cpython/Doc/lib/email.tex

% Copyright (C) 2001-2004 Python Software Foundation
% Author: barry@python.org (Barry Warsaw)

\section{\module{email} ---
	 An email and MIME handling package}

\declaremodule{standard}{email}
\modulesynopsis{Package supporting the parsing, manipulating, and
    generating email messages, including MIME documents.}
\moduleauthor{Barry A. Warsaw}{barry@python.org}
\sectionauthor{Barry A. Warsaw}{barry@python.org}

\versionadded{2.2}

The \module{email} package is a library for managing email messages,
including MIME and other \rfc{2822}-based message documents.  It
subsumes most of the functionality in several older standard modules
such as \refmodule{rfc822}, \refmodule{mimetools},
\refmodule{multifile}, and other non-standard packages such as
\module{mimecntl}.  It is specifically \emph{not} designed to do any
sending of email messages to SMTP (\rfc{2821}) servers; that is the
function of the \refmodule{smtplib} module.  The \module{email}
package attempts to be as RFC-compliant as possible, supporting in
addition to \rfc{2822}, such MIME-related RFCs as
\rfc{2045}, \rfc{2046}, \rfc{2047}, and \rfc{2231}.

The primary distinguishing feature of the \module{email} package is
that it splits the parsing and generating of email messages from the
internal \emph{object model} representation of email.  Applications
using the \module{email} package deal primarily with objects; you can
add sub-objects to messages, remove sub-objects from messages,
completely re-arrange the contents, etc.  There is a separate parser
and a separate generator which handles the transformation from flat
text to the object model, and then back to flat text again.  There
are also handy subclasses for some common MIME object types, and a few
miscellaneous utilities that help with such common tasks as extracting
and parsing message field values, creating RFC-compliant dates, etc.

The following sections describe the functionality of the
\module{email} package.  The ordering follows a progression that
should be common in applications: an email message is read as flat
text from a file or other source, the text is parsed to produce the
object structure of the email message, this structure is manipulated,
and finally rendered back into flat text.

It is perfectly feasible to create the object structure out of whole
cloth --- i.e. completely from scratch.  From there, a similar
progression can be taken as above.

Also included are detailed specifications of all the classes and
modules that the \module{email} package provides, the exception
classes you might encounter while using the \module{email} package,
some auxiliary utilities, and a few examples.  For users of the older
\module{mimelib} package, or previous versions of the \module{email}
package, a section on differences and porting is provided.

\begin{seealso}
    \seemodule{smtplib}{SMTP protocol client}
\end{seealso}

\subsection{Representing an email message}
\input{emailmessage}

\subsection{Parsing email messages}
\input{emailparser}

\subsection{Generating MIME documents}
\input{emailgenerator}

\subsection{Creating email and MIME objects from scratch}
\input{emailmimebase}

\subsection{Internationalized headers}
\input{emailheaders}

\subsection{Representing character sets}
\input{emailcharsets}

\subsection{Encoders}
\input{emailencoders}

\subsection{Exception and Defect classes}
\input{emailexc}

\subsection{Miscellaneous utilities}
\input{emailutil}

\subsection{Iterators}
\input{emailiter}

\subsection{Package History}

Version 1 of the \module{email} package was bundled with Python
releases up to Python 2.2.1.  Version 2 was developed for the Python
2.3 release, and backported to Python 2.2.2.  It was also available as
a separate distutils-based package, and is compatible back to Python 2.1.

\module{email} version 3.0 was released with Python 2.4 and as a separate
distutils-based package.  It is compatible back to Python 2.3.

Here are the differences between \module{email} version 3 and version 2:

\begin{itemize}
\item The \class{FeedParser} class was introduced, and the \class{Parser}
      class was implemented in terms of the \class{FeedParser}.  All parsing
      there for is non-strict, and parsing will make a best effort never to
      raise an exception.  Problems found while parsing messages are stored in
      the message's \var{defect} attribute.

\item All aspects of the API which raised \exception{DeprecationWarning}s in
      version 2 have been removed.  These include the \var{_encoder} argument
      to the \class{MIMEText} constructor, the \method{Message.add_payload()}
      method, the \function{Utils.dump_address_pair()} function, and the
      functions \function{Utils.decode()} and \function{Utils.encode()}.

\item New \exception{DeprecationWarning}s have been added to:
      \method{Generator.__call__()}, \method{Message.get_type()},
      \method{Message.get_main_type()}, \method{Message.get_subtype()}, and
      the \var{strict} argument to the \class{Parser} class.  These are
      expected to be removed in email 3.1.

\item Support for Pythons earlier than 2.3 has been removed.
\end{itemize}

Here are the differences between \module{email} version 2 and version 1:

\begin{itemize}
\item The \module{email.Header} and \module{email.Charset} modules
      have been added.

\item The pickle format for \class{Message} instances has changed.
      Since this was never (and still isn't) formally defined, this
      isn't considered a backward incompatibility.  However if your
      application pickles and unpickles \class{Message} instances, be
      aware that in \module{email} version 2, \class{Message}
      instances now have private variables \var{_charset} and
      \var{_default_type}.

\item Several methods in the \class{Message} class have been
      deprecated, or their signatures changed.  Also, many new methods
      have been added.  See the documentation for the \class{Message}
      class for details.  The changes should be completely backward
      compatible.

\item The object structure has changed in the face of
      \mimetype{message/rfc822} content types.  In \module{email}
      version 1, such a type would be represented by a scalar payload,
      i.e. the container message's \method{is_multipart()} returned
      false, \method{get_payload()} was not a list object, but a single
      \class{Message} instance.

      This structure was inconsistent with the rest of the package, so
      the object representation for \mimetype{message/rfc822} content
      types was changed.  In \module{email} version 2, the container
      \emph{does} return \code{True} from \method{is_multipart()}, and
      \method{get_payload()} returns a list containing a single
      \class{Message} item.

      Note that this is one place that backward compatibility could
      not be completely maintained.  However, if you're already
      testing the return type of \method{get_payload()}, you should be
      fine.  You just need to make sure your code doesn't do a
      \method{set_payload()} with a \class{Message} instance on a
      container with a content type of \mimetype{message/rfc822}.

\item The \class{Parser} constructor's \var{strict} argument was
      added, and its \method{parse()} and \method{parsestr()} methods
      grew a \var{headersonly} argument.  The \var{strict} flag was
      also added to functions \function{email.message_from_file()}
      and \function{email.message_from_string()}.

\item \method{Generator.__call__()} is deprecated; use
      \method{Generator.flatten()} instead.  The \class{Generator}
      class has also grown the \method{clone()} method.

\item The \class{DecodedGenerator} class in the
      \module{email.Generator} module was added.

\item The intermediate base classes \class{MIMENonMultipart} and
      \class{MIMEMultipart} have been added, and interposed in the
      class hierarchy for most of the other MIME-related derived
      classes.

\item The \var{_encoder} argument to the \class{MIMEText} constructor
      has been deprecated.  Encoding  now happens implicitly based
      on the \var{_charset} argument.

\item The following functions in the \module{email.Utils} module have
      been deprecated: \function{dump_address_pairs()},
      \function{decode()}, and \function{encode()}.  The following
      functions have been added to the module:
      \function{make_msgid()}, \function{decode_rfc2231()},
      \function{encode_rfc2231()}, and \function{decode_params()}.

\item The non-public function \function{email.Iterators._structure()}
      was added.
\end{itemize}

\subsection{Differences from \module{mimelib}}

The \module{email} package was originally prototyped as a separate
library called
\ulink{\module{mimelib}}{http://mimelib.sf.net/}.
Changes have been made so that
method names are more consistent, and some methods or modules have
either been added or removed.  The semantics of some of the methods
have also changed.  For the most part, any functionality available in
\module{mimelib} is still available in the \refmodule{email} package,
albeit often in a different way.  Backward compatibility between
the \module{mimelib} package and the \module{email} package was not a
priority.

Here is a brief description of the differences between the
\module{mimelib} and the \refmodule{email} packages, along with hints on
how to port your applications.

Of course, the most visible difference between the two packages is
that the package name has been changed to \refmodule{email}.  In
addition, the top-level package has the following differences:

\begin{itemize}
\item \function{messageFromString()} has been renamed to
      \function{message_from_string()}.

\item \function{messageFromFile()} has been renamed to
      \function{message_from_file()}.

\end{itemize}

The \class{Message} class has the following differences:

\begin{itemize}
\item The method \method{asString()} was renamed to \method{as_string()}.

\item The method \method{ismultipart()} was renamed to
      \method{is_multipart()}.

\item The \method{get_payload()} method has grown a \var{decode}
      optional argument.

\item The method \method{getall()} was renamed to \method{get_all()}.

\item The method \method{addheader()} was renamed to \method{add_header()}.

\item The method \method{gettype()} was renamed to \method{get_type()}.

\item The method \method{getmaintype()} was renamed to
      \method{get_main_type()}.

\item The method \method{getsubtype()} was renamed to
      \method{get_subtype()}.

\item The method \method{getparams()} was renamed to
      \method{get_params()}.
      Also, whereas \method{getparams()} returned a list of strings,
      \method{get_params()} returns a list of 2-tuples, effectively
      the key/value pairs of the parameters, split on the \character{=}
      sign.

\item The method \method{getparam()} was renamed to \method{get_param()}.

\item The method \method{getcharsets()} was renamed to
      \method{get_charsets()}.

\item The method \method{getfilename()} was renamed to
      \method{get_filename()}.

\item The method \method{getboundary()} was renamed to
      \method{get_boundary()}.

\item The method \method{setboundary()} was renamed to
      \method{set_boundary()}.

\item The method \method{getdecodedpayload()} was removed.  To get
      similar functionality, pass the value 1 to the \var{decode} flag
      of the {get_payload()} method.

\item The method \method{getpayloadastext()} was removed.  Similar
      functionality
      is supported by the \class{DecodedGenerator} class in the
      \refmodule{email.Generator} module.

\item The method \method{getbodyastext()} was removed.  You can get
      similar functionality by creating an iterator with
      \function{typed_subpart_iterator()} in the
      \refmodule{email.Iterators} module.
\end{itemize}

The \class{Parser} class has no differences in its public interface.
It does have some additional smarts to recognize
\mimetype{message/delivery-status} type messages, which it represents as
a \class{Message} instance containing separate \class{Message}
subparts for each header block in the delivery status
notification\footnote{Delivery Status Notifications (DSN) are defined
in \rfc{1894}.}.

The \class{Generator} class has no differences in its public
interface.  There is a new class in the \refmodule{email.Generator}
module though, called \class{DecodedGenerator} which provides most of
the functionality previously available in the
\method{Message.getpayloadastext()} method.

The following modules and classes have been changed:

\begin{itemize}
\item The \class{MIMEBase} class constructor arguments \var{_major}
      and \var{_minor} have changed to \var{_maintype} and
      \var{_subtype} respectively.

\item The \code{Image} class/module has been renamed to
      \code{MIMEImage}.  The \var{_minor} argument has been renamed to
      \var{_subtype}.

\item The \code{Text} class/module has been renamed to
      \code{MIMEText}.  The \var{_minor} argument has been renamed to
      \var{_subtype}.

\item The \code{MessageRFC822} class/module has been renamed to
      \code{MIMEMessage}.  Note that an earlier version of
      \module{mimelib} called this class/module \code{RFC822}, but
      that clashed with the Python standard library module
      \refmodule{rfc822} on some case-insensitive file systems.

      Also, the \class{MIMEMessage} class now represents any kind of
      MIME message with main type \mimetype{message}.  It takes an
      optional argument \var{_subtype} which is used to set the MIME
      subtype.  \var{_subtype} defaults to \mimetype{rfc822}.
\end{itemize}

\module{mimelib} provided some utility functions in its
\module{address} and \module{date} modules.  All of these functions
have been moved to the \refmodule{email.Utils} module.

The \code{MsgReader} class/module has been removed.  Its functionality
is most closely supported in the \function{body_line_iterator()}
function in the \refmodule{email.Iterators} module.

\subsection{Examples}

Here are a few examples of how to use the \module{email} package to
read, write, and send simple email messages, as well as more complex
MIME messages.

First, let's see how to create and send a simple text message:

\verbatiminput{email-simple.py}

Here's an example of how to send a MIME message containing a bunch of
family pictures that may be residing in a directory:

\verbatiminput{email-mime.py}

Here's an example of how to send the entire contents of a directory as
an email message:
\footnote{Thanks to Matthew Dixon Cowles for the original inspiration
          and examples.}

\verbatiminput{email-dir.py}

And finally, here's an example of how to unpack a MIME message like
the one above, into a directory of files:

\verbatiminput{email-unpack.py}