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<title>4.9.1.1 Codec Objects </title>
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<H3><A NAME="SECTION006911000000000000000"></A><A NAME="codec-objects"></A>
<BR>
4.9.1.1 Codec Objects
</H3>

<P>
The <tt class="class">Codec</tt> class defines these methods which also define the
function interfaces of the stateless encoder and decoder:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1005' xml:id='l2h-1005' class="method">encode</tt></b>(</nobr></td>
  <td><var>input</var><big>[</big><var>, errors</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Encodes the object <var>input</var> and returns a tuple (output object,
  length consumed).  While codecs are not restricted to use with Unicode, in
  a Unicode context, encoding converts a Unicode object to a plain string
  using a particular character set encoding (e.g., <code>cp1252</code> or
  <code>iso-8859-1</code>).

<P>
<var>errors</var> defines the error handling to apply. It defaults to
  <code>'strict'</code> handling.

<P>
The method may not store state in the <tt class="class">Codec</tt> instance. Use
  <tt class="class">StreamCodec</tt> for codecs which have to keep state in order to
  make encoding/decoding efficient.

<P>
The encoder must be able to handle zero length input and return an
  empty object of the output object type in this situation.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1006' xml:id='l2h-1006' class="method">decode</tt></b>(</nobr></td>
  <td><var>input</var><big>[</big><var>, errors</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Decodes the object <var>input</var> and returns a tuple (output object,
  length consumed).  In a Unicode context, decoding converts a plain string
  encoded using a particular character set encoding to a Unicode object.

<P>
<var>input</var> must be an object which provides the <code>bf_getreadbuf</code>
  buffer slot.  Python strings, buffer objects and memory mapped files
  are examples of objects providing this slot.

<P>
<var>errors</var> defines the error handling to apply. It defaults to
  <code>'strict'</code> handling.

<P>
The method may not store state in the <tt class="class">Codec</tt> instance. Use
  <tt class="class">StreamCodec</tt> for codecs which have to keep state in order to
  make encoding/decoding efficient.

<P>
The decoder must be able to handle zero length input and return an
  empty object of the output object type in this situation.
</dl>

<P>
The <tt class="class">StreamWriter</tt> and <tt class="class">StreamReader</tt> classes provide
generic working interfaces which can be used to implement new
encodings submodules very easily. See <tt class="module">encodings.utf_8</tt> for an
example on how this is done.

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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