# Server-side ("preloaded") script return value
**URL:** https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218
**Category:** Elasticsearch
**Created:** [November 1, 2013, 4:36pm UTC](https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218 "2013-11-01T16:36:45Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@rastro](https://discuss.elastic.co/u/rastro)
#### Post date: [November 1, 2013, 4:36pm UTC](https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218/1 "2013-11-01T16:36:45Z")
I have a query that calls a python script. That part is working finally,
which is confirmed by the script's output to a log file.
Now, I need to get the value back to the query, but I only ever see
"my\_field" : null
in the response.
How am I supposed to return the value from the script to the query? I'm
currently sending it back on stdout.
```
"script_fields" : {
"my_field": {
"script": "testscript",
"params": {
"field": "value1",
"tag" : "value2"
},
"type": "float",
"lang": "python"
}
}
```
But the response is always:
{
"\_index" : "logstash-2013.11.01",
"\_type" : "app",
"\_id" : "rV5JRvZySaS6gwdT6pPvyw",
"\_score" : 0.36469176, "\_source" : {...},
"fields" : {
"my\_field" : null
}
}
The end of the python script:
sys.stdout.write(ret)
sys.stdout.write("\n")
sys.stdout.flush()
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---
### Author:  [@javanna](https://discuss.elastic.co/u/javanna)
#### Post date: [November 4, 2013, 5:41pm UTC](https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218/2 "2013-11-04T17:41:06Z")
Hi,
script fields are meant to create on-the-fly new fields which can be
returned for each document that matches a query. Can you elaborate on why
you need to send the result of the script back to the query?
On Friday, November 1, 2013 5:36:45 PM UTC+1, rastro wrote:
> I have a query that calls a python script. That part is working finally,
> which is confirmed by the script's output to a log file.
>
> Now, I need to get the value back to the query, but I only ever see
> "my\_field" : null
> in the response.
>
> How am I supposed to return the value from the script to the query? I'm
> currently sending it back on stdout.
>
> ```
> "script_fields" : {
> "my_field": {
> "script": "testscript",
> "params": {
> "field": "value1",
> "tag" : "value2"
> },
> "type": "float",
> "lang": "python"
> }
> }
>
> ```
>
> But the response is always:
>
> {
> "\_index" : "logstash-2013.11.01",
> "\_type" : "app",
> "\_id" : "rV5JRvZySaS6gwdT6pPvyw",
> "\_score" : 0.36469176, "\_source" : {...},
> "fields" : {
> "my\_field" : null
> }
> }
>
> The end of the python script:
>
> sys.stdout.write(ret)
> sys.stdout.write("\n")
> sys.stdout.flush()
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---
### Author:  [@rastro](https://discuss.elastic.co/u/rastro)
#### Post date: [November 6, 2013, 4:52pm UTC](https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218/3 "2013-11-06T16:52:39Z")
Luca pointed out that ES calls python with an 'eval', so multi-line scripts
won't work on the server side, either. There's some info in this jython
ticket:
```
http://bugs.jython.org/issue1713 .
```
I switched to javascript and am able to get the field back for facets and
script\_fields.
Thanks, Luca.
On Monday, November 4, 2013 9:41:06 AM UTC-8, Luca Cavanna wrote:
> Hi,
> script fields are meant to create on-the-fly new fields which can be
> returned for each document that matches a query. Can you elaborate on why
> you need to send the result of the script back to the query?
>
> On Friday, November 1, 2013 5:36:45 PM UTC+1, rastro wrote:
>
> > I have a query that calls a python script. That part is working finally,
> > which is confirmed by the script's output to a log file.
> >
> > Now, I need to get the value back to the query, but I only ever see
> > "my\_field" : null
> > in the response.
> >
> > How am I supposed to return the value from the script to the query? I'm
> > currently sending it back on stdout.
> >
> > ```
> > "script_fields" : {
> > "my_field": {
> > "script": "testscript",
> > "params": {
> > "field": "value1",
> > "tag" : "value2"
> > },
> > "type": "float",
> > "lang": "python"
> > }
> > }
> >
> > ```
> >
> > But the response is always:
> >
> > {
> > "\_index" : "logstash-2013.11.01",
> > "\_type" : "app",
> > "\_id" : "rV5JRvZySaS6gwdT6pPvyw",
> > "\_score" : 0.36469176, "\_source" : {...},
> > "fields" : {
> > "my\_field" : null
> > }
> > }
> >
> > The end of the python script:
> >
> > sys.stdout.write(ret)
> > sys.stdout.write("\n")
> > sys.stdout.flush()
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 6, 2017, 2:08am UTC](https://discuss.elastic.co/t/server-side-preloaded-script-return-value/14218/4 "2017-07-06T02:08:31Z")