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<H2><A NAME="SECTION0014230000000000000000">
12.2.3 Generating MIME documents</A>
</H2>
<A NAME="module-email.Generator"></A>
<P>
One of the most common tasks is to generate the flat text of the email
message represented by a message object structure. You will need to do
this if you want to send your message via the <tt class="module"><a href="module-smtplib.html">smtplib</a></tt>
module or the <tt class="module"><a href="module-nntplib.html">nntplib</a></tt> module, or print the message on the
console. Taking a message object structure and producing a flat text
document is the job of the <tt class="class">Generator</tt> class.
<P>
Again, as with the <tt class="module"><a href="module-email.Parser.html">email.Parser</a></tt> module, you aren't limited
to the functionality of the bundled generator; you could write one
from scratch yourself. However the bundled generator knows how to
generate most email in a standards-compliant way, should handle MIME
and non-MIME email messages just fine, and is designed so that the
transformation from flat text, to a message structure via the
<tt class="class">Parser</tt> class, and back to flat text, is idempotent (the input
is identical to the output).
<P>
Here are the public methods of the <tt class="class">Generator</tt> class:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-3885' xml:id='l2h-3885' class="class">Generator</tt></b>(</nobr></td>
<td><var>outfp</var><big>[</big><var>, mangle_from_</var><big>[</big><var>,
maxheaderlen</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
The constructor for the <tt class="class">Generator</tt> class takes a file-like
object called <var>outfp</var> for an argument. <var>outfp</var> must support
the <tt class="method">write()</tt> method and be usable as the output file in a
Python extended print statement.
<P>
Optional <var>mangle_from_</var> is a flag that, when <code>True</code>, puts a
"<tt class="samp">></tt>" character in front of any line in the body that starts exactly as
"<tt class="samp">From </tt>", i.e. <code>From</code> followed by a space at the beginning of the
line. This is the only guaranteed portable way to avoid having such
lines be mistaken for a Unix mailbox format envelope header separator (see
<a class="ulink" href="http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html"
>WHY THE CONTENT-LENGTH FORMAT IS BAD</a>
for details). <var>mangle_from_</var> defaults to <code>True</code>, but you
might want to set this to <code>False</code> if you are not writing Unix
mailbox format files.
<P>
Optional <var>maxheaderlen</var> specifies the longest length for a
non-continued header. When a header line is longer than
<var>maxheaderlen</var> (in characters, with tabs expanded to 8 spaces),
the header will be split as defined in the <tt class="module">email.Header</tt>
class. Set to zero to disable header wrapping. The default is 78, as
recommended (but not required) by <a class="rfc" id='rfcref-91012' xml:id='rfcref-91012'
href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a>.
</dl>
<P>
The other public <tt class="class">Generator</tt> methods are:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3886' xml:id='l2h-3886' class="method">flatten</tt></b>(</nobr></td>
<td><var>msg</var><big>[</big><var>, unixfrom</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Print the textual representation of the message object structure rooted at
<var>msg</var> to the output file specified when the <tt class="class">Generator</tt>
instance was created. Subparts are visited depth-first and the
resulting text will be properly MIME encoded.
<P>
Optional <var>unixfrom</var> is a flag that forces the printing of the
envelope header delimiter before the first <a class="rfc" id='rfcref-91014' xml:id='rfcref-91014'
href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a> header of the
root message object. If the root object has no envelope header, a
standard one is crafted. By default, this is set to <code>False</code> to
inhibit the printing of the envelope delimiter.
<P>
Note that for subparts, no envelope header is ever printed.
<P>
<span class="versionnote">New in version 2.2.2.</span>
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3887' xml:id='l2h-3887' class="method">clone</tt></b>(</nobr></td>
<td><var>fp</var>)</td></tr></table></dt>
<dd>
Return an independent clone of this <tt class="class">Generator</tt> instance with
the exact same options.
<P>
<span class="versionnote">New in version 2.2.2.</span>
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3888' xml:id='l2h-3888' class="method">write</tt></b>(</nobr></td>
<td><var>s</var>)</td></tr></table></dt>
<dd>
Write the string <var>s</var> to the underlying file object,
i.e. <var>outfp</var> passed to <tt class="class">Generator</tt>'s constructor. This
provides just enough file-like API for <tt class="class">Generator</tt> instances to
be used in extended print statements.
</dl>
<P>
As a convenience, see the methods <tt class="method">Message.as_string()</tt> and
<code>str(aMessage)</code>, a.k.a. <tt class="method">Message.__str__()</tt>, which
simplify the generation of a formatted string representation of a
message object. For more detail, see <tt class="module"><a href="module-email.Message.html">email.Message</a></tt>.
<P>
The <tt class="module">email.Generator</tt> module also provides a derived class,
called <tt class="class">DecodedGenerator</tt> which is like the <tt class="class">Generator</tt>
base class, except that non-<span class="mimetype">text</span> parts are substituted with
a format string representing the part.
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-3889' xml:id='l2h-3889' class="class">DecodedGenerator</tt></b>(</nobr></td>
<td><var>outfp</var><big>[</big><var>, mangle_from_</var><big>[</big><var>,
maxheaderlen</var><big>[</big><var>, fmt</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
<P>
This class, derived from <tt class="class">Generator</tt> walks through all the
subparts of a message. If the subpart is of main type
<span class="mimetype">text</span>, then it prints the decoded payload of the subpart.
Optional <var>_mangle_from_</var> and <var>maxheaderlen</var> are as with the
<tt class="class">Generator</tt> base class.
<P>
If the subpart is not of main type <span class="mimetype">text</span>, optional <var>fmt</var>
is a format string that is used instead of the message payload.
<var>fmt</var> is expanded with the following keywords, "<tt class="samp">%(keyword)s</tt>"format:
<P>
<UL>
<LI><code>type</code> - Full MIME type of the non-<span class="mimetype">text</span> part
<P>
</LI>
<LI><code>maintype</code> - Main MIME type of the non-<span class="mimetype">text</span> part
<P>
</LI>
<LI><code>subtype</code> - Sub-MIME type of the non-<span class="mimetype">text</span> part
<P>
</LI>
<LI><code>filename</code> - Filename of the non-<span class="mimetype">text</span> part
<P>
</LI>
<LI><code>description</code> - Description associated with the
non-<span class="mimetype">text</span> part
<P>
</LI>
<LI><code>encoding</code> - Content transfer encoding of the
non-<span class="mimetype">text</span> part
<P>
</LI>
</UL>
<P>
The default value for <var>fmt</var> is <code>None</code>, meaning
<P>
<div class="verbatim"><pre>
[Non-text (%(type)s) part of message omitted, filename %(filename)s]
</pre></div>
<P>
<span class="versionnote">New in version 2.2.2.</span>
</dl>
<P>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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