Introduction

Welcome to the world of scripting in openLCA! Since openLCA is a Java-based application running on the Java Virtual Machine (JVM), it comes with a powerful tool for automation and customization: Jython. Jython is an implementation of Python 2.7 that seamlessly integrates with Java, compiling Python code into Java bytecode for execution on the JVM.

The best part? openLCA comes pre-packaged with Jython 2.7, so you are ready to start scripting right away! Just head over to Tools → Developer Tools → Python, where you will find a built-in Python editor. There, you can write and execute scripts to automate tasks, extend functionalities, or simply experiment with the power of Python inside openLCA.

Let’s dive in and unlock the full potential of openLCA with Jython!

Open the Python editor

In order to execute a script, you click on the Run button in the toolbar of the Python editor:

Run a script in openLCA

Hello world!

As said above, you can write Python code in the Python editor and execute it. Let's start with the holy grail of coding tutorials: Hello world!

print("Hello world!")

When running this line of code, the openLCA console should appear with the message "Hello world!"

The script is executed in the same Java process as openLCA. Thus, you have access to all the things that you can do with openLCA via this scripting API (and also to everything that you can do with the Java and Jython runtime). Here is a small example script that will show the information message box when you execute it in openLCA:

from org.openlca.app.util import MsgBox

MsgBox.info("Hello from Python (Jython)!")

Hello from Jython

Relation to standard Python

As said above, Jython runs on the JVM. It implements a great part of the Python 2.7 standard library for the JVM. For example the following script will work when you set the file path to an existing CSV file on your system:

import csv

FILE = "~/path/to/file.csv"
data = [
    ["Tea", "1.0"],
    ["Coffee", "2.0"],
]

with open(FILE, "w") as file:
    writer = csv.writer(file)
    for r in data:
        writer.writerow(r)

The Jython standard library is extracted to the python folder of the openLCA workspace which is by default located in your user directory ~/openLCA-data-1.4/python. This is also the location in which you can put your own Jython 2.7 compatible modules. For example, when you create a file tutorial.py with the following function in this folder:

# ~/openLCA-data-1.4/python/tutorial.py
def the_answer():
    return 42

You can then load it in the openLCA script editor:

import tutorial
import org.openlca.app.util.MsgBox as MsgBox

MsgBox.info("The answer is %s!" % tutorial.the_answer())

An important thing to note is that Python modules that use C-extensions (like NumPy and friends) or parts of the standard library that are not implemented in Jython are not compatible with Jython. If you want to interact from standard CPython with openLCA (using Pandas, NumPy, etc.) you can use the openLCA IPC Python API.

The openLCA API

As said above, with Jython you directly access the openLCA Java API. In Jython, you interact with a Java class in the same way as with a Python class. The openLCA API starts with a set of classes that describe the basic data model, like Flow, Process, ProductSystem. You can find these classes in the olca-module repository.

More information in the The basic data model chapter.