest)
          except OSError as e:
              os.remove(tmp_file.name)
              if e.errno == errno.EEXIST:
                  raise ExternalClashError('Name clash with existing message: %s'
                                           % dest)
              else:
                  raise
          return uniq
  
      def remove(self, key):
          """Remove the keyed message; raise KeyError if it doesn't exist."""
          os.remove(os.path.join(self._path, self._lookup(key)))
  
      def discard(self, key):
          """If the keyed message exists, remove it."""
          # This overrides an inapplicable implementation in the superclass.
          try:
              self.remove(key)
          except (KeyError, FileNotFoundError):
              pass
  
      def __setitem__(self, key, message):
          """Replace the keyed message; raise KeyError if it doesn't exist."""
          old_subpath = self._lookup(key)
          temp_key = self.add(message)
          temp_subpath = self._lookup(temp_key)
          if isinstance(message, MaildirMessage):
              # temp's subdir and suffix were specified by message.
              dominant_subpath = temp_subpath
          else:
              # temp's subdir and suffix were defaults from add().
              dominant_subpath = old_subpath
          subdir = os.path.dirname(dominant_subpath)
          if self.colon in dominant_subpath:
              suffix = self.colon + dominant_subpath.split(self.colon)[-1]
          else:
              suffix = ''
          self.discard(key)
          tmp_path = os.path.join(self._path, temp_subpath)
          new_path = os.path.join(self._path, subdir, key + suffix)
          if isinstance(message, MaildirMessage):
              os.utime(tmp_path,
                       (os.path.getatime(tmp_path), message.get_date()))
          # No file modification should be done after the file is moved to its
          # final position in order to prevent race conditions with changes
          # from other programs
          os.rename(tmp_path, new_path)
  
      def get_message(self, key):
          """Return a Message representation or raise a KeyError."""
          subpath = self._lookup(key)
          with open(os.path.join(self._path, subpath), 'rb') as f:
              if self._factory:
                  msg = self._factory(f)
              else:
                  msg = MaildirMessage(f)
          subdir, name = os.path.split(subpath)
          msg.set_subdir(subdir)
          if self.colon in name:
              msg.set_info(name.split(self.colon)[-1])
          msg.set_date(os.path.getmtime(os.path.join(self._path, subpath)))
          return msg
  
      def get_bytes(self, key):
          """Return a bytes representation or raise a KeyError."""
          with open(os.path.join(self._path, self._lookup(key)), 'rb') as f:
              return f.read().replace(linesep, b'\n')
  
      def get_file(self, key):
          """Return a file-like representation or raise a KeyError."""
          f = open(os.path.join(self._path, self._lookup(key)), 'rb')
          return _ProxyFile(f)
  
      def iterkeys(self):
          """Return an iterator over keys."""
          self._refresh()
          for key in self._toc:
              try:
                  self._lookup(key)
              except KeyError:
                  continue
              yield key
  
      def __contains__(self, key):
          """Return True if the keyed message exists, False otherwise."""
          self._refresh()
          return key in self._toc
  
      def __len__(self):
          """Return a count of messages in the mailbox."""
          self._refresh()
          return len(self._toc)
  
      def flush(self):
          """Write any pending changes to disk."""
          # Maildir changes are always written immediately, so there's nothing
          # to do.
          pass
  
      def lock(self):
          """Lock the mailbox."""
          return
  
      def unlock(self):
          """Unlock the mailbox if it is locked."""
          return
  
      def close(self):
          """Flush and close the mailbox."""
          return
  
      def list_folders(self):
          """Return a list of folder names."""
          result = []
          for entry in os.listdir(self._path):
              if len(entry) > 1 and entry[0] == '.' and \
                 os.path.isdir(os.path.join(self._path, entry)):
                  result.append(entry[1:])
          return result
  
      def get_folder(self, folder):
          """Return a Maildir instance for the named folder."""
          return Maildir(os.path.join(self._path, '.' + folder),
                         factory=self._factory,
                         create=False)
  
      def add_folder(self, folder):
          """Create a folder and return a Maildir instance representing it."""
          path = os.path.join(self._path, '.' + folder)
          result = Maildir(path, factory=self._factory)
          maildirfolder_path = os.path.join(path, 'maildirfolder')
          if not os.path.exists(maildirfolder_path):
              os.close(os.open(maildirfolder_path, os.O_CREAT | os.O_WRONLY,
                  0o666))
          return result
  
      def remove_folder(self, folder):
          """Delete the named folder, which must be empty."""
          path = os.path.join(self._path, '.' + folder)
          for entry in os.listdir(os.path.join(path, 'new')) + \
                       os.listdir(os.path.join(path, 'cur')):
              if len(entry) < 1 or entry[0] != '.':
                  raise NotEmptyError('Folder contains message(s): %s' % folder)
          for entry in os.listdir(path):
              if entry != 'new' and entry != 'cur' and entry != 'tmp' and \
                 os.path.isdir(os.path.join(path, entry)):
                  raise NotEmptyError("Folder contains subdirectory '%s': %s" %
                                      (folder, entry))
          for root, dirs, files in os.walk(path, topdown=False):
              for entry in files:
                  os.remove(os.path.join(root, entry))
              for entry in dirs:
                  os.rmdir(os.path.join(root, entry))
          os.rmdir(path)
  
      def clean(self):
          """Delete old files in "tmp"."""
          now = time.time()
          for entry in os.listdir(os.path.join(self._path, 'tmp')):
              path = os.path.join(self._path, 'tmp', entry)
              if now - os.path.getatime(path) > 129600:   # 60 * 60 * 36
                  os.remove(path)
  
      _count = 1  # This is used to generate unique file names.
  
      def _create_tmp(self):
          """Create a file in the tmp subdirectory and open and return it."""
          now = time.time()
          hostname = socket.gethostname()
          if '/' in hostname:
              hostname = hostname.replace('/', r'\057')
          if ':' in hostname:
              hostname = hostname.replace(':', r'\072')
          uniq = "%s.M%sP%sQ%s.%s" % (int(now), int(now % 1 * 1e6), os.getpid(),
                                      Maildir._count, hostname)
          path = os.path.join(self._path, 'tmp', uniq)
          try:
              os.stat(path)
          except FileNotFoundError:
              Maildir._count += 1
              try:
                  return _create_carefully(path)
              except FileExistsError:
                  pass
  
          # Fall through to here if stat succeeded or open raised EEXIST.
          raise ExternalClashError('Name clash prevented file creation: %s' %
                                   path)
  
      def _refresh(self):
          """Update table of contents mapping."""
          # If it has been less than two seconds since the last _refresh() call,
          # we have to unconditionally re-read the mailbox just in case it has
          # been modified, because os.path.mtime() has a 2 sec resolution in the
          # most common worst case (FAT) and a 1 sec resolution typically.  This
          # results in a few unnecessary re-reads when _refresh() is called
          # multiple times in that interval, but once the clock ticks over, we
          # will only re-read as needed.  Because the filesystem might be being
          # served by an independent system with its own clock, we record and
          # compare with the mtimes from the filesystem.  Because the other
          # system's clock might be skewing relative to our clock, we add an
          # extra delta to our wait.  The default is one tenth second, but is an
          # instance variable and so can be adjusted if dealing with a
          # particularly skewed or irregular system.
          if time.time() - self._last_read > 2 + self._skewfactor:
              refresh = False
              for subdir in self._toc_mtimes:
                  mtime = os.path.getmtime(self._paths[subdir])
                  if mtime > self._toc_mtimes[subdir]:
                      refresh = True
                  self._toc_mtimes[subdir] = mtime
              if not refresh:
                  return
          # Refresh toc
          self._toc = {}
          for subdir in self._toc_mtimes:
              path = self._paths[subdir]
              for entry in os.listdir(path):
                  p = os.path.join(path, entry)
                  if os.path.isdir(p):
                      continue
                  uniq = entry.split(self.colon)[0]
                  self._toc[uniq] = os.path.join(subdir, entry)
          self._last_read = time.time()
  
      def _lookup(self, key):
          """Use TOC to return subpath for given key, or raise a KeyError."""
          try:
              if os.path.exists(os.path.join(self._path, self._toc[key])):
                  return self._toc[key]
          except KeyError:
              pass
          self._refresh()
          try:
              return self._toc[key]
          except KeyError:
              raise KeyError('No message with key: %s' % key)
  
      # This method is for backward compatibility only.
      def next(self):
          """Return the next message in a one-time iteration."""
          if not hasattr(self, '_onetime_keys'):
              self._onetime_keys = self.iterkeys()
          while True:
              try:
                  return self[next(self._onetime_keys)]
              except StopIteration:
                  return None
              except KeyError:
                  continue
  
  
  class _singlefileMailbox(Mailbox):
      """A single-file mailbox."""
  
      def __init__(self, path, factory=None, create=True):
          """Initialize a single-file mailbox."""
          Mailbox.__init__(self, path, factory, create)
          try:
              f = open(self._path, 'rb+')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  if create:
                      f = open(self._path, 'wb+')
                  else:
                      raise NoSuchMailboxError(self._path)
              elif e.errno in (errno.EACCES, errno.EROFS):
                  f = open(self._path, 'rb')
              else:
                  raise
          self._file = f
          self._toc = None
          self._next_key = 0
          self._pending = False       # No changes require rewriting the file.
          self._pending_sync = False  # No need to sync the file
          self._locked = False
          self._file_length = None    # Used to record mailbox size
  
      def add(self, message):
          """Add message and return assigned key."""
          self._lookup()
          self._toc[self._next_key] = self._append_message(message)
          self._next_key += 1
          # _append_message appends the message to the mailbox file. We
          # don't need a full rewrite + rename, sync is enough.
          self._pending_sync = True
          return self._next_key - 1
  
      def remove(self, key):
          """Remove the keyed message; raise KeyError if it doesn't exist."""
          self._lookup(key)
          del self._toc[key]
          self._pending = True
  
      def __setitem__(self, key, message):
          """Replace the keyed message; raise KeyError if it doesn't exist."""
          self._lookup(key)
          self._toc[key] = self._append_message(message)
          self._pending = True
  
      def iterkeys(self):
          """Return an iterator over keys."""
          self._lookup()
          yield from self._toc.keys()
  
      def __contains__(self, key):
          """Return True if the keyed message exists, False otherwise."""
          self._lookup()
          return key in self._toc
  
      def __len__(self):
          """Return a count of messages in the mailbox."""
          self._lookup()
          return len(self._toc)
  
      def lock(self):
          """Lock the mailbox."""
          if not self._locked:
              _lock_file(self._file)
              self._locked = True
  
      def unlock(self):
          """Unlock the mailbox if it is locked."""
          if self._locked:
              _unlock_file(self._file)
              self._locked = False
  
      def flush(self):
          """Write any pending changes to disk."""
          if not self._pending:
              if self._pending_sync:
                  # Messages have only been added, so syncing the file
                  # is enough.
                  _sync_flush(self._file)
                  self._pending_sync = False
              return
  
          # In order to be writing anything out at all, self._toc must
          # already have been generated (and presumably has been modified
          # by adding or deleting an item).
          assert self._toc is not None
  
          # Check length of self._file; if it's changed, some other process
          # has modified the mailbox since we scanned it.
          self._file.seek(0, 2)
          cur_len = self._file.tell()
          if cur_len != self._file_length:
              raise ExternalClashError('Size of mailbox file changed '
                                       '(expected %i, found %i)' %
                                       (self._file_length, cur_len))
  
          new_file = _create_temporary(self._path)
          try:
              new_toc = {}
              self._pre_mailbox_hook(new_file)
              for key in sorted(self._toc.keys()):
                  start, stop = self._toc[key]
                  self._file.seek(start)
                  self._pre_message_hook(new_file)
                  new_start = new_file.tell()
                  while True:
                      buffer = self._file.read(min(4096,
                                                   stop - self._file.tell()))
                      if not buffer:
                          break
                      new_file.write(buffer)
                  new_toc[key] = (new_start, new_file.tell())
                  self._post_message_hook(new_file)
              self._file_length = new_file.tell()
          except:
              new_file.close()
              os.remove(new_file.name)
              raise
          _sync_close(new_file)
          # self._file is about to get replaced, so no need to sync.
          self._file.close()
          # Make sure the new file's mode is the same as the old file's
          mode = os.stat(self._path).st_mode
          os.chmod(new_file.name, mode)
          try:
              os.rename(new_file.name, self._path)
          except FileExistsError:
              os.remove(self._path)
              os.rename(new_file.name, self._path)
          self._file = open(self._path, 'rb+')
          self._toc = new_toc
          self._pending = False
          self._pending_sync = False
          if self._locked:
              _lock_file(self._file, dotlock=False)
  
      def _pre_mailbox_hook(self, f):
          """Called before writing the mailbox to file f."""
          return
  
      def _pre_message_hook(self, f):
          """Called before writing each message to file f."""
          return
  
      def _post_message_hook(self, f):
          """Called after writing each message to file f."""
          return
  
      def close(self):
          """Flush and close the mailbox."""
          self.flush()
          if self._locked:
              self.unlock()
          self._file.close()  # Sync has been done by self.flush() above.
  
      def _lookup(self, key=None):
          """Return (start, stop) or raise KeyError."""
          if self._toc is None:
              self._generate_toc()
          if key is not None:
              try:
                  return self._toc[key]
              except KeyError:
                  raise KeyError('No message with key: %s' % key)
  
      def _append_message(self, message):
          """Append message to mailbox and return (start, stop) offsets."""
          self._file.seek(0, 2)
          before = self._file.tell()
          if len(self._toc) == 0 and not self._pending:
              # This is the first message, and the _pre_mailbox_hook
              # hasn't yet been called. If self._pending is True,
              # messages have been removed, so _pre_mailbox_hook must
              # have been called already.
              self._pre_mailbox_hook(self._file)
          try:
              self._pre_message_hook(self._file)
              offsets = self._install_message(message)
              self._post_message_hook(self._file)
          except BaseException:
              self._file.truncate(before)
              raise
          self._file.flush()
          self._file_length = self._file.tell()  # Record current length of mailbox
          return offsets
  
  
  
  class _mboxMMDF(_singlefileMailbox):
      """An mbox or MMDF mailbox."""
  
      _mangle_from_ = True
  
      def get_message(self, key):
          """Return a Message representation or raise a KeyError."""
          start, stop = self._lookup(key)
          self._file.seek(start)
          from_line = self._file.readline().replace(linesep, b'')
          string = self._file.read(stop - self._file.tell())
          msg = self._message_factory(string.replace(linesep, b'\n'))
          msg.set_from(from_line[5:].decode('ascii'))
          return msg
  
      def get_string(self, key, from_=False):
          """Return a string representation or raise a KeyError."""
          return email.message_from_bytes(
              self.get_bytes(key)).as_string(unixfrom=from_)
  
      def get_bytes(self, key, from_=False):
          """Return a string representation or raise a KeyError."""
          start, stop = self._lookup(key)
          self._file.seek(start)
          if not from_:
              self._file.readline()
          string = self._file.read(stop - self._file.tell())
          return string.replace(linesep, b'\n')
  
      def get_file(self, key, from_=False):
          """Return a file-like representation or raise a KeyError."""
          start, stop = self._lookup(key)
          self._file.seek(start)
          if not from_:
              self._file.readline()
          return _PartialFile(self._file, self._file.tell(), stop)
  
      def _install_message(self, message):
          """Format a message and blindly write to self._file."""
          from_line = None
          if isinstance(message, str):
              message = self._string_to_bytes(message)
          if isinstance(message, bytes) and message.startswith(b'From '):
              newline = message.find(b'\n')
              if newline != -1:
                  from_line = message[:newline]
                  message = message[newline + 1:]
              else:
                  from_line = message
                  message = b''
          elif isinstance(message, _mboxMMDFMessage):
              author = message.get_from().encode('ascii')
              from_line = b'From ' + author
          elif isinstance(message, email.message.Message):
              from_line = message.get_unixfrom()  # May be None.
              if from_line is not None:
                  from_line = from_line.encode('ascii')
          if from_line is None:
              from_line = b'From MAILER-DAEMON ' + time.asctime(time.gmtime()).encode()
          start = self._file.tell()
          self._file.write(from_line + linesep)
          self._dump_message(message, self._file, self._mangle_from_)
          stop = self._file.tell()
          return (start, stop)
  
  
  class mbox(_mboxMMDF):
      """A classic mbox mailbox."""
  
      _mangle_from_ = True
  
      # All messages must end in a newline character, and
      # _post_message_hooks outputs an empty line between messages.
      _append_newline = True
  
      def __init__(self, path, factory=None, create=True):
          """Initialize an mbox mailbox."""
          self._message_factory = mboxMessage
          _mboxMMDF.__init__(self, path, factory, create)
  
      def _post_message_hook(self, f):
          """Called after writing each message to file f."""
          f.write(linesep)
  
      def _generate_toc(self):
          """Generate key-to-(start, stop) table of contents."""
          starts, stops = [], []
          last_was_empty = False
          self._file.seek(0)
          while True:
              line_pos = self._file.tell()
              line = self._file.readline()
              if line.startswith(b'From '):
                  if len(stops) < len(starts):
                      if last_was_empty:
                          stops.append(line_pos - len(linesep))
                      else:
                          # The last line before the "From " line wasn't
                          # blank, but we consider it a start of a
                          # message anyway.
                          stops.append(line_pos)
                  starts.append(line_pos)
                  last_was_empty = False
              elif not line:
                  if last_was_empty:
                      stops.append(line_pos - len(linesep))
                  else:
                      stops.append(line_pos)
                  break
              elif line == linesep:
                  last_was_empty = True
              else:
                  last_was_empty = False
          self._toc = dict(enumerate(zip(starts, stops)))
          self._next_key = len(self._toc)
          self._file_length = self._file.tell()
  
  
  class MMDF(_mboxMMDF):
      """An MMDF mailbox."""
  
      def __init__(self, path, factory=None, create=True):
          """Initialize an MMDF mailbox."""
          self._message_factory = MMDFMessage
          _mboxMMDF.__init__(self, path, factory, create)
  
      def _pre_message_hook(self, f):
          """Called before writing each message to file f."""
          f.write(b'\001\001\001\001' + linesep)
  
      def _post_message_hook(self, f):
          """Called after writing each message to file f."""
          f.write(linesep + b'\001\001\001\001' + linesep)
  
      def _generate_toc(self):
          """Generate key-to-(start, stop) table of contents."""
          starts, stops = [], []
          self._file.seek(0)
          next_pos = 0
          while True:
              line_pos = next_pos
              line = self._file.readline()
              next_pos = self._file.tell()
              if line.startswith(b'\001\001\001\001' + linesep):
                  starts.append(next_pos)
                  while True:
                      line_pos = next_pos
                      line = self._file.readline()
                      next_pos = self._file.tell()
                      if line == b'\001\001\001\001' + linesep:
                          stops.append(line_pos - len(linesep))
                          break
                      elif not line:
                          stops.append(line_pos)
                          break
              elif not line:
                  break
          self._toc = dict(enumerate(zip(starts, stops)))
          self._next_key = len(self._toc)
          self._file.seek(0, 2)
          self._file_length = self._file.tell()
  
  
  class MH(Mailbox):
      """An MH mailbox."""
  
      def __init__(self, path, factory=None, create=True):
          """Initialize an MH instance."""
          Mailbox.__init__(self, path, factory, create)
          if not os.path.exists(self._path):
              if create:
                  os.mkdir(self._path, 0o700)
                  os.close(os.open(os.path.join(self._path, '.mh_sequences'),
                                   os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600))
              else:
                  raise NoSuchMailboxError(self._path)
          self._locked = False
  
      def add(self, message):
          """Add message and return assigned key."""
          keys = self.keys()
          if len(keys) == 0:
              new_key = 1
          else:
              new_key = max(keys) + 1
          new_path = os.path.join(self._path, str(new_key))
          f = _create_carefully(new_path)
          closed = False
          try:
              if self._locked:
                  _lock_file(f)
              try:
                  try:
                      self._dump_message(message, f)
                  except BaseException:
                      # Unlock and close so it can be deleted on Windows
                      if self._locked:
                          _unlock_file(f)
                      _sync_close(f)
                      closed = True
                      os.remove(new_path)
                      raise
                  if isinstance(message, MHMessage):
                      self._dump_sequences(message, new_key)
              finally:
                  if self._locked:
                      _unlock_file(f)
          finally:
              if not closed:
                  _sync_close(f)
          return new_key
  
      def remove(self, key):
          """Remove the keyed message; raise KeyError if it doesn't exist."""
          path = os.path.join(self._path, str(key))
          try:
              f = open(path, 'rb+')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  raise KeyError('No message with key: %s' % key)
              else:
                  raise
          else:
              f.close()
              os.remove(path)
  
      def __setitem__(self, key, message):
          """Replace the keyed message; raise KeyError if it doesn't exist."""
          path = os.path.join(self._path, str(key))
          try:
              f = open(path, 'rb+')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  raise KeyError('No message with key: %s' % key)
              else:
                  raise
          try:
              if self._locked:
                  _lock_file(f)
              try:
                  os.close(os.open(path, os.O_WRONLY | os.O_TRUNC))
                  self._dump_message(message, f)
                  if isinstance(message, MHMessage):
                      self._dump_sequences(message, key)
              finally:
                  if self._locked:
                      _unlock_file(f)
          finally:
              _sync_close(f)
  
      def get_message(self, key):
          """Return a Message representation or raise a KeyError."""
          try:
              if self._locked:
                  f = open(os.path.join(self._path, str(key)), 'rb+')
              else:
                  f = open(os.path.join(self._path, str(key)), 'rb')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  raise KeyError('No message with key: %s' % key)
              else:
                  raise
          with f:
              if self._locked:
                  _lock_file(f)
              try:
                  msg = MHMessage(f)
              finally:
                  if self._locked:
                      _unlock_file(f)
          for name, key_list in self.get_sequences().items():
              if key in key_list:
                  msg.add_sequence(name)
          return msg
  
      def get_bytes(self, key):
          """Return a bytes representation or raise a KeyError."""
          try:
              if self._locked:
                  f = open(os.path.join(self._path, str(key)), 'rb+')
              else:
                  f = open(os.path.join(self._path, str(key)), 'rb')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  raise KeyError('No message with key: %s' % key)
              else:
                  raise
          with f:
              if self._locked:
                  _lock_file(f)
              try:
                  return f.read().replace(linesep, b'\n')
              finally:
                  if self._locked:
                      _unlock_file(f)
  
      def get_file(self, key):
          """Return a file-like representation or raise a KeyError."""
          try:
              f = open(os.path.join(self._path, str(key)), 'rb')
          except OSError as e:
              if e.errno == errno.ENOENT:
                  raise KeyError('No message with key: %s' % key)
              else:
                  raise
          return _ProxyFile(f)
  
      def iterkeys(self):
          """Return an iterator over keys."""
          return iter(sorted(int(entry) for entry in os.listdir(self._path)
                                        if entry.isdigit()))
  
      def __contains__(self, key):
          """Return True if the keyed message exists, False otherwise."""
          return os.path.exists(os.path.join(self._path, str(key)))
  
      def __len__(self):
          """Return a count of messages in the mailbox."""
          return len(list(self.iterkeys()))
  
      def lock(self):
          """Lock the mailbox."""
          if not self._locked:
              self._file = open(os.path.join(self._path, '.mh_sequences'), 'rb+')
              _lock_file(self._file)
              self._locked = True
  
      def unlock(self):
          """Unlock the mailbox if it is locked."""
          if self._locked:
              _unlock_file(self._file)
              _sync_close(self._file)
              del self._file
              self._locked = False
  
      def flush(self):
          """Write any pending changes to the disk."""
          return
  
      def close(self):
          """Flush and close the mailbox."""
          if self._locked:
              self.unlock()
  
      def list_folders(self):
          """Return a list of folder names."""
          result = []
          for entry in os.listdir(self._path):
              if os.path.isdir(os.path.join(self._path, entry)):
                  result.append(entry)
          return result
  
      def get_folder(self, folder):
          """Return an MH instance for the named folder."""
          return MH(os.path.join(self._path, folder),
                    factory=self._factory, create=False)
  
      def add_folder(self, folder):
          """Create a folder and return an MH instance representing it."""
          return MH(os.path.join(self._path, folder),
                    factory=self._factory)
  
      def remove_folder(self, folder):
          """Delete the named folder, which must be empty."""
          path = os.path.join(self._path, folder)
          entries = os.listdir(path)
          if entries == ['.mh_sequences']:
              os.remove(os.path.join(path, '.mh_sequences'))
          elif entries == []:
              pass
          else:
              raise NotEmptyError('Folder not empty: %s' % self._path)
          os.rmdir(path)
  
      def get_sequences(self):
          """Return a name-to-key-list dictionary to define each sequence."""
          results = {}
          with open(os.path.join(self._path, '.mh_sequences'), 'r', encoding='ASCII') as f:
              all_keys = set(self.keys())
              for line in f:
                  try:
                      name, contents = line.split(':')
                      keys = set()
                      for spec in contents.split():
                          if spec.isdigit():
                              keys.add(int(spec))
                          else:
                              start, stop = (int(x) for x in spec.split('-'))
                              keys.update(range(start, stop + 1))
                      results[name] = [key for key in sorted(keys) \
                                           if key in all_keys]
                      if len(results[name]) == 0:
                          del results[name]
                  except ValueError:
                      raise FormatError('Invalid sequence specification: %s' %
                                        line.rstrip())
          return results
  
      def set_sequences(self, sequences):
          """Set sequences using the given name-to-key-list dictionary."""
          f = open(os.path.join(self._path, '.mh_sequences'), 'r+', encoding='ASCII')
          try:
              os.close(os.open(f.name, os.O_WRONLY | os.O_TRUNC))
              for name, keys in sequences.items():
                  if len(keys) == 0:
                      continue
                  f.write(name + ':')
                  prev = None
                  completing = False
                  for key in sorted(set(keys)):
                      if key - 1 == prev:
                          if not completing:
                              completing = True
                              f.write('-')
                      elif completing:
                          completing = False
                          f.write('%s %s' % (prev, key))
                      else:
                          f.write(' %s' % key)
                      prev = key
                  if completing:
                      f.write(str(prev) + '\n')
                  else:
                      f.write('\n')
          finally:
              _sync_close(f)
  
      def pack(self):
          """Re-name messages to eliminate numbering gaps. Invalidates keys."""
          sequences = self.get_sequences()
          prev = 0
          changes = []
          for key in self.iterkeys():
              if key - 1 != prev:
                  changes.append((key, prev + 1))
                  if hasattr(os, 'link'):
                      os.link(os.path.join(self._path, str(key)),
                              os.path.join(self._path, str(prev + 1)))
                      os.unlink(os.path.join(self._path, str(key)))
                  else:
                      os.rename(os.path.join(self._path, str(key)),
                                os.path.join(self._path, str(prev + 1)))
              prev += 1
          self._next_key = prev + 1
          if len(changes) == 0:
              return
          for name, key_list in sequences.items():
              for old, new in changes:
                  if old in key_list:
                      key_list[key_list.index(old)] = new
          self.set_sequences(sequences)
  
      def _dump_sequences(self, message, key):
          """Inspect a new MHMessage and update sequences appropriately."""
          pending_sequences = message.get_sequences()
          all_sequences = self.get_sequences()
          for name, key_list in all_sequences.items():
              if name in pending_sequences:
                  key_list.append(key)
              elif key in key_list:
                  del key_list[key_list.index(key)]
          for sequence in pending_sequences:
              if sequence not in all_sequences:
                  all_sequences[sequence] = [key]
          self.set_sequences(all_sequences)
  
  
  class Babyl(_singlefileMailbox):
      """An Rmail-style Babyl mailbox."""
  
      _special_labels = frozenset(('unseen', 'deleted', 'filed', 'answered',
                                   'forwarded', 'edited', 'resent'))
  
      def __init__(self, path, factory=None, create=True):
          """Initialize a Babyl mailbox."""
          _singlefileMailbox.__init__(self, path, factory, create)
          self._labels = {}
  
      def add(self, message):
          """Add message and return assigned key."""
          key = _singlefileMailbox.add(self, message)
          if isinstance(message, BabylMessage):
              self._labels[key] = message.get_labels()
          return key
  
      def remove(self, key):
          """Remove the keyed message; raise KeyError if it doesn't exist."""
          _singlefileMailbox.remove(self, key)
          if key in self._labels:
              del self._labels[key]
  
      def __setitem__(self, key, message):
          """Replace the keyed message; raise KeyError if it doesn't exist."""
          _singlefileMailbox.__setitem__(self, key, message)
          if isinstance(message, BabylMessage):
              self._labels[key] = message.get_labels()
  
      def get_message(self, key):
          """Return a Message representation or raise a KeyError."""
          start, stop = self._lookup(key)
          self._file.seek(start)
          self._file.readline()   # Skip b'1,' line specifying labels.
          original_headers = io.BytesIO()
          while True:
              line = self._file.readline()
              if line == b'*** EOOH ***' + linesep or not line:
                  break
              original_headers.write(line.replace(linesep, b'\n'))
          visible_headers = io.BytesIO()
          while True:
              line = self._file.readline()
              if line == linesep or not line:
                  break
              visible_headers.write(line.replace(linesep, b'\n'))
          # Read up to the stop, or to the end
          n = stop - self._file.tell()
          assert n >= 0
          body = self._file.read(n)
          body = body.replace(linesep, b'\n')
          msg = BabylMessage(original_headers.getvalue() + body)
          msg.set_visible(visible_headers.getvalue())
          if key in self._labels:
              msg.set_labels(self._labels[key])
          return msg
  
      def get_bytes(self, key):
          """Return a string representation or raise a KeyError."""
          start, stop = self._lookup(key)
          self._file.seek(start)
          self._file.readline()   # Skip b'1,' line specifying labels.
          original_headers = io.BytesIO()
          while True:
              line = self._file.readline()
              if line == b'*** EOOH ***' + linesep or not line:
                  break
              original_headers.write(line.replace(linesep, b'\n'))
          while True:
              line = self._file.readline()
              if line == linesep or not line:
                  break
          headers = original_headers.getvalue()
          n = stop - self._file.tell()
          assert n >= 0
          data = self._file.read(n)
          data = data.replace(linesep, b'\n')
          return headers + data
  
      def get_file(self, key):
          """Return a file-like representation or raise a KeyError."""
          return io.BytesIO(self.get_bytes(key).replace(b'\n', linesep))
  
      def get_labels(self):
          """Return a list of user-defined labels in the mailbox."""
          self._lookup()
          labels = set()
          for label_list in self._labels.values():
              labels.update(label_list)
          labels.difference_update(self._special_labels)
          return list(labels)
  
      def _generate_toc(self):
          """Generate key-to-(start, stop) table of contents."""
          starts, stops = [], []
          self._file.seek(0)
          next_pos = 0
          label_lists = []
          while True:
              line_pos = next_pos
              line = self._file.readline()
              next_pos = self._file.tell()
              if line == b'\037\014' + linesep:
                  if len(stops) < len(starts):
                      stops.append(line_pos - len(linesep))
                  starts.append(next_pos)
                  labels = [label.strip() for label
                                          in self._file.readline()[1:].split(b',')
                                          if label.strip()]
                  label_lists.append(labels)
              elif line == b'\037' or line == b'\037' + linesep:
                  if len(stops) < len(starts):
                      stops.append(line_pos - len(linesep))
              elif not line:
                  stops.append(line_pos - len(linesep))
                  break
          self._toc = dict(enumerate(zip(starts, stops)))
          self._labels = dict(enumerate(label_lists))
          self._next_key = len(self._toc)
          self._file.seek(0, 2)
          self._file_length = self._file.tell()
  
      def _pre_mailbox_hook(self, f):
          """Called before writing the mailbox to file f."""
          babyl = b'BABYL OPTIONS:' + linesep
          babyl += b'Version: 5' + linesep
          labels = self.get_labels()
          labels = (label.encode() for label in labels)
          babyl += b'Labels:' + b','.join(labels) + linesep
          babyl += b'\037'
          f.write(babyl)
  
      def _pre_message_hook(self, f):
          """Called before writing each message to file f."""
          f.write(b'\014' + linesep)
  
      def _post_message_hook(self, f):
          """Called after writing each message to file f."""
          f.write(linesep + b'\037')
  
      def _install_message(self, message):
          """Write message contents and return (start, stop)."""
          start = self._file.tell()
          if isinstance(message, BabylMessage):
              special_labels = []
              labels = []
              for label in message.get_labels():
                  if label in self._special_labels:
                      special_labels.append(label)
                  else:
                      labels.append(label)
              self._file.write(b'1')
              for label in special_labels:
                  self._file.write(b', ' + label.encode())
              self._file.write(b',,')
              for label in labels:
                  self._file.write(b' ' + label.encode() + b',')
              self._file.write(linesep)
          else:
              self._file.write(b'1,,' + linesep)
          if isinstance(message, email.message.Message):
              orig_buffer = io.BytesIO()
              orig_generator = email.generator.BytesGenerator(orig_buffer, False, 0)
              orig_generator.flatten(message)
              orig_buffer.seek(0)
              while True:
                  line = orig_buffer.readline()
                  self._file.write(line.replace(b'\n', linesep))
                  if line == b'\n' or not line:
                      break
              self._file.write(b'*** EOOH ***' + linesep)
              if isinstance(message, BabylMessage):
                  vis_buffer = io.BytesIO()
                  vis_generator = email.generator.BytesGenerator(vis_buffer, False, 0)
                  vis_generator.flatten(message.get_visible())
                  while True:
                      line = vis_buffer.readline()
                      self._file.write(line.replace(b'\n', linesep))
                      if line == b'\n' or not line:
                          break
              else:
                  orig_buffer.seek(0)
                  while True:
                      line = orig_buffer.readline()
                      self._file.write(line.replace(b'\n', linesep))
                      if line == b'\n' or not line:
                          break
              while True:
                  buffer = orig_buffer.read(4096) # Buffer size is arbitrary.
                  if not buffer:
                      break
                  self._file.write(buffer.replace(b'\n', linesep))
          elif isinstance(message, (bytes, str, io.StringIO)):
              if isinstance(message, io.StringIO):
                  warnings.warn("Use of StringIO input is deprecated, "
                      "use BytesIO instead", DeprecationWarning, 3)
                  message = message.getvalue()
              if isinstance(message, str):
                  message = self._string_to_bytes(message)
              body_start = message.find(b'\n\n') + 2
              if body_start - 2 != -1:
                  self._file.write(message[:body_start].replace(b'\n', linesep))
                  self._file.write(b'*** EOOH ***' + linesep)
                  self._file.write(message[:body_start].replace(b'\n', linesep))
                  self._file.write(message[body_start:].replace(b'\n', linesep))
              else:
                  self._file.write(b'*** EOOH ***' + linesep + linesep)
                  self._file.write(message.replace(b'\n', linesep))
          elif hasattr(message, 'readline'):
              if hasattr(message, 'buffer'):
                  warnings.warn("Use of text mode files is deprecated, "
                      "use a binary mode file instead", DeprecationWarning, 3)
                  message = message.buffer
              original_pos = message.tell()
              first_pass = True
              while True:
                  line = message.readline()
                  # Universal newline support.
                  if line.endswith(b'\r\n'):
                      line = line[:-2] + b'\n'
                  elif line.endswith(b'\r'):
                      line = line[:-1] + b'\n'
                  self._file.write(line.replace(b'\n', linesep))
                  if line == b'\n' or not line:
                      if first_pass:
                          first_pass = False
                          self._file.write(b'*** EOOH ***' + linesep)
                          message.seek(original_pos)
                      else:
                          break
              while True:
                  line = message.readline()
                  if not line:
                      break
                  # Universal newline support.
                  if line.endswith(b'\r\n'):
                      line = line[:-2] + linesep
                  elif line.endswith(b'\r'):
                      line = line[:-1] + linesep
                  elif line.endswith(b'\n'):
                      line = line[:-1] + linesep
                  self._file.write(line)
          else:
              raise TypeError('Invalid message type: %s' % type(message))
          stop = self._file.tell()
          return (start, stop)
  
  
  class Message(email.message.Message):
      """Message with mailbox-format-specific properties."""
  
      def __init__(self, message=None):
          """Initialize a Message instance."""
          if isinstance(message, email.message.Message):
              self._become_message(copy.deepcopy(message))
              if isinstance(message, Message):
                  message._explain_to(self)
          elif isinstance(message, bytes):
              self._become_message(email.message_from_bytes(message))
          elif isinstance(message, str):
              self._become_message(email.message_from_string(message))
          elif isinstance(message, io.TextIOWrapper):
              self._become_message(email.message_from_file(message))
          elif hasattr(message, "read"):
              self._become_message(email.message_from_binary_file(message))
          elif message is None:
              email.message.Message.__init__(self)
          else:
              raise TypeError('Invalid message type: %s' % type(message))
  
      def _become_message(self, message):
          """Assume the non-format-specific state of message."""
          type_specific = getattr(message, '_type_specific_attributes', [])
          for name in message.__dict__:
              if name not in type_specific:
                  self.__dict__[name] = message.__dict__[name]
  
      def _explain_to(self, message):
          """Copy format-specific state to message insofar as possible."""
          if isinstance(message, Message):
              return  # There's nothing format-specific to explain.
          else:
              raise TypeError('Cannot convert to specified type')
  
  
  class MaildirMessage(Message):
      """Message with Maildir-specific properties."""
  
      _type_specific_attributes = ['_subdir', '_info', '_date']
  
      def __init__(self, message=None):
          """Initialize a MaildirMessage instance."""
          self._subdir = 'new'
          self._info = ''
          self._date = time.time()
          Message.__init__(self, message)
  
      def get_subdir(self):
          """Return 'new' or 'cur'."""
          return self._subdir
  
      def set_subdir(self, subdir):
          """Set subdir to 'new' or 'cur'."""
          if subdir == 'new' or subdir == 'cur':
              self._subdir = subdir
          else:
              raise ValueError("subdir must be 'new' or 'cur': %s" % subdir)
  
      def get_flags(self):
          """Return as a string the flags that are set."""
          if self._info.startswith('2,'):
              return self._info[2:]
          else:
              return ''
  
      def set_flags(self, flags):
          """Set the given flags and unset all others."""
          self._info = '2,' + ''.join(sorted(flags))
  
      def add_flag(self, flag):
          """Set the given flag(s) without changing others."""
          self.set_flags(''.join(set(self.get_flags()) | set(flag)))
  
      def remove_flag(self, flag):
          """Unset the given string flag(s) without changing others."""
          if self.get_flags():
              self.set_flags(''.join(set(self.get_flags()) - set(flag)))
  
      def get_date(self):
          """Return delivery date of message, in seconds since the epoch."""
          return self._date
  
      def set_date(self, date):
          """Set delivery date of message, in seconds since the epoch."""
          try:
              self._date = float(date)
          except ValueError:
              raise TypeError("can't convert to float: %s" % date)
  
      def get_info(self):
          """Get the message's "info" as a string."""
          return self._info
  
      def set_info(self, info):
          """Set the message's "info" string."""
          if isinstance(info, str):
              self._info = info
          else:
              raise TypeError('info must be a string: %s' % type(info))
  
      def _explain_to(self, message):
          """Copy Maildir-specific state to message insofar as possible."""
          if isinstance(message, MaildirMessage):
              message.set_flags(self.get_flags())
              message.set_subdir(self.get_subdir())
              message.set_date(self.get_date())
          elif isinstance(message, _mboxMMDFMessage):
              flags = set(self.get_flags())
              if 'S' in flags:
                  message.add_flag('R')
              if self.get_subdir() == 'cur':
                  message.add_flag('O')
              if 'T' in flags:
                  message.add_flag('D')
              if 'F' in flags:
                  message.add_flag('F')
              if 'R' in flags:
                  message.add_flag('A')
              message.set_from('MAILER-DAEMON', time.gmtime(self.get_date()))
          elif isinstance(message, MHMessage):
              flags = set(self.get_flags())
              if 'S' not in flags:
                  message.add_sequence('unseen')
              if 'R' in flags:
                  message.add_sequence('replied')
              if 'F' in flags:
                  message.add_sequence('flagged')
          elif isinstance(message, BabylMessage):
              flags = set(self.get_flags())
              if 'S' not in flags:
                  message.add_label('unseen')
              if 'T' in flags:
                  message.add_label('deleted')
              if 'R' in flags:
                  message.add_label('answered')
              if 'P' in flags:
                  message.add_label('forwarded')
          elif isinstance(message, Message):
              pass
          else:
              raise TypeError('Cannot convert to specified type: %s' %
                              type(message))
  
  
  class _mboxMMDFMessage(Message):
      """Message with mbox- or MMDF-specific properties."""
  
      _type_specific_attributes = ['_from']
  
      def __init__(self, message=None):
          """Initialize an mboxMMDFMessage instance."""
          self.set_from('MAILER-DAEMON', True)
          if isinstance(message, email.message.Message):
              unixfrom = message.get_unixfrom()
              if unixfrom is not None and unixfrom.startswith('From '):
                  self.set_from(unixfrom[5:])
          Message.__init__(self, message)
  
      def get_from(self):
          """Return contents of "From " line."""
          return self._from
  
      def set_from(self, from_, time_=None):
          """Set "From " line, formatting and appending time_ if specified."""
          if time_ is not None:
              if time_ is True:
                  time_ = time.gmtime()
              from_ += ' ' + time.asctime(time_)
          self._from = from_
  
      def get_flags(self):
          """Return as a string the flags that are set."""
          return self.get('Status', '') + self.get('X-Status', '')
  
      def set_flags(self, flags):
          """Set the given flags and unset all others."""
          flags = set(flags)
          status_flags, xstatus_flags = '', ''
          for flag in ('R', 'O'):
              if flag in flags:
                  status_flags += flag
                  flags.remove(flag)
          for flag in ('D', 'F', 'A'):
              if flag in flags:
                  xstatus_flags += flag
                  flags.remove(flag)
          xstatus_flags += ''.join(sorted(flags))
          try:
              self.replace_header('Status', status_flags)
          except KeyError:
              self.add_header('Status', status_flags)
          try:
              self.replace_header('X-Status', xstatus_flags)
          except KeyError:
              self.add_header('X-Status', xstatus_flags)
  
      def add_flag(self, flag):
          """Set the given flag(s) without changing others."""
          self.set_flags(''.join(set(self.get_flags()) | set(flag)))
  
      def remove_flag(self, flag):
          """Unset the given string flag(s) without changing others."""
          if 'Status' in self or 'X-Status' in self:
              self.set_flags(''.join(set(self.get_flags()) - set(flag)))
  
      def _explain_to(self, message):
          """Copy mbox- or MMDF-specific state to message insofar as possible."""
          if isinstance(message, MaildirMessage):
              flags = set(self.get_flags())
              if 'O' in flags:
                  message.set_subdir('cur')
              if 'F' in flags:
                  message.add_flag('F')
              if 'A' in flags:
                  message.add_flag('R')
              if 'R' in flags:
                  message.add_flag('S')
              if 'D' in flags:
                  message.add_flag('T')
              del message['status']
              del message['x-status']
              maybe_date = ' '.join(self.get_from().split()[-5:])
              try:
                  message.set_date(calendar.timegm(time.strptime(maybe_date,
                                                        '%a %b %d %H:%M:%S %Y')))
              except (ValueError, OverflowError):
                  pass
          elif isinstance(message, _mboxMMDFMessage):
              message.set_flags(self.get_flags())
              message.set_from(self.get_from())
          elif isinstance(message, MHMessage):
              flags = set(self.get_flags())
              if 'R' not in flags:
                  message.add_sequence('unseen')
              if 'A' in flags:
                  message.add_sequence('replied')
              if 'F' in flags:
                  message.add_sequence('flagged')
              del message['status']
              del message['x-status']
          elif isinstance(message, BabylMessage):
              flags = set(self.get_flags())
              if 'R' not in flags:
                  message.add_label('unseen')
              if 'D' in flags:
                  message.add_label('deleted')
              if 'A' in flags:
                  message.add_label('answered')
              del message['status']
              del message['x-status']
          elif isinstance(message, Message):
              pass
          else:
              raise TypeError('Cannot convert to specified type: %s' %
                              type(message))
  
  
  class mboxMessage(_mboxMMDFMessage):
      """Message with mbox-specific properties."""
  
  
  class MHMessage(Message):
      """Message with MH-specific properties."""
  
      _type_specific_attributes = ['_sequences']
  
      def __init__(self, message=None):
          """Initialize an MHMessage instance."""
          self._sequences = []
          Message.__init__(self, message)
  
      def get_sequences(self):
          """Return a list of sequences that include the message."""
          return self._sequences[:]
  
      def set_sequences(self, sequences):
          """Set the list of sequences that include the message."""
          self._sequences = list(sequences)
  
      def add_sequence(self, sequence):
          """Add sequence to list of sequences including the message."""
          if isinstance(sequence, str):
              if not sequence in self._sequences:
                  self._sequences.append(sequence)
          else:
              raise TypeError('sequence type must be str: %s' % type(sequence))
  
      def remove_sequence(self, sequence):
          """Remove sequence from the list of sequences including the message."""
          try:
              self._sequences.remove(sequence)
          except ValueError:
              pass
  
      def _explain_to(self, message):
          """Copy MH-specific state to message insofar as possible."""
          if isinstance(message, MaildirMessage):
              sequences = set(self.get_sequences())
              if 'unseen' in sequences:
                  message.set_subdir('cur')
              else:
                  message.set_subdir('cur')
                  message.add_flag('S')
              if 'flagged' in sequences:
                  message.add_flag('F')
              if 'replied' in sequences:
                  message.add_flag('R')
          elif isinstance(message, _mboxMMDFMessage):
              sequences = set(self.get_sequences())
              if 'unseen' not in sequences:
                  message.add_flag('RO')
              else:
                  message.add_flag('O')
              if 'flagged' in sequences:
                  message.add_flag('F')
              if 'replied' in sequences:
                  message.add_flag('A')
          elif isinstance(message, MHMessage):
              for sequence in self.get_sequences():
                  message.add_sequence(sequence)
          elif isinstance(message, BabylMessage):
              sequences = set(self.get_sequences())
              if 'unseen' in sequences:
                  message.add_label('unseen')
              if 'replied' in sequences:
                  message.add_label('answered')
          elif isinstance(message, Message):
              pass
          else:
              raise TypeError('Cannot convert to specified type: %s' %
                              type(message))
  
  
  class BabylMessage(Message):
      """Message with Babyl-specific properties."""
  
      _type_specific_attributes = ['_labels', '_visible']
  
      def __init__(self, message=None):
          """Initialize an BabylMessage instance."""
          self._labels = []
          self._visible = Message()
          Message.__init__(self, message)
  
      def get_labels(self):
          """Return a list of labels on the message."""
          return self._labels[:]
  
      def set_labels(self, labels):
          """Set the list of labels on the message."""
          self._labels = list(labels)
  
      def add_label(self, label):
          """Add label to list of labels on the message."""
          if isinstance(label, str):
              if label not in self._labels:
                  self._labels.append(label)
          else:
              raise TypeError('label must be a string: %s' % type(label))
  
      def remove_label(self, label):
          """Remove label from the list of labels on the message."""
          try:
              self._labels.remove(label)
          except ValueError:
              pass
  
      def get_visible(self):
          """Return a Message representation of visible headers."""
          return Message(self._visible)
  
      def set_visible(self, visible):
          """Set the Message representation of visible headers."""
          self._visible = Message(visible)
  
      def update_visible(self):
          """Update and/or sensibly generate a set of visible headers."""
          for header in self._visible.keys():
              if header in self:
                  self._visible.replace_header(header, self[header])
              else:
                  del self._visible[header]
          for header in ('Date', 'From', 'Reply-To', 'To', 'CC', 'Subject'):
              if header in self and header not in self._visible:
                  self._visible[header] = self[header]
  
      def _explain_to(self, message):
          """Copy Babyl-specific state to message insofar as possible."""
          if isinstance(message, MaildirMessage):
              labels = set(self.get_labels())
              if 'unseen' in labels:
                  message.set_subdir('cur')
              else:
                  message.set_subdir('cur')
                  message.add_flag('S')
              if 'forwarded' in labels or 'resent' in labels:
                  message.add_flag('P')
              if 'answered' in labels:
                  message.add_flag('R')
              if 'deleted' in labels:
                  message.add_flag('T')
          elif isinstance(message, _mboxMMDFMessage):
              labels = set(self.get_labels())
              if 'unseen' not in labels:
                  message.add_flag('RO')
              else:
                  message.add_flag('O')
              if 'deleted' in labels:
                  message.add_flag('D')
              if 'answered' in labels:
                  message.add_flag('A')
          elif isinstance(message, MHMessage):
              labels = set(self.get_labels())
              if 'unseen' in labels:
                  message.add_sequence('unseen')
              if 'answered' in labels:
                  message.add_sequence('replied')
          elif isinstance(message, BabylMessage):
              message.set_visible(self.get_visible())
              for label in self.get_labels():
                  message.add_label(label)
          elif isinstance(message, Message):
              pass
          else:
              raise TypeError('Cannot convert to specified type: %s' %
                              type(message))
  
  
  class MMDFMessage(_mboxMMDFMessage):
      """Message with MMDF-specific properties."""
  
  
  class _ProxyFile:
      """A read-only wrapper of a file."""
  
      def __init__(self, f, pos=None):
          """Initialize a _ProxyFile."""
          self._file = f
          if pos is None:
              self._pos = f.tell()
          else:
              self._pos = pos
  
      def read(self, size=None):
          """Read bytes."""
          return self._read(size, self._file.read)
  
      def read1(self, size=None):
          """Read bytes."""
          return self._read(size, self._file.read1)
  
      def readline(self, size=None):
          """Read a line."""
          return self._read(size, self._file.readline)
  
      def readlines(self, sizehint=None):
          """Read multiple lines."""
          result = []
          for line in self:
              result.append(line)
              if sizehint is not None:
                  sizehint -= len(line)
                  if sizehint <= 0:
                      break
          return result
  
      def __iter__(self):
          """Iterate over lines."""
          while True:
              line = self.readline()
              if not line:
                  raise StopIteration
              yield line
  
      def tell(self):
          """Return the position."""
          return self._pos
  
      def seek(self, offset, whence=0):
          """Change position."""
          if whence == 1:
              self._file.seek(self._pos)
          self._file.seek(offset, whence)
          self._pos = self._file.tell()
  
      def close(self):
          """Close the file."""
          if hasattr(self, '_file'):
              if hasattr(self._file, 'close'):
                  self._file.close()
              del self._file
  
      def _read(self, size, read_method):
          """Read size bytes using read_method."""
          if size is None:
              size = -1
          self._file.seek(self._pos)
          result = read_method(size)
          self._pos = self._file.tell()
          return result
  
      def __enter__(self):
          """Context management protocol support."""
          return self
  
      def __exit__(self, *exc):
          self.close()
  
      def readable(self):
          return self._file.readable()
  
      def writable(self):
          return self._file.writable()
  
      def seekable(self):
          return self._file.seekable()
  
      def flush(self):
          return self._file.flush()
  
      @property
      def closed(self):
          if not hasattr(self, '_file'):
              return True
          if not hasattr(self._file, 'closed'):
              return False
          return self._file.closed
  
  
  class _PartialFile(_ProxyFile):
      """A read-only wrapper of part of a file."""
  
      def __init__(self, f, start=None, stop=None):
          """Initialize a _PartialFile."""
          _ProxyFile.__init__(self, f, start)
          self._start = start
          self._stop = stop
  
      def tell(self):
          """Return the position with respect to start."""
          return _ProxyFile.tell(self) - self._start
  
      def seek(self, offset, whence=0):
          """Change position, possibly with respect to start or stop."""
          if whence == 0:
              self._pos = self._start
              whence = 1
          elif whence == 2:
              self._pos = self._stop
              whence = 1
          _ProxyFile.seek(self, offset, whence)
  
      def _read(self, size, read_method):
          """Read size bytes using read_method, honoring start and stop."""
          remaining = self._stop - self._pos
          if remaining <= 0:
              return b''
          if size is None or size < 0 or size > remaining:
              size = remaining
          return _ProxyFile._read(self, size, read_method)
  
      def close(self):
          # do *not* close the underlying file object for partial files,
          # since it's global to the mailbox object
          if hasattr(self, '_file'):
              del self._file
  
  
  def _lock_file(f, dotlock=True):
      """Lock file f using lockf and dot locking."""
      dotlock_done = False
      try:
          if fcntl:
              try:
                  fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
              except OSError as e:
                  if e.errno in (errno.EAGAIN, errno.EACCES, errno.EROFS):
                      raise ExternalClashError('lockf: lock unavailable: %s' %
                                               f.name)
                  else:
                      raise
          if dotlock:
              try:
                  pre_lock = _create_temporary(f.name + '.lock')
                  pre_lock.close()
              except OSError as e:
                  if e.errno in (errno.EACCES, errno.EROFS):
                      return  # Without write access, just skip dotlocking.
                  else:
                      raise
              try:
                  if hasattr(os, 'link'):
                      os.link(pre_lock.name, f.name + '.lock')
                      dotlock_done = True
                      os.unlink(pre_lock.name)
                  else:
                      os.rename(pre_lock.name, f.name + '.lock')
                      dotlock_done = True
              except FileExistsError:
                  os.remove(pre_lock.name)
                  raise ExternalClashError('dot lock unavailable: %s' %
                                           f.name)
      except:
          if fcntl:
              fcntl.lockf(f, fcntl.LOCK_UN)
          if dotlock_done:
              os.remove(f.name + '.lock')
          raise
  
  def _unlock_file(f):
      """Unlock file f using lockf and dot locking."""
      if fcntl:
          fcntl.lockf(f, fcntl.LOCK_UN)
      if os.path.exists(f.name + '.lock'):
          os.remove(f.name + '.lock')
  
  def _create_carefully(path):
      """Create a file if it doesn't exist and open for reading and writing."""
      fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_RDWR, 0o666)
      try:
          return open(path, 'rb+')
      finally:
          os.close(fd)
  
  def _create_temporary(path):
      """Create a temp file based on path and open for reading and writing."""
      return _create_carefully('%s.%s.%s.%s' % (path, int(time.time()),
                                                socket.gethostname(),
                                                os.getpid()))
  
  def _sync_flush(f):
      """Ensure changes to file f are physically on disk."""
      f.flush()
      if hasattr(os, 'fsync'):
          os.fsync(f.fileno())
  
  def _sync_close(f):
      """Close file f, ensuring all changes are physically on disk."""
      _sync_flush(f)
      f.close()
  
  
  class Error(Exception):
      """Raised for module-specific errors."""
  
  class NoSuchMailboxError(Error):
      """The specified mailbox does not exist and won't be created."""
  
  class NotEmptyError(Error):
      """The specified mailbox is not empty and deletion was requested."""
  
  class ExternalClashError(Error):
      """Another process caused an action to fail."""
  
  class FormatError(Error):
      """A file appears to have an invalid format."""
  