:mod:`multifile` --- Support for files containing distinct parts

================================================================

.. module:: multifile

   :synopsis: Support for reading files which contain distinct parts, such as some MIME data.

   :deprecated:

.. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>

.. deprecated:: 2.5

   The :mod:`email` package should be used in preference to the :mod:`multifile`

   module. This module is present only to maintain backward compatibility.

The :class:`MultiFile` object enables you to treat sections of a text file as

file-like input objects, with ``''`` being returned by :meth:`readline` when a

given delimiter pattern is encountered.  The defaults of this class are designed

to make it useful for parsing MIME multipart messages, but by subclassing it and

overriding methods  it can be easily adapted for more general use.

.. class:: MultiFile(fp[, seekable])

   Create a multi-file.  You must instantiate this class with an input object

   argument for the :class:`MultiFile` instance to get lines from, such as a file

   object returned by :func:`open`.

   :class:`MultiFile` only ever looks at the input object's :meth:`readline`,

   :meth:`seek` and :meth:`tell` methods, and the latter two are only needed if you

   want random access to the individual MIME parts. To use :class:`MultiFile` on a

   non-seekable stream object, set the optional *seekable* argument to false; this

   will prevent using the input object's :meth:`seek` and :meth:`tell` methods.

It will be useful to know that in :class:`MultiFile`'s view of the world, text

is composed of three kinds of lines: data, section-dividers, and end-markers.

MultiFile is designed to support parsing of messages that may have multiple

nested message parts, each with its own pattern for section-divider and

end-marker lines.

.. seealso::

   Module :mod:`email`

      Comprehensive email handling package; supersedes the :mod:`multifile` module.

.. _multifile-objects:

MultiFile Objects

-----------------

A :class:`MultiFile` instance has the following methods:

.. method:: MultiFile.readline(str)

   Read a line.  If the line is data (not a section-divider or end-marker or real

   EOF) return it.  If the line matches the most-recently-stacked boundary, return

   ``''`` and set ``self.last`` to 1 or 0 according as the match is or is not an

   end-marker.  If the line matches any other stacked boundary, raise an error.  On

   encountering end-of-file on the underlying stream object, the method raises

   :exc:`Error` unless all boundaries have been popped.

.. method:: MultiFile.readlines(str)

   Return all lines remaining in this part as a list of strings.

.. method:: MultiFile.read()

   Read all lines, up to the next section.  Return them as a single (multiline)

   string.  Note that this doesn't take a size argument!

.. method:: MultiFile.seek(pos[, whence])

   Seek.  Seek indices are relative to the start of the current section. The *pos*

   and *whence* arguments are interpreted as for a file seek.

.. method:: MultiFile.tell()

   Return the file position relative to the start of the current section.

.. method:: MultiFile.next()

   Skip lines to the next section (that is, read lines until a section-divider or

   end-marker has been consumed).  Return true if there is such a section, false if

   an end-marker is seen.  Re-enable the most-recently-pushed boundary.

.. method:: MultiFile.is_data(str)

   Return true if *str* is data and false if it might be a section boundary.  As

   written, it tests for a prefix other than ``'-``\ ``-'`` at start of line (which

   all MIME boundaries have) but it is declared so it can be overridden in derived

   classes.

   Note that this test is used intended as a fast guard for the real boundary

   tests; if it always returns false it will merely slow processing, not cause it

   to fail.

.. method:: MultiFile.push(str)

   Push a boundary string.  When a decorated version of this boundary  is found as

   an input line, it will be interpreted as a section-divider  or end-marker

   (depending on the decoration, see :rfc:`2045`).  All subsequent reads will

   return the empty string to indicate end-of-file, until a call to :meth:`pop`

   removes the boundary a or :meth:`next` call reenables it.

   It is possible to push more than one boundary.  Encountering the

   most-recently-pushed boundary will return EOF; encountering any other

   boundary will raise an error.

.. method:: MultiFile.pop()

   Pop a section boundary.  This boundary will no longer be interpreted as EOF.

.. method:: MultiFile.section_divider(str)

   Turn a boundary into a section-divider line.  By default, this method

   prepends ``'--'`` (which MIME section boundaries have) but it is declared so

   it can be overridden in derived classes.  This method need not append LF or

   CR-LF, as comparison with the result ignores trailing whitespace.

.. method:: MultiFile.end_marker(str)

   Turn a boundary string into an end-marker line.  By default, this method

   prepends ``'--'`` and appends ``'--'`` (like a MIME-multipart end-of-message

   marker) but it is declared so it can be overridden in derived classes.  This

   method need not append LF or CR-LF, as comparison with the result ignores

   trailing whitespace.

Finally, :class:`MultiFile` instances have two public instance variables:

.. attribute:: MultiFile.level

   Nesting depth of the current part.

.. attribute:: MultiFile.last

   True if the last end-of-file was for an end-of-message marker.

.. _multifile-example:

:class:`MultiFile` Example

--------------------------

.. sectionauthor:: Skip Montanaro <skip@pobox.com>

::

   import mimetools

   import multifile

   import StringIO

   def extract_mime_part_matching(stream, mimetype):

       """Return the first element in a multipart MIME message on stream

       matching mimetype."""

       msg = mimetools.Message(stream)

       msgtype = msg.gettype()

       params = msg.getplist()

       data = StringIO.StringIO()

       if msgtype[:10] == "multipart/":

           file = multifile.MultiFile(stream)

           file.push(msg.getparam("boundary"))

           while file.next():

               submsg = mimetools.Message(file)

               try:

                   data = StringIO.StringIO()

                   mimetools.decode(file, data, submsg.getencoding())

               except ValueError:

                   continue

               if submsg.gettype() == mimetype:

                   break

           file.pop()

       return data.getvalue()