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cpython/Doc/library/mailbox.rst
Martin Panter 7462b64911 Issue #25523: Correct "a" article to "an" article 
This changes the main documentation, doc strings, source code comments, and a
couple error messages in the test suite. In some cases the word was removed
or edited some other way to fix the grammar.
2015-11-02 03:37:02 +00:00

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: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:`~email.message.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, a byte string, or a
file-like object (which should be open in binary 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.
.. versionchanged:: 3.2
Support for binary input was added.
.. 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, a byte
string, or a file-like object (which should be open in binary 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_bytes(key)
Return a byte representation of the message corresponding to *key*, or
raise a :exc:`KeyError` exception if no such message exists.
.. versionadded:: 3.2
.. 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. The
message is processed through :class:`email.message.Message` to
convert it to a 7bit clean representation.
.. 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.
.. versionchanged:: 3.2
The file object really is a binary file; previously it was incorrectly
returned in text mode. Also, the file-like object now supports the
context management protocol: you can use a :keyword:`with` statement to
automatically close it.
.. 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:: __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=None)
Return a representation of the message corresponding to *key* and delete
the message. If no such message exists, return *default*. 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=None, 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 *dirname* is named as such rather than *path*.
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:: get_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
:c:func:`flock` and :c:func:`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://homepage.ntlworld.com/jonathan.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
:c:func:`flock` and :c:func:`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://rand-mh.sourceforge.net/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 an :class:`io.BytesIO` instance,
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
:c:func:`flock` and :c:func:`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
:c:func:`flock` and :c:func:`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=None)
A subclass of the :mod:`email.message` module's
:class:`~email.message.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,
a byte string,
or a file, it should contain an :rfc:`2822`\ -compliant message, which is read
and parsed. Files should be open in binary mode, but text mode files
are accepted for backward compatibility.
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 be 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=None)
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=None)
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:`time.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=None)
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=None)
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=None)
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:`time.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-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 = {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()
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