--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/mailbox.rst Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,1701 @@
+
+:mod:`mailbox` --- Manipulate mailboxes in various formats
+==========================================================
+
+.. module:: mailbox
+ :synopsis: Manipulate mailboxes in various formats
+.. moduleauthor:: Gregory K. Johnson <gkj@gregorykjohnson.com>
+.. sectionauthor:: Gregory K. Johnson <gkj@gregorykjohnson.com>
+
+
+This module defines two classes, :class:`Mailbox` and :class:`Message`, for
+accessing and manipulating on-disk mailboxes and the messages they contain.
+:class:`Mailbox` offers a dictionary-like mapping from keys to messages.
+:class:`Message` extends the :mod:`email.Message` module's :class:`Message`
+class with format-specific state and behavior. Supported mailbox formats are
+Maildir, mbox, MH, Babyl, and MMDF.
+
+
+.. seealso::
+
+ Module :mod:`email`
+ Represent and manipulate messages.
+
+
+.. _mailbox-objects:
+
+:class:`Mailbox` objects
+------------------------
+
+
+.. class:: Mailbox
+
+ A mailbox, which may be inspected and modified.
+
+ The :class:`Mailbox` class defines an interface and is not intended to be
+ instantiated. Instead, format-specific subclasses should inherit from
+ :class:`Mailbox` and your code should instantiate a particular subclass.
+
+ The :class:`Mailbox` interface is dictionary-like, with small keys
+ corresponding to messages. Keys are issued by the :class:`Mailbox` instance
+ with which they will be used and are only meaningful to that :class:`Mailbox`
+ instance. A key continues to identify a message even if the corresponding
+ message is modified, such as by replacing it with another message.
+
+ Messages may be added to a :class:`Mailbox` instance using the set-like
+ method :meth:`add` and removed using a ``del`` statement or the set-like
+ methods :meth:`remove` and :meth:`discard`.
+
+ :class:`Mailbox` interface semantics differ from dictionary semantics in some
+ noteworthy ways. Each time a message is requested, a new representation
+ (typically a :class:`Message` instance) is generated based upon the current
+ state of the mailbox. Similarly, when a message is added to a
+ :class:`Mailbox` instance, the provided message representation's contents are
+ copied. In neither case is a reference to the message representation kept by
+ the :class:`Mailbox` instance.
+
+ The default :class:`Mailbox` iterator iterates over message representations,
+ not keys as the default dictionary iterator does. Moreover, modification of a
+ mailbox during iteration is safe and well-defined. Messages added to the
+ mailbox after an iterator is created will not be seen by the
+ iterator. Messages removed from the mailbox before the iterator yields them
+ will be silently skipped, though using a key from an iterator may result in a
+ :exc:`KeyError` exception if the corresponding message is subsequently
+ removed.
+
+ .. warning::
+
+ Be very cautious when modifying mailboxes that might be simultaneously
+ changed by some other process. The safest mailbox format to use for such
+ tasks is Maildir; try to avoid using single-file formats such as mbox for
+ concurrent writing. If you're modifying a mailbox, you *must* lock it by
+ calling the :meth:`lock` and :meth:`unlock` methods *before* reading any
+ messages in the file or making any changes by adding or deleting a
+ message. Failing to lock the mailbox runs the risk of losing messages or
+ corrupting the entire mailbox.
+
+ :class:`Mailbox` instances have the following methods:
+
+
+ .. method:: add(message)
+
+ Add *message* to the mailbox and return the key that has been assigned to
+ it.
+
+ Parameter *message* may be a :class:`Message` instance, an
+ :class:`email.Message.Message` instance, a string, or a file-like object
+ (which should be open in text mode). If *message* is an instance of the
+ appropriate format-specific :class:`Message` subclass (e.g., if it's an
+ :class:`mboxMessage` instance and this is an :class:`mbox` instance), its
+ format-specific information is used. Otherwise, reasonable defaults for
+ format-specific information are used.
+
+
+ .. method:: remove(key)
+ __delitem__(key)
+ discard(key)
+
+ Delete the message corresponding to *key* from the mailbox.
+
+ If no such message exists, a :exc:`KeyError` exception is raised if the
+ method was called as :meth:`remove` or :meth:`__delitem__` but no
+ exception is raised if the method was called as :meth:`discard`. The
+ behavior of :meth:`discard` may be preferred if the underlying mailbox
+ format supports concurrent modification by other processes.
+
+
+ .. method:: __setitem__(key, message)
+
+ Replace the message corresponding to *key* with *message*. Raise a
+ :exc:`KeyError` exception if no message already corresponds to *key*.
+
+ As with :meth:`add`, parameter *message* may be a :class:`Message`
+ instance, an :class:`email.Message.Message` instance, a string, or a
+ file-like object (which should be open in text mode). If *message* is an
+ instance of the appropriate format-specific :class:`Message` subclass
+ (e.g., if it's an :class:`mboxMessage` instance and this is an
+ :class:`mbox` instance), its format-specific information is
+ used. Otherwise, the format-specific information of the message that
+ currently corresponds to *key* is left unchanged.
+
+
+ .. method:: iterkeys()
+ keys()
+
+ Return an iterator over all keys if called as :meth:`iterkeys` or return a
+ list of keys if called as :meth:`keys`.
+
+
+ .. method:: itervalues()
+ __iter__()
+ values()
+
+ Return an iterator over representations of all messages if called as
+ :meth:`itervalues` or :meth:`__iter__` or return a list of such
+ representations if called as :meth:`values`. The messages are represented
+ as instances of the appropriate format-specific :class:`Message` subclass
+ unless a custom message factory was specified when the :class:`Mailbox`
+ instance was initialized.
+
+ .. note::
+
+ The behavior of :meth:`__iter__` is unlike that of dictionaries, which
+ iterate over keys.
+
+
+ .. method:: iteritems()
+ items()
+
+ Return an iterator over (*key*, *message*) pairs, where *key* is a key and
+ *message* is a message representation, if called as :meth:`iteritems` or
+ return a list of such pairs if called as :meth:`items`. The messages are
+ represented as instances of the appropriate format-specific
+ :class:`Message` subclass unless a custom message factory was specified
+ when the :class:`Mailbox` instance was initialized.
+
+
+ .. method:: get(key[, default=None])
+ __getitem__(key)
+
+ Return a representation of the message corresponding to *key*. If no such
+ message exists, *default* is returned if the method was called as
+ :meth:`get` and a :exc:`KeyError` exception is raised if the method was
+ called as :meth:`__getitem__`. The message is represented as an instance
+ of the appropriate format-specific :class:`Message` subclass unless a
+ custom message factory was specified when the :class:`Mailbox` instance
+ was initialized.
+
+
+ .. method:: get_message(key)
+
+ Return a representation of the message corresponding to *key* as an
+ instance of the appropriate format-specific :class:`Message` subclass, or
+ raise a :exc:`KeyError` exception if no such message exists.
+
+
+ .. method:: get_string(key)
+
+ Return a string representation of the message corresponding to *key*, or
+ raise a :exc:`KeyError` exception if no such message exists.
+
+
+ .. method:: get_file(key)
+
+ Return a file-like representation of the message corresponding to *key*,
+ or raise a :exc:`KeyError` exception if no such message exists. The
+ file-like object behaves as if open in binary mode. This file should be
+ closed once it is no longer needed.
+
+ .. note::
+
+ Unlike other representations of messages, file-like representations are
+ not necessarily independent of the :class:`Mailbox` instance that
+ created them or of the underlying mailbox. More specific documentation
+ is provided by each subclass.
+
+
+ .. method:: has_key(key)
+ __contains__(key)
+
+ Return ``True`` if *key* corresponds to a message, ``False`` otherwise.
+
+
+ .. method:: __len__()
+
+ Return a count of messages in the mailbox.
+
+
+ .. method:: clear()
+
+ Delete all messages from the mailbox.
+
+
+ .. method:: pop(key[, default])
+
+ Return a representation of the message corresponding to *key* and delete
+ the message. If no such message exists, return *default* if it was
+ supplied or else raise a :exc:`KeyError` exception. The message is
+ represented as an instance of the appropriate format-specific
+ :class:`Message` subclass unless a custom message factory was specified
+ when the :class:`Mailbox` instance was initialized.
+
+
+ .. method:: popitem()
+
+ Return an arbitrary (*key*, *message*) pair, where *key* is a key and
+ *message* is a message representation, and delete the corresponding
+ message. If the mailbox is empty, raise a :exc:`KeyError` exception. The
+ message is represented as an instance of the appropriate format-specific
+ :class:`Message` subclass unless a custom message factory was specified
+ when the :class:`Mailbox` instance was initialized.
+
+
+ .. method:: update(arg)
+
+ Parameter *arg* should be a *key*-to-*message* mapping or an iterable of
+ (*key*, *message*) pairs. Updates the mailbox so that, for each given
+ *key* and *message*, the message corresponding to *key* is set to
+ *message* as if by using :meth:`__setitem__`. As with :meth:`__setitem__`,
+ each *key* must already correspond to a message in the mailbox or else a
+ :exc:`KeyError` exception will be raised, so in general it is incorrect
+ for *arg* to be a :class:`Mailbox` instance.
+
+ .. note::
+
+ Unlike with dictionaries, keyword arguments are not supported.
+
+
+ .. method:: flush()
+
+ Write any pending changes to the filesystem. For some :class:`Mailbox`
+ subclasses, changes are always written immediately and :meth:`flush` does
+ nothing, but you should still make a habit of calling this method.
+
+
+ .. method:: lock()
+
+ Acquire an exclusive advisory lock on the mailbox so that other processes
+ know not to modify it. An :exc:`ExternalClashError` is raised if the lock
+ is not available. The particular locking mechanisms used depend upon the
+ mailbox format. You should *always* lock the mailbox before making any
+ modifications to its contents.
+
+
+ .. method:: unlock()
+
+ Release the lock on the mailbox, if any.
+
+
+ .. method:: close()
+
+ Flush the mailbox, unlock it if necessary, and close any open files. For
+ some :class:`Mailbox` subclasses, this method does nothing.
+
+
+.. _mailbox-maildir:
+
+:class:`Maildir`
+^^^^^^^^^^^^^^^^
+
+
+.. class:: Maildir(dirname[, factory=rfc822.Message[, create=True]])
+
+ A subclass of :class:`Mailbox` for mailboxes in Maildir format. Parameter
+ *factory* is a callable object that accepts a file-like message representation
+ (which behaves as if opened in binary mode) and returns a custom representation.
+ If *factory* is ``None``, :class:`MaildirMessage` is used as the default message
+ representation. If *create* is ``True``, the mailbox is created if it does not
+ exist.
+
+ It is for historical reasons that *factory* defaults to :class:`rfc822.Message`
+ and that *dirname* is named as such rather than *path*. For a :class:`Maildir`
+ instance that behaves like instances of other :class:`Mailbox` subclasses, set
+ *factory* to ``None``.
+
+ Maildir is a directory-based mailbox format invented for the qmail mail
+ transfer agent and now widely supported by other programs. Messages in a
+ Maildir mailbox are stored in separate files within a common directory
+ structure. This design allows Maildir mailboxes to be accessed and modified
+ by multiple unrelated programs without data corruption, so file locking is
+ unnecessary.
+
+ Maildir mailboxes contain three subdirectories, namely: :file:`tmp`,
+ :file:`new`, and :file:`cur`. Messages are created momentarily in the
+ :file:`tmp` subdirectory and then moved to the :file:`new` subdirectory to
+ finalize delivery. A mail user agent may subsequently move the message to the
+ :file:`cur` subdirectory and store information about the state of the message
+ in a special "info" section appended to its file name.
+
+ Folders of the style introduced by the Courier mail transfer agent are also
+ supported. Any subdirectory of the main mailbox is considered a folder if
+ ``'.'`` is the first character in its name. Folder names are represented by
+ :class:`Maildir` without the leading ``'.'``. Each folder is itself a Maildir
+ mailbox but should not contain other folders. Instead, a logical nesting is
+ indicated using ``'.'`` to delimit levels, e.g., "Archived.2005.07".
+
+ .. note::
+
+ The Maildir specification requires the use of a colon (``':'``) in certain
+ message file names. However, some operating systems do not permit this
+ character in file names, If you wish to use a Maildir-like format on such
+ an operating system, you should specify another character to use
+ instead. The exclamation point (``'!'``) is a popular choice. For
+ example::
+
+ import mailbox
+ mailbox.Maildir.colon = '!'
+
+ The :attr:`colon` attribute may also be set on a per-instance basis.
+
+ :class:`Maildir` instances have all of the methods of :class:`Mailbox` in
+ addition to the following:
+
+
+ .. method:: list_folders()
+
+ Return a list of the names of all folders.
+
+
+ .. method:: .et_folder(folder)
+
+ Return a :class:`Maildir` instance representing the folder whose name is
+ *folder*. A :exc:`NoSuchMailboxError` exception is raised if the folder
+ does not exist.
+
+
+ .. method:: add_folder(folder)
+
+ Create a folder whose name is *folder* and return a :class:`Maildir`
+ instance representing it.
+
+
+ .. method:: remove_folder(folder)
+
+ Delete the folder whose name is *folder*. If the folder contains any
+ messages, a :exc:`NotEmptyError` exception will be raised and the folder
+ will not be deleted.
+
+
+ .. method:: clean()
+
+ Delete temporary files from the mailbox that have not been accessed in the
+ last 36 hours. The Maildir specification says that mail-reading programs
+ should do this occasionally.
+
+ Some :class:`Mailbox` methods implemented by :class:`Maildir` deserve special
+ remarks:
+
+
+ .. method:: add(message)
+ __setitem__(key, message)
+ update(arg)
+
+ .. warning::
+
+ These methods generate unique file names based upon the current process
+ ID. When using multiple threads, undetected name clashes may occur and
+ cause corruption of the mailbox unless threads are coordinated to avoid
+ using these methods to manipulate the same mailbox simultaneously.
+
+
+ .. method:: flush()
+
+ All changes to Maildir mailboxes are immediately applied, so this method
+ does nothing.
+
+
+ .. method:: lock()
+ unlock()
+
+ Maildir mailboxes do not support (or require) locking, so these methods do
+ nothing.
+
+
+ .. method:: close()
+
+ :class:`Maildir` instances do not keep any open files and the underlying
+ mailboxes do not support locking, so this method does nothing.
+
+
+ .. method:: get_file(key)
+
+ Depending upon the host platform, it may not be possible to modify or
+ remove the underlying message while the returned file remains open.
+
+
+.. seealso::
+
+ `maildir man page from qmail <http://www.qmail.org/man/man5/maildir.html>`_
+ The original specification of the format.
+
+ `Using maildir format <http://cr.yp.to/proto/maildir.html>`_
+ Notes on Maildir by its inventor. Includes an updated name-creation scheme and
+ details on "info" semantics.
+
+ `maildir man page from Courier <http://www.courier-mta.org/maildir.html>`_
+ Another specification of the format. Describes a common extension for supporting
+ folders.
+
+
+.. _mailbox-mbox:
+
+:class:`mbox`
+^^^^^^^^^^^^^
+
+
+.. class:: mbox(path[, factory=None[, create=True]])
+
+ A subclass of :class:`Mailbox` for mailboxes in mbox format. Parameter *factory*
+ is a callable object that accepts a file-like message representation (which
+ behaves as if opened in binary mode) and returns a custom representation. If
+ *factory* is ``None``, :class:`mboxMessage` is used as the default message
+ representation. If *create* is ``True``, the mailbox is created if it does not
+ exist.
+
+ The mbox format is the classic format for storing mail on Unix systems. All
+ messages in an mbox mailbox are stored in a single file with the beginning of
+ each message indicated by a line whose first five characters are "From ".
+
+ Several variations of the mbox format exist to address perceived shortcomings in
+ the original. In the interest of compatibility, :class:`mbox` implements the
+ original format, which is sometimes referred to as :dfn:`mboxo`. This means that
+ the :mailheader:`Content-Length` header, if present, is ignored and that any
+ occurrences of "From " at the beginning of a line in a message body are
+ transformed to ">From " when storing the message, although occurrences of ">From
+ " are not transformed to "From " when reading the message.
+
+ Some :class:`Mailbox` methods implemented by :class:`mbox` deserve special
+ remarks:
+
+
+ .. method:: get_file(key)
+
+ Using the file after calling :meth:`flush` or :meth:`close` on the
+ :class:`mbox` instance may yield unpredictable results or raise an
+ exception.
+
+
+ .. method:: lock()
+ unlock()
+
+ Three locking mechanisms are used---dot locking and, if available, the
+ :cfunc:`flock` and :cfunc:`lockf` system calls.
+
+
+.. seealso::
+
+ `mbox man page from qmail <http://www.qmail.org/man/man5/mbox.html>`_
+ A specification of the format and its variations.
+
+ `mbox man page from tin <http://www.tin.org/bin/man.cgi?section=5&topic=mbox>`_
+ Another specification of the format, with details on locking.
+
+ `Configuring Netscape Mail on Unix: Why The Content-Length Format is Bad <http://www.jwz.org/doc/content-length.html>`_
+ An argument for using the original mbox format rather than a variation.
+
+ `"mbox" is a family of several mutually incompatible mailbox formats <http://homepages.tesco.net./~J.deBoynePollard/FGA/mail-mbox-formats.html>`_
+ A history of mbox variations.
+
+
+.. _mailbox-mh:
+
+:class:`MH`
+^^^^^^^^^^^
+
+
+.. class:: MH(path[, factory=None[, create=True]])
+
+ A subclass of :class:`Mailbox` for mailboxes in MH format. Parameter *factory*
+ is a callable object that accepts a file-like message representation (which
+ behaves as if opened in binary mode) and returns a custom representation. If
+ *factory* is ``None``, :class:`MHMessage` is used as the default message
+ representation. If *create* is ``True``, the mailbox is created if it does not
+ exist.
+
+ MH is a directory-based mailbox format invented for the MH Message Handling
+ System, a mail user agent. Each message in an MH mailbox resides in its own
+ file. An MH mailbox may contain other MH mailboxes (called :dfn:`folders`) in
+ addition to messages. Folders may be nested indefinitely. MH mailboxes also
+ support :dfn:`sequences`, which are named lists used to logically group
+ messages without moving them to sub-folders. Sequences are defined in a file
+ called :file:`.mh_sequences` in each folder.
+
+ The :class:`MH` class manipulates MH mailboxes, but it does not attempt to
+ emulate all of :program:`mh`'s behaviors. In particular, it does not modify
+ and is not affected by the :file:`context` or :file:`.mh_profile` files that
+ are used by :program:`mh` to store its state and configuration.
+
+ :class:`MH` instances have all of the methods of :class:`Mailbox` in addition
+ to the following:
+
+
+ .. method:: list_folders()
+
+ Return a list of the names of all folders.
+
+
+ .. method:: get_folder(folder)
+
+ Return an :class:`MH` instance representing the folder whose name is
+ *folder*. A :exc:`NoSuchMailboxError` exception is raised if the folder
+ does not exist.
+
+
+ .. method:: add_folder(folder)
+
+ Create a folder whose name is *folder* and return an :class:`MH` instance
+ representing it.
+
+
+ .. method:: remove_folder(folder)
+
+ Delete the folder whose name is *folder*. If the folder contains any
+ messages, a :exc:`NotEmptyError` exception will be raised and the folder
+ will not be deleted.
+
+
+ .. method:: get_sequences()
+
+ Return a dictionary of sequence names mapped to key lists. If there are no
+ sequences, the empty dictionary is returned.
+
+
+ .. method:: set_sequences(sequences)
+
+ Re-define the sequences that exist in the mailbox based upon *sequences*,
+ a dictionary of names mapped to key lists, like returned by
+ :meth:`get_sequences`.
+
+
+ .. method:: pack()
+
+ Rename messages in the mailbox as necessary to eliminate gaps in
+ numbering. Entries in the sequences list are updated correspondingly.
+
+ .. note::
+
+ Already-issued keys are invalidated by this operation and should not be
+ subsequently used.
+
+ Some :class:`Mailbox` methods implemented by :class:`MH` deserve special
+ remarks:
+
+
+ .. method:: remove(key)
+ __delitem__(key)
+ discard(key)
+
+ These methods immediately delete the message. The MH convention of marking
+ a message for deletion by prepending a comma to its name is not used.
+
+
+ .. method:: lock()
+ unlock()
+
+ Three locking mechanisms are used---dot locking and, if available, the
+ :cfunc:`flock` and :cfunc:`lockf` system calls. For MH mailboxes, locking
+ the mailbox means locking the :file:`.mh_sequences` file and, only for the
+ duration of any operations that affect them, locking individual message
+ files.
+
+
+ .. method:: get_file(key)
+
+ Depending upon the host platform, it may not be possible to remove the
+ underlying message while the returned file remains open.
+
+
+ .. method:: flush()
+
+ All changes to MH mailboxes are immediately applied, so this method does
+ nothing.
+
+
+ .. method:: close()
+
+ :class:`MH` instances do not keep any open files, so this method is
+ equivalent to :meth:`unlock`.
+
+
+.. seealso::
+
+ `nmh - Message Handling System <http://www.nongnu.org/nmh/>`_
+ Home page of :program:`nmh`, an updated version of the original :program:`mh`.
+
+ `MH & nmh: Email for Users & Programmers <http://www.ics.uci.edu/~mh/book/>`_
+ A GPL-licensed book on :program:`mh` and :program:`nmh`, with some information
+ on the mailbox format.
+
+
+.. _mailbox-babyl:
+
+:class:`Babyl`
+^^^^^^^^^^^^^^
+
+
+.. class:: Babyl(path[, factory=None[, create=True]])
+
+ A subclass of :class:`Mailbox` for mailboxes in Babyl format. Parameter
+ *factory* is a callable object that accepts a file-like message representation
+ (which behaves as if opened in binary mode) and returns a custom representation.
+ If *factory* is ``None``, :class:`BabylMessage` is used as the default message
+ representation. If *create* is ``True``, the mailbox is created if it does not
+ exist.
+
+ Babyl is a single-file mailbox format used by the Rmail mail user agent
+ included with Emacs. The beginning of a message is indicated by a line
+ containing the two characters Control-Underscore (``'\037'``) and Control-L
+ (``'\014'``). The end of a message is indicated by the start of the next
+ message or, in the case of the last message, a line containing a
+ Control-Underscore (``'\037'``) character.
+
+ Messages in a Babyl mailbox have two sets of headers, original headers and
+ so-called visible headers. Visible headers are typically a subset of the
+ original headers that have been reformatted or abridged to be more
+ attractive. Each message in a Babyl mailbox also has an accompanying list of
+ :dfn:`labels`, or short strings that record extra information about the
+ message, and a list of all user-defined labels found in the mailbox is kept
+ in the Babyl options section.
+
+ :class:`Babyl` instances have all of the methods of :class:`Mailbox` in
+ addition to the following:
+
+
+ .. method:: get_labels()
+
+ Return a list of the names of all user-defined labels used in the mailbox.
+
+ .. note::
+
+ The actual messages are inspected to determine which labels exist in
+ the mailbox rather than consulting the list of labels in the Babyl
+ options section, but the Babyl section is updated whenever the mailbox
+ is modified.
+
+ Some :class:`Mailbox` methods implemented by :class:`Babyl` deserve special
+ remarks:
+
+
+ .. method:: get_file(key)
+
+ In Babyl mailboxes, the headers of a message are not stored contiguously
+ with the body of the message. To generate a file-like representation, the
+ headers and body are copied together into a :class:`StringIO` instance
+ (from the :mod:`StringIO` module), which has an API identical to that of a
+ file. As a result, the file-like object is truly independent of the
+ underlying mailbox but does not save memory compared to a string
+ representation.
+
+
+ .. method:: lock()
+ unlock()
+
+ Three locking mechanisms are used---dot locking and, if available, the
+ :cfunc:`flock` and :cfunc:`lockf` system calls.
+
+
+.. seealso::
+
+ `Format of Version 5 Babyl Files <http://quimby.gnus.org/notes/BABYL>`_
+ A specification of the Babyl format.
+
+ `Reading Mail with Rmail <http://www.gnu.org/software/emacs/manual/html_node/emacs/Rmail.html>`_
+ The Rmail manual, with some information on Babyl semantics.
+
+
+.. _mailbox-mmdf:
+
+:class:`MMDF`
+^^^^^^^^^^^^^
+
+
+.. class:: MMDF(path[, factory=None[, create=True]])
+
+ A subclass of :class:`Mailbox` for mailboxes in MMDF format. Parameter *factory*
+ is a callable object that accepts a file-like message representation (which
+ behaves as if opened in binary mode) and returns a custom representation. If
+ *factory* is ``None``, :class:`MMDFMessage` is used as the default message
+ representation. If *create* is ``True``, the mailbox is created if it does not
+ exist.
+
+ MMDF is a single-file mailbox format invented for the Multichannel Memorandum
+ Distribution Facility, a mail transfer agent. Each message is in the same
+ form as an mbox message but is bracketed before and after by lines containing
+ four Control-A (``'\001'``) characters. As with the mbox format, the
+ beginning of each message is indicated by a line whose first five characters
+ are "From ", but additional occurrences of "From " are not transformed to
+ ">From " when storing messages because the extra message separator lines
+ prevent mistaking such occurrences for the starts of subsequent messages.
+
+ Some :class:`Mailbox` methods implemented by :class:`MMDF` deserve special
+ remarks:
+
+
+ .. method:: get_file(key)
+
+ Using the file after calling :meth:`flush` or :meth:`close` on the
+ :class:`MMDF` instance may yield unpredictable results or raise an
+ exception.
+
+
+ .. method:: lock()
+ unlock()
+
+ Three locking mechanisms are used---dot locking and, if available, the
+ :cfunc:`flock` and :cfunc:`lockf` system calls.
+
+
+.. seealso::
+
+ `mmdf man page from tin <http://www.tin.org/bin/man.cgi?section=5&topic=mmdf>`_
+ A specification of MMDF format from the documentation of tin, a newsreader.
+
+ `MMDF <http://en.wikipedia.org/wiki/MMDF>`_
+ A Wikipedia article describing the Multichannel Memorandum Distribution
+ Facility.
+
+
+.. _mailbox-message-objects:
+
+:class:`Message` objects
+------------------------
+
+
+.. class:: Message([message])
+
+ A subclass of the :mod:`email.Message` module's :class:`Message`. Subclasses of
+ :class:`mailbox.Message` add mailbox-format-specific state and behavior.
+
+ If *message* is omitted, the new instance is created in a default, empty state.
+ If *message* is an :class:`email.Message.Message` instance, its contents are
+ copied; furthermore, any format-specific information is converted insofar as
+ possible if *message* is a :class:`Message` instance. If *message* is a string
+ or a file, it should contain an :rfc:`2822`\ -compliant message, which is read
+ and parsed.
+
+ The format-specific state and behaviors offered by subclasses vary, but in
+ general it is only the properties that are not specific to a particular
+ mailbox that are supported (although presumably the properties are specific
+ to a particular mailbox format). For example, file offsets for single-file
+ mailbox formats and file names for directory-based mailbox formats are not
+ retained, because they are only applicable to the original mailbox. But state
+ such as whether a message has been read by the user or marked as important is
+ retained, because it applies to the message itself.
+
+ There is no requirement that :class:`Message` instances be used to represent
+ messages retrieved using :class:`Mailbox` instances. In some situations, the
+ time and memory required to generate :class:`Message` representations might
+ not not acceptable. For such situations, :class:`Mailbox` instances also
+ offer string and file-like representations, and a custom message factory may
+ be specified when a :class:`Mailbox` instance is initialized.
+
+
+.. _mailbox-maildirmessage:
+
+:class:`MaildirMessage`
+^^^^^^^^^^^^^^^^^^^^^^^
+
+
+.. class:: MaildirMessage([message])
+
+ A message with Maildir-specific behaviors. Parameter *message* has the same
+ meaning as with the :class:`Message` constructor.
+
+ Typically, a mail user agent application moves all of the messages in the
+ :file:`new` subdirectory to the :file:`cur` subdirectory after the first time
+ the user opens and closes the mailbox, recording that the messages are old
+ whether or not they've actually been read. Each message in :file:`cur` has an
+ "info" section added to its file name to store information about its state.
+ (Some mail readers may also add an "info" section to messages in
+ :file:`new`.) The "info" section may take one of two forms: it may contain
+ "2," followed by a list of standardized flags (e.g., "2,FR") or it may
+ contain "1," followed by so-called experimental information. Standard flags
+ for Maildir messages are as follows:
+
+ +------+---------+--------------------------------+
+ | Flag | Meaning | Explanation |
+ +======+=========+================================+
+ | D | Draft | Under composition |
+ +------+---------+--------------------------------+
+ | F | Flagged | Marked as important |
+ +------+---------+--------------------------------+
+ | P | Passed | Forwarded, resent, or bounced |
+ +------+---------+--------------------------------+
+ | R | Replied | Replied to |
+ +------+---------+--------------------------------+
+ | S | Seen | Read |
+ +------+---------+--------------------------------+
+ | T | Trashed | Marked for subsequent deletion |
+ +------+---------+--------------------------------+
+
+ :class:`MaildirMessage` instances offer the following methods:
+
+
+ .. method:: get_subdir()
+
+ Return either "new" (if the message should be stored in the :file:`new`
+ subdirectory) or "cur" (if the message should be stored in the :file:`cur`
+ subdirectory).
+
+ .. note::
+
+ A message is typically moved from :file:`new` to :file:`cur` after its
+ mailbox has been accessed, whether or not the message is has been
+ read. A message ``msg`` has been read if ``"S" in msg.get_flags()`` is
+ ``True``.
+
+
+ .. method:: set_subdir(subdir)
+
+ Set the subdirectory the message should be stored in. Parameter *subdir*
+ must be either "new" or "cur".
+
+
+ .. method:: get_flags()
+
+ Return a string specifying the flags that are currently set. If the
+ message complies with the standard Maildir format, the result is the
+ concatenation in alphabetical order of zero or one occurrence of each of
+ ``'D'``, ``'F'``, ``'P'``, ``'R'``, ``'S'``, and ``'T'``. The empty string
+ is returned if no flags are set or if "info" contains experimental
+ semantics.
+
+
+ .. method:: set_flags(flags)
+
+ Set the flags specified by *flags* and unset all others.
+
+
+ .. method:: add_flag(flag)
+
+ Set the flag(s) specified by *flag* without changing other flags. To add
+ more than one flag at a time, *flag* may be a string of more than one
+ character. The current "info" is overwritten whether or not it contains
+ experimental information rather than flags.
+
+
+ .. method:: remove_flag(flag)
+
+ Unset the flag(s) specified by *flag* without changing other flags. To
+ remove more than one flag at a time, *flag* maybe a string of more than
+ one character. If "info" contains experimental information rather than
+ flags, the current "info" is not modified.
+
+
+ .. method:: get_date()
+
+ Return the delivery date of the message as a floating-point number
+ representing seconds since the epoch.
+
+
+ .. method:: set_date(date)
+
+ Set the delivery date of the message to *date*, a floating-point number
+ representing seconds since the epoch.
+
+
+ .. method:: get_info()
+
+ Return a string containing the "info" for a message. This is useful for
+ accessing and modifying "info" that is experimental (i.e., not a list of
+ flags).
+
+
+ .. method:: set_info(info)
+
+ Set "info" to *info*, which should be a string.
+
+When a :class:`MaildirMessage` instance is created based upon an
+:class:`mboxMessage` or :class:`MMDFMessage` instance, the :mailheader:`Status`
+and :mailheader:`X-Status` headers are omitted and the following conversions
+take place:
+
++--------------------+----------------------------------------------+
+| Resulting state | :class:`mboxMessage` or :class:`MMDFMessage` |
+| | state |
++====================+==============================================+
+| "cur" subdirectory | O flag |
++--------------------+----------------------------------------------+
+| F flag | F flag |
++--------------------+----------------------------------------------+
+| R flag | A flag |
++--------------------+----------------------------------------------+
+| S flag | R flag |
++--------------------+----------------------------------------------+
+| T flag | D flag |
++--------------------+----------------------------------------------+
+
+When a :class:`MaildirMessage` instance is created based upon an
+:class:`MHMessage` instance, the following conversions take place:
+
++-------------------------------+--------------------------+
+| Resulting state | :class:`MHMessage` state |
++===============================+==========================+
+| "cur" subdirectory | "unseen" sequence |
++-------------------------------+--------------------------+
+| "cur" subdirectory and S flag | no "unseen" sequence |
++-------------------------------+--------------------------+
+| F flag | "flagged" sequence |
++-------------------------------+--------------------------+
+| R flag | "replied" sequence |
++-------------------------------+--------------------------+
+
+When a :class:`MaildirMessage` instance is created based upon a
+:class:`BabylMessage` instance, the following conversions take place:
+
++-------------------------------+-------------------------------+
+| Resulting state | :class:`BabylMessage` state |
++===============================+===============================+
+| "cur" subdirectory | "unseen" label |
++-------------------------------+-------------------------------+
+| "cur" subdirectory and S flag | no "unseen" label |
++-------------------------------+-------------------------------+
+| P flag | "forwarded" or "resent" label |
++-------------------------------+-------------------------------+
+| R flag | "answered" label |
++-------------------------------+-------------------------------+
+| T flag | "deleted" label |
++-------------------------------+-------------------------------+
+
+
+.. _mailbox-mboxmessage:
+
+:class:`mboxMessage`
+^^^^^^^^^^^^^^^^^^^^
+
+
+.. class:: mboxMessage([message])
+
+ A message with mbox-specific behaviors. Parameter *message* has the same meaning
+ as with the :class:`Message` constructor.
+
+ Messages in an mbox mailbox are stored together in a single file. The
+ sender's envelope address and the time of delivery are typically stored in a
+ line beginning with "From " that is used to indicate the start of a message,
+ though there is considerable variation in the exact format of this data among
+ mbox implementations. Flags that indicate the state of the message, such as
+ whether it has been read or marked as important, are typically stored in
+ :mailheader:`Status` and :mailheader:`X-Status` headers.
+
+ Conventional flags for mbox messages are as follows:
+
+ +------+----------+--------------------------------+
+ | Flag | Meaning | Explanation |
+ +======+==========+================================+
+ | R | Read | Read |
+ +------+----------+--------------------------------+
+ | O | Old | Previously detected by MUA |
+ +------+----------+--------------------------------+
+ | D | Deleted | Marked for subsequent deletion |
+ +------+----------+--------------------------------+
+ | F | Flagged | Marked as important |
+ +------+----------+--------------------------------+
+ | A | Answered | Replied to |
+ +------+----------+--------------------------------+
+
+ The "R" and "O" flags are stored in the :mailheader:`Status` header, and the
+ "D", "F", and "A" flags are stored in the :mailheader:`X-Status` header. The
+ flags and headers typically appear in the order mentioned.
+
+ :class:`mboxMessage` instances offer the following methods:
+
+
+ .. method:: get_from()
+
+ Return a string representing the "From " line that marks the start of the
+ message in an mbox mailbox. The leading "From " and the trailing newline
+ are excluded.
+
+
+ .. method:: set_from(from_[, time_=None])
+
+ Set the "From " line to *from_*, which should be specified without a
+ leading "From " or trailing newline. For convenience, *time_* may be
+ specified and will be formatted appropriately and appended to *from_*. If
+ *time_* is specified, it should be a :class:`struct_time` instance, a
+ tuple suitable for passing to :meth:`time.strftime`, or ``True`` (to use
+ :meth:`time.gmtime`).
+
+
+ .. method:: get_flags()
+
+ Return a string specifying the flags that are currently set. If the
+ message complies with the conventional format, the result is the
+ concatenation in the following order of zero or one occurrence of each of
+ ``'R'``, ``'O'``, ``'D'``, ``'F'``, and ``'A'``.
+
+
+ .. method:: set_flags(flags)
+
+ Set the flags specified by *flags* and unset all others. Parameter *flags*
+ should be the concatenation in any order of zero or more occurrences of
+ each of ``'R'``, ``'O'``, ``'D'``, ``'F'``, and ``'A'``.
+
+
+ .. method:: add_flag(flag)
+
+ Set the flag(s) specified by *flag* without changing other flags. To add
+ more than one flag at a time, *flag* may be a string of more than one
+ character.
+
+
+ .. method:: remove_flag(flag)
+
+ Unset the flag(s) specified by *flag* without changing other flags. To
+ remove more than one flag at a time, *flag* maybe a string of more than
+ one character.
+
+When an :class:`mboxMessage` instance is created based upon a
+:class:`MaildirMessage` instance, a "From " line is generated based upon the
+:class:`MaildirMessage` instance's delivery date, and the following conversions
+take place:
+
++-----------------+-------------------------------+
+| Resulting state | :class:`MaildirMessage` state |
++=================+===============================+
+| R flag | S flag |
++-----------------+-------------------------------+
+| O flag | "cur" subdirectory |
++-----------------+-------------------------------+
+| D flag | T flag |
++-----------------+-------------------------------+
+| F flag | F flag |
++-----------------+-------------------------------+
+| A flag | R flag |
++-----------------+-------------------------------+
+
+When an :class:`mboxMessage` instance is created based upon an
+:class:`MHMessage` instance, the following conversions take place:
+
++-------------------+--------------------------+
+| Resulting state | :class:`MHMessage` state |
++===================+==========================+
+| R flag and O flag | no "unseen" sequence |
++-------------------+--------------------------+
+| O flag | "unseen" sequence |
++-------------------+--------------------------+
+| F flag | "flagged" sequence |
++-------------------+--------------------------+
+| A flag | "replied" sequence |
++-------------------+--------------------------+
+
+When an :class:`mboxMessage` instance is created based upon a
+:class:`BabylMessage` instance, the following conversions take place:
+
++-------------------+-----------------------------+
+| Resulting state | :class:`BabylMessage` state |
++===================+=============================+
+| R flag and O flag | no "unseen" label |
++-------------------+-----------------------------+
+| O flag | "unseen" label |
++-------------------+-----------------------------+
+| D flag | "deleted" label |
++-------------------+-----------------------------+
+| A flag | "answered" label |
++-------------------+-----------------------------+
+
+When a :class:`Message` instance is created based upon an :class:`MMDFMessage`
+instance, the "From " line is copied and all flags directly correspond:
+
++-----------------+----------------------------+
+| Resulting state | :class:`MMDFMessage` state |
++=================+============================+
+| R flag | R flag |
++-----------------+----------------------------+
+| O flag | O flag |
++-----------------+----------------------------+
+| D flag | D flag |
++-----------------+----------------------------+
+| F flag | F flag |
++-----------------+----------------------------+
+| A flag | A flag |
++-----------------+----------------------------+
+
+
+.. _mailbox-mhmessage:
+
+:class:`MHMessage`
+^^^^^^^^^^^^^^^^^^
+
+
+.. class:: MHMessage([message])
+
+ A message with MH-specific behaviors. Parameter *message* has the same meaning
+ as with the :class:`Message` constructor.
+
+ MH messages do not support marks or flags in the traditional sense, but they
+ do support sequences, which are logical groupings of arbitrary messages. Some
+ mail reading programs (although not the standard :program:`mh` and
+ :program:`nmh`) use sequences in much the same way flags are used with other
+ formats, as follows:
+
+ +----------+------------------------------------------+
+ | Sequence | Explanation |
+ +==========+==========================================+
+ | unseen | Not read, but previously detected by MUA |
+ +----------+------------------------------------------+
+ | replied | Replied to |
+ +----------+------------------------------------------+
+ | flagged | Marked as important |
+ +----------+------------------------------------------+
+
+ :class:`MHMessage` instances offer the following methods:
+
+
+ .. method:: get_sequences()
+
+ Return a list of the names of sequences that include this message.
+
+
+ .. method:: set_sequences(sequences)
+
+ Set the list of sequences that include this message.
+
+
+ .. method:: add_sequence(sequence)
+
+ Add *sequence* to the list of sequences that include this message.
+
+
+ .. method:: remove_sequence(sequence)
+
+ Remove *sequence* from the list of sequences that include this message.
+
+When an :class:`MHMessage` instance is created based upon a
+:class:`MaildirMessage` instance, the following conversions take place:
+
++--------------------+-------------------------------+
+| Resulting state | :class:`MaildirMessage` state |
++====================+===============================+
+| "unseen" sequence | no S flag |
++--------------------+-------------------------------+
+| "replied" sequence | R flag |
++--------------------+-------------------------------+
+| "flagged" sequence | F flag |
++--------------------+-------------------------------+
+
+When an :class:`MHMessage` instance is created based upon an
+:class:`mboxMessage` or :class:`MMDFMessage` instance, the :mailheader:`Status`
+and :mailheader:`X-Status` headers are omitted and the following conversions
+take place:
+
++--------------------+----------------------------------------------+
+| Resulting state | :class:`mboxMessage` or :class:`MMDFMessage` |
+| | state |
++====================+==============================================+
+| "unseen" sequence | no R flag |
++--------------------+----------------------------------------------+
+| "replied" sequence | A flag |
++--------------------+----------------------------------------------+
+| "flagged" sequence | F flag |
++--------------------+----------------------------------------------+
+
+When an :class:`MHMessage` instance is created based upon a
+:class:`BabylMessage` instance, the following conversions take place:
+
++--------------------+-----------------------------+
+| Resulting state | :class:`BabylMessage` state |
++====================+=============================+
+| "unseen" sequence | "unseen" label |
++--------------------+-----------------------------+
+| "replied" sequence | "answered" label |
++--------------------+-----------------------------+
+
+
+.. _mailbox-babylmessage:
+
+:class:`BabylMessage`
+^^^^^^^^^^^^^^^^^^^^^
+
+
+.. class:: BabylMessage([message])
+
+ A message with Babyl-specific behaviors. Parameter *message* has the same
+ meaning as with the :class:`Message` constructor.
+
+ Certain message labels, called :dfn:`attributes`, are defined by convention
+ to have special meanings. The attributes are as follows:
+
+ +-----------+------------------------------------------+
+ | Label | Explanation |
+ +===========+==========================================+
+ | unseen | Not read, but previously detected by MUA |
+ +-----------+------------------------------------------+
+ | deleted | Marked for subsequent deletion |
+ +-----------+------------------------------------------+
+ | filed | Copied to another file or mailbox |
+ +-----------+------------------------------------------+
+ | answered | Replied to |
+ +-----------+------------------------------------------+
+ | forwarded | Forwarded |
+ +-----------+------------------------------------------+
+ | edited | Modified by the user |
+ +-----------+------------------------------------------+
+ | resent | Resent |
+ +-----------+------------------------------------------+
+
+ By default, Rmail displays only visible headers. The :class:`BabylMessage`
+ class, though, uses the original headers because they are more
+ complete. Visible headers may be accessed explicitly if desired.
+
+ :class:`BabylMessage` instances offer the following methods:
+
+
+ .. method:: get_labels()
+
+ Return a list of labels on the message.
+
+
+ .. method:: set_labels(labels)
+
+ Set the list of labels on the message to *labels*.
+
+
+ .. method:: add_label(label)
+
+ Add *label* to the list of labels on the message.
+
+
+ .. method:: remove_label(label)
+
+ Remove *label* from the list of labels on the message.
+
+
+ .. method:: get_visible()
+
+ Return an :class:`Message` instance whose headers are the message's
+ visible headers and whose body is empty.
+
+
+ .. method:: set_visible(visible)
+
+ Set the message's visible headers to be the same as the headers in
+ *message*. Parameter *visible* should be a :class:`Message` instance, an
+ :class:`email.Message.Message` instance, a string, or a file-like object
+ (which should be open in text mode).
+
+
+ .. method:: update_visible()
+
+ When a :class:`BabylMessage` instance's original headers are modified, the
+ visible headers are not automatically modified to correspond. This method
+ updates the visible headers as follows: each visible header with a
+ corresponding original header is set to the value of the original header,
+ each visible header without a corresponding original header is removed,
+ and any of :mailheader:`Date`, :mailheader:`From`, :mailheader:`Reply-To`,
+ :mailheader:`To`, :mailheader:`CC`, and :mailheader:`Subject` that are
+ present in the original headers but not the visible headers are added to
+ the visible headers.
+
+When a :class:`BabylMessage` instance is created based upon a
+:class:`MaildirMessage` instance, the following conversions take place:
+
++-------------------+-------------------------------+
+| Resulting state | :class:`MaildirMessage` state |
++===================+===============================+
+| "unseen" label | no S flag |
++-------------------+-------------------------------+
+| "deleted" label | T flag |
++-------------------+-------------------------------+
+| "answered" label | R flag |
++-------------------+-------------------------------+
+| "forwarded" label | P flag |
++-------------------+-------------------------------+
+
+When a :class:`BabylMessage` instance is created based upon an
+:class:`mboxMessage` or :class:`MMDFMessage` instance, the :mailheader:`Status`
+and :mailheader:`X-Status` headers are omitted and the following conversions
+take place:
+
++------------------+----------------------------------------------+
+| Resulting state | :class:`mboxMessage` or :class:`MMDFMessage` |
+| | state |
++==================+==============================================+
+| "unseen" label | no R flag |
++------------------+----------------------------------------------+
+| "deleted" label | D flag |
++------------------+----------------------------------------------+
+| "answered" label | A flag |
++------------------+----------------------------------------------+
+
+When a :class:`BabylMessage` instance is created based upon an
+:class:`MHMessage` instance, the following conversions take place:
+
++------------------+--------------------------+
+| Resulting state | :class:`MHMessage` state |
++==================+==========================+
+| "unseen" label | "unseen" sequence |
++------------------+--------------------------+
+| "answered" label | "replied" sequence |
++------------------+--------------------------+
+
+
+.. _mailbox-mmdfmessage:
+
+:class:`MMDFMessage`
+^^^^^^^^^^^^^^^^^^^^
+
+
+.. class:: MMDFMessage([message])
+
+ A message with MMDF-specific behaviors. Parameter *message* has the same meaning
+ as with the :class:`Message` constructor.
+
+ As with message in an mbox mailbox, MMDF messages are stored with the
+ sender's address and the delivery date in an initial line beginning with
+ "From ". Likewise, flags that indicate the state of the message are
+ typically stored in :mailheader:`Status` and :mailheader:`X-Status` headers.
+
+ Conventional flags for MMDF messages are identical to those of mbox message
+ and are as follows:
+
+ +------+----------+--------------------------------+
+ | Flag | Meaning | Explanation |
+ +======+==========+================================+
+ | R | Read | Read |
+ +------+----------+--------------------------------+
+ | O | Old | Previously detected by MUA |
+ +------+----------+--------------------------------+
+ | D | Deleted | Marked for subsequent deletion |
+ +------+----------+--------------------------------+
+ | F | Flagged | Marked as important |
+ +------+----------+--------------------------------+
+ | A | Answered | Replied to |
+ +------+----------+--------------------------------+
+
+ The "R" and "O" flags are stored in the :mailheader:`Status` header, and the
+ "D", "F", and "A" flags are stored in the :mailheader:`X-Status` header. The
+ flags and headers typically appear in the order mentioned.
+
+ :class:`MMDFMessage` instances offer the following methods, which are
+ identical to those offered by :class:`mboxMessage`:
+
+
+ .. method:: get_from()
+
+ Return a string representing the "From " line that marks the start of the
+ message in an mbox mailbox. The leading "From " and the trailing newline
+ are excluded.
+
+
+ .. method:: set_from(from_[, time_=None])
+
+ Set the "From " line to *from_*, which should be specified without a
+ leading "From " or trailing newline. For convenience, *time_* may be
+ specified and will be formatted appropriately and appended to *from_*. If
+ *time_* is specified, it should be a :class:`struct_time` instance, a
+ tuple suitable for passing to :meth:`time.strftime`, or ``True`` (to use
+ :meth:`time.gmtime`).
+
+
+ .. method:: get_flags()
+
+ Return a string specifying the flags that are currently set. If the
+ message complies with the conventional format, the result is the
+ concatenation in the following order of zero or one occurrence of each of
+ ``'R'``, ``'O'``, ``'D'``, ``'F'``, and ``'A'``.
+
+
+ .. method:: set_flags(flags)
+
+ Set the flags specified by *flags* and unset all others. Parameter *flags*
+ should be the concatenation in any order of zero or more occurrences of
+ each of ``'R'``, ``'O'``, ``'D'``, ``'F'``, and ``'A'``.
+
+
+ .. method:: add_flag(flag)
+
+ Set the flag(s) specified by *flag* without changing other flags. To add
+ more than one flag at a time, *flag* may be a string of more than one
+ character.
+
+
+ .. method:: remove_flag(flag)
+
+ Unset the flag(s) specified by *flag* without changing other flags. To
+ remove more than one flag at a time, *flag* maybe a string of more than
+ one character.
+
+When an :class:`MMDFMessage` instance is created based upon a
+:class:`MaildirMessage` instance, a "From " line is generated based upon the
+:class:`MaildirMessage` instance's delivery date, and the following conversions
+take place:
+
++-----------------+-------------------------------+
+| Resulting state | :class:`MaildirMessage` state |
++=================+===============================+
+| R flag | S flag |
++-----------------+-------------------------------+
+| O flag | "cur" subdirectory |
++-----------------+-------------------------------+
+| D flag | T flag |
++-----------------+-------------------------------+
+| F flag | F flag |
++-----------------+-------------------------------+
+| A flag | R flag |
++-----------------+-------------------------------+
+
+When an :class:`MMDFMessage` instance is created based upon an
+:class:`MHMessage` instance, the following conversions take place:
+
++-------------------+--------------------------+
+| Resulting state | :class:`MHMessage` state |
++===================+==========================+
+| R flag and O flag | no "unseen" sequence |
++-------------------+--------------------------+
+| O flag | "unseen" sequence |
++-------------------+--------------------------+
+| F flag | "flagged" sequence |
++-------------------+--------------------------+
+| A flag | "replied" sequence |
++-------------------+--------------------------+
+
+When an :class:`MMDFMessage` instance is created based upon a
+:class:`BabylMessage` instance, the following conversions take place:
+
++-------------------+-----------------------------+
+| Resulting state | :class:`BabylMessage` state |
++===================+=============================+
+| R flag and O flag | no "unseen" label |
++-------------------+-----------------------------+
+| O flag | "unseen" label |
++-------------------+-----------------------------+
+| D flag | "deleted" label |
++-------------------+-----------------------------+
+| A flag | "answered" label |
++-------------------+-----------------------------+
+
+When an :class:`MMDFMessage` instance is created based upon an
+:class:`mboxMessage` instance, the "From " line is copied and all flags directly
+correspond:
+
++-----------------+----------------------------+
+| Resulting state | :class:`mboxMessage` state |
++=================+============================+
+| R flag | R flag |
++-----------------+----------------------------+
+| O flag | O flag |
++-----------------+----------------------------+
+| D flag | D flag |
++-----------------+----------------------------+
+| F flag | F flag |
++-----------------+----------------------------+
+| A flag | A flag |
++-----------------+----------------------------+
+
+
+Exceptions
+----------
+
+The following exception classes are defined in the :mod:`mailbox` module:
+
+
+.. exception:: Error()
+
+ The based class for all other module-specific exceptions.
+
+
+.. exception:: NoSuchMailboxError()
+
+ Raised when a mailbox is expected but is not found, such as when instantiating a
+ :class:`Mailbox` subclass with a path that does not exist (and with the *create*
+ parameter set to ``False``), or when opening a folder that does not exist.
+
+
+.. exception:: NotEmptyError()
+
+ Raised when a mailbox is not empty but is expected to be, such as when deleting
+ a folder that contains messages.
+
+
+.. exception:: ExternalClashError()
+
+ Raised when some mailbox-related condition beyond the control of the program
+ causes it to be unable to proceed, such as when failing to acquire a lock that
+ another program already holds a lock, or when a uniquely-generated file name
+ already exists.
+
+
+.. exception:: FormatError()
+
+ Raised when the data in a file cannot be parsed, such as when an :class:`MH`
+ instance attempts to read a corrupted :file:`.mh_sequences` file.
+
+
+.. _mailbox-deprecated:
+
+Deprecated classes and methods
+------------------------------
+
+.. deprecated:: 2.6
+
+Older versions of the :mod:`mailbox` module do not support modification of
+mailboxes, such as adding or removing message, and do not provide classes to
+represent format-specific message properties. For backward compatibility, the
+older mailbox classes are still available, but the newer classes should be used
+in preference to them. The old classes will be removed in Python 3.0.
+
+Older mailbox objects support only iteration and provide a single public method:
+
+
+.. method:: oldmailbox.next()
+
+ Return the next message in the mailbox, created with the optional *factory*
+ argument passed into the mailbox object's constructor. By default this is an
+ :class:`rfc822.Message` object (see the :mod:`rfc822` module). Depending on the
+ mailbox implementation the *fp* attribute of this object may be a true file
+ object or a class instance simulating a file object, taking care of things like
+ message boundaries if multiple mail messages are contained in a single file,
+ etc. If no more messages are available, this method returns ``None``.
+
+Most of the older mailbox classes have names that differ from the current
+mailbox class names, except for :class:`Maildir`. For this reason, the new
+:class:`Maildir` class defines a :meth:`next` method and its constructor differs
+slightly from those of the other new mailbox classes.
+
+The older mailbox classes whose names are not the same as their newer
+counterparts are as follows:
+
+
+.. class:: UnixMailbox(fp[, factory])
+
+ Access to a classic Unix-style mailbox, where all messages are contained in a
+ single file and separated by ``From`` (a.k.a. ``From_``) lines. The file object
+ *fp* points to the mailbox file. The optional *factory* parameter is a callable
+ that should create new message objects. *factory* is called with one argument,
+ *fp* by the :meth:`next` method of the mailbox object. The default is the
+ :class:`rfc822.Message` class (see the :mod:`rfc822` module -- and the note
+ below).
+
+ .. note::
+
+ For reasons of this module's internal implementation, you will probably want to
+ open the *fp* object in binary mode. This is especially important on Windows.
+
+ For maximum portability, messages in a Unix-style mailbox are separated by any
+ line that begins exactly with the string ``'From '`` (note the trailing space)
+ if preceded by exactly two newlines. Because of the wide-range of variations in
+ practice, nothing else on the ``From_`` line should be considered. However, the
+ current implementation doesn't check for the leading two newlines. This is
+ usually fine for most applications.
+
+ The :class:`UnixMailbox` class implements a more strict version of ``From_``
+ line checking, using a regular expression that usually correctly matched
+ ``From_`` delimiters. It considers delimiter line to be separated by ``From
+ name time`` lines. For maximum portability, use the
+ :class:`PortableUnixMailbox` class instead. This class is identical to
+ :class:`UnixMailbox` except that individual messages are separated by only
+ ``From`` lines.
+
+
+.. class:: PortableUnixMailbox(fp[, factory])
+
+ A less-strict version of :class:`UnixMailbox`, which considers only the ``From``
+ at the beginning of the line separating messages. The "*name* *time*" portion
+ of the From line is ignored, to protect against some variations that are
+ observed in practice. This works since lines in the message which begin with
+ ``'From '`` are quoted by mail handling software at delivery-time.
+
+
+.. class:: MmdfMailbox(fp[, factory])
+
+ Access an MMDF-style mailbox, where all messages are contained in a single file
+ and separated by lines consisting of 4 control-A characters. The file object
+ *fp* points to the mailbox file. Optional *factory* is as with the
+ :class:`UnixMailbox` class.
+
+
+.. class:: MHMailbox(dirname[, factory])
+
+ Access an MH mailbox, a directory with each message in a separate file with a
+ numeric name. The name of the mailbox directory is passed in *dirname*.
+ *factory* is as with the :class:`UnixMailbox` class.
+
+
+.. class:: BabylMailbox(fp[, factory])
+
+ Access a Babyl mailbox, which is similar to an MMDF mailbox. In Babyl format,
+ each message has two sets of headers, the *original* headers and the *visible*
+ headers. The original headers appear before a line containing only ``'*** EOOH
+ ***'`` (End-Of-Original-Headers) and the visible headers appear after the
+ ``EOOH`` line. Babyl-compliant mail readers will show you only the visible
+ headers, and :class:`BabylMailbox` objects will return messages containing only
+ the visible headers. You'll have to do your own parsing of the mailbox file to
+ get at the original headers. Mail messages start with the EOOH line and end
+ with a line containing only ``'\037\014'``. *factory* is as with the
+ :class:`UnixMailbox` class.
+
+If you wish to use the older mailbox classes with the :mod:`email` module rather
+than the deprecated :mod:`rfc822` module, you can do so as follows::
+
+ import email
+ import email.Errors
+ import mailbox
+
+ def msgfactory(fp):
+ try:
+ return email.message_from_file(fp)
+ except email.Errors.MessageParseError:
+ # Don't return None since that will
+ # stop the mailbox iterator
+ return ''
+
+ mbox = mailbox.UnixMailbox(fp, msgfactory)
+
+Alternatively, if you know your mailbox contains only well-formed MIME messages,
+you can simplify this to::
+
+ import email
+ import mailbox
+
+ mbox = mailbox.UnixMailbox(fp, email.message_from_file)
+
+
+.. _mailbox-examples:
+
+Examples
+--------
+
+A simple example of printing the subjects of all messages in a mailbox that seem
+interesting::
+
+ import mailbox
+ for message in mailbox.mbox('~/mbox'):
+ subject = message['subject'] # Could possibly be None.
+ if subject and 'python' in subject.lower():
+ print subject
+
+To copy all mail from a Babyl mailbox to an MH mailbox, converting all of the
+format-specific information that can be converted::
+
+ import mailbox
+ destination = mailbox.MH('~/Mail')
+ destination.lock()
+ for message in mailbox.Babyl('~/RMAIL'):
+ destination.add(mailbox.MHMessage(message))
+ destination.flush()
+ destination.unlock()
+
+This example sorts mail from several mailing lists into different mailboxes,
+being careful to avoid mail corruption due to concurrent modification by other
+programs, mail loss due to interruption of the program, or premature termination
+due to malformed messages in the mailbox::
+
+ import mailbox
+ import email.Errors
+
+ list_names = ('python-list', 'python-dev', 'python-bugs')
+
+ boxes = dict((name, mailbox.mbox('~/email/%s' % name)) for name in list_names)
+ inbox = mailbox.Maildir('~/Maildir', factory=None)
+
+ for key in inbox.iterkeys():
+ try:
+ message = inbox[key]
+ except email.Errors.MessageParseError:
+ continue # The message is malformed. Just leave it.
+
+ for name in list_names:
+ list_id = message['list-id']
+ if list_id and name in list_id:
+ # Get mailbox to use
+ box = boxes[name]
+
+ # Write copy to disk before removing original.
+ # If there's a crash, you might duplicate a message, but
+ # that's better than losing a message completely.
+ box.lock()
+ box.add(message)
+ box.flush()
+ box.unlock()
+
+ # Remove original message
+ inbox.lock()
+ inbox.discard(key)
+ inbox.flush()
+ inbox.unlock()
+ break # Found destination, so stop looking.
+
+ for box in boxes.itervalues():
+ box.close()
+