ExtApp python - ERROR 503

[freshmen]

want to give ability to execute any python script via ExtApp-ScriptHandler

<scriptHandler>
<suffix>py</suffix>
<type>fcgi</type>
<handler>pt</handler>
<note></note>
</scriptHandler>

<extProcessor>
<type>fcgi</type>
<name>pt</name>
<address>UDS://tmp/lshttpd/pt.sock</address>
<note></note>
<maxConns>20</maxConns>
<initTimeout>60</initTimeout>
<retryTimeout>0</retryTimeout>
<persistConn></persistConn>
<pcKeepAliveTimeout></pcKeepAliveTimeout>
<respBuffer>0</respBuffer>
<autoStart>1</autoStart>
<path>/usr/bin/python</path>
<backlog></backlog>
<instances>20</instances>
<runOnStartUp></runOnStartUp>
<extMaxIdleTime></extMaxIdleTime>
<priority></priority>
<memSoftLimit>250M</memSoftLimit>
<memHardLimit>250M</memHardLimit>
<procSoftLimit>200</procSoftLimit>
<procHardLimit>200</procHardLimit>
</extProcessor>

always got the same error:
HTTP request sent, awaiting response... 503 Service Unavailable
15:21:23 ERROR 503: Service Unavailable.

it is possibly to execute scripts with ScriptHandler?
if so, where is my mistake?