question Re: How to update FlowFile attributes in Python now that Jython is removed? in Support Questions

How to update FlowFile attributes in Python now that Jython is removed?

Ghilani — Mon, 25 Aug 2025 10:22:26 GMT

In NiFi 2.4 and above, the Jython engine is no longer available in ExecuteScript.
Previously, I used scripts like this to read and update attributes:

val = flowFile.getAttribute('x')
flowFile = session.putAttribute(flowFile, 'x', str(int(val) + 10))

Now I want to do the same using Python in NiFi 2.4+:

Read an attribute (e.g., x)
Compute a new value
Write it back as an attribute (or a new one)
Keep the original FlowFile content unchanged

What’s the recommended way in NiFi 2.4+?

Any official docs, samples, or best practices for this scenario would be very helpful.

Re: How to update FlowFile attributes in Python now that Jython is removed?

RAGHUY — Fri, 05 Sep 2025 11:25:43 GMT

In NiFi 2.4 and above, the built-in Jython (Python 2 interpreter) for ExecuteScript has been removed, so the traditional approach using inline Python is no longer supported. There is, however, a modern and robust alternative using NiFi's first-class Python processor support for attribute manipulation, or using Groovy/Clojure in ExecuteScript, or simply leveraging UpdateAttribute for simple logic.

https://nifi.apache.org/nifi-docs/python-developer-guide.html
https://nifi.apache.org/components/org.apache.nifi.processors.script.ExecuteScript/

Re: How to update FlowFile attributes in Python now that Jython is removed?

Ghilani — Fri, 05 Sep 2025 12:36:21 GMT

That approach is not feasible. Adopting a new programming language is impractical given the large number of existing Python scripts that I cannot realistically migrate. The second option is also suboptimal, since creating a dedicated NiFi processor for each script would introduce significant overhead. Furthermore, each custom processor would run in its own isolated virtual environment, leading to excessive heap consumption

Re: How to update FlowFile attributes in Python now that Jython is removed?

Ghilani — Fri, 05 Sep 2025 12:39:32 GMT

However, I was able to resolve this by leveraging ExecuteStreamCommand (ESC). Specifically, I used the Output Destination Attribute property to push the required attributes into it, which I can then process separately.