openLCA Python Tutorial
openLCA is a Java application
and, thus, runs on the Java Virtual Machine (JVM). Jython
is a Python 2.7 implementation that runs on the JVM. It compiles Python code to
Java bytecode which is then executed on the JVM. The final release of Jython 2.7
is bundled with openLCA. Under Window > Developer tools > Python you can
find a small Python editor where you can write and execute Python scripts:
In order to execute a script, you click on the Run button in the toolbar of
the Python editor:
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 dialog below when you execute it in openLCA:
from org.openlca.app.util import UI, Dialog
from org.openlca.app import App
def say_hello():
Dialog.showInfo(UI.shell(), 'Hello from Python (Jython)!')
if __name__ == '__main__':
App.runInUI('say hello', say_hello)
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 a valid path on your system:
import csv
with open('path/to/file.csv', 'w') as stream:
writer = csv.writer(stream)
writer.writerow(["data you", "may want", "to export",])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():
f = lambda s, x: s + x if x % 2 == 0 else s
return reduce(f, range(0, 14))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.
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Content
License
This project is in the worldwide public domain, released under the CC0 1.0 Universal Public Domain Dedication.
