<type>real</type> and <type>double</type> are converted to
       Python <type>float</type>.
      </para>
     </listitem>

     <listitem>
      <para>
       PostgreSQL <type>numeric</type> is converted to
       Python <type>Decimal</type>.  This type is imported from
       the <literal>cdecimal</literal> package if that is available.
       Otherwise,
       <literal>decimal.Decimal</literal> from the standard library will be
       used.  <literal>cdecimal</literal> is significantly faster
       than <literal>decimal</literal>.  In Python 3.3 and up,
       however, <literal>cdecimal</literal> has been integrated into the
       standard library under the name <literal>decimal</literal>, so there is
       no longer any difference.
      </para>
     </listitem>

     <listitem>
      <para>
       PostgreSQL <type>bytea</type> is converted to Python <type>bytes</type>.
      </para>
     </listitem>

     <listitem>
      <para>
       All other data types, including the PostgreSQL character string types,
       are converted to a Python <type>str</type> (in Unicode like all Python
       strings).
      </para>
     </listitem>

     <listitem>
      <para>
       For nonscalar data types, see below.
      </para>
     </listitem>
    </itemizedlist>
   </para>

   <para>
    When a PL/Python function returns, its return value is converted to the
    function's declared PostgreSQL return data type as follows:

    <itemizedlist>
     <listitem>
      <para>
       When the PostgreSQL return type is <type>boolean</type>, the
       return value will be evaluated for truth according to the
       <emphasis>Python</emphasis> rules.  That is, 0 and empty string
       are false, but notably <literal>'f'</literal> is true.
      </para>
     </listitem>

     <listitem>
      <para>
       When the PostgreSQL return type is <type>bytea</type>, the return value
       will be converted to Python <type>bytes</type> using the respective
       Python built-ins, with the result being converted to
       <type>bytea</type>.
      </para>
     </listitem>

     <listitem>
      <para>
       For all other PostgreSQL return types, the return value is converted
       to a string using the Python built-in <literal>str</literal>, and the
       result is passed to the input function of the PostgreSQL data type.
       (If the Python value is a <type>float</type>, it is converted using
       the <literal>repr</literal> built-in instead of <literal>str</literal>, to
       avoid loss of precision.)
      </para>

      <para>
       Strings are automatically converted to the PostgreSQL server encoding
       when they are passed to PostgreSQL.
      </para>
     </listitem>

     <listitem>
      <para>
       For nonscalar data types, see below.
      </para>
     </listitem>
    </itemizedlist>

    Note that logical mismatches between the declared PostgreSQL
    return type and the Python data type of the actual return object
    are not flagged; the value will be converted in any case.
   </para>
  </sect2>

  <sect2 id="plpython-data-null">
   <title>Null, None</title>
  <para>
   If an SQL null value<indexterm><primary>null value</primary><secondary
   sortas="PL/Python">in PL/Python</secondary></indexterm> is passed to a
   function, the argument value will appear as <symbol>None</symbol> in
   Python. For example, the function definition of <function>pymax</function>
   shown in <xref linkend="plpython-funcs"/> will return the wrong answer for null
   inputs. We could add <literal>STRICT</literal> to the function definition
   to make <productname>PostgreSQL</productname> do something more reasonable:
   if a null value is passed, the function will not be called at all,
   but will just return a null result automatically. Alternatively,
   we could check for null inputs in the function body:

<programlisting>
CREATE FUNCTION pymax (a integer, b integer)
  RETURNS integer
AS $$
  if (a is None) or (b is None):
    return None