Jython Hints and Tips

This page contains ideas for using Jython with the JSR223 Script Engine in Openhab.

• Using traceback for better stack traces
• Exploring the Jython API
• Fixing missing getRules() error
• Easier logging

Using traceback for better stack traces

Without help, the JSR223 engine simply prints a Java stack trace, from which it is difficult to determine the error. Using the Python traceback module gives useful error indications.

import traceback

class TestRule(Rule):
    def getEventTrigger(self):
        return [
            TimerTrigger("0/50 * * * * ?")
        ]

    def execute(self, event):
        try:
            self.foo = unknown_bar  # error
        except:
            oh.logError("TestRule", traceback.format_exc())

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Exploring the openHAB Jython API

If you need to know the specific interface for a openHAB-specific type, you can create a simple Jython script to log some information. A Jython script isn't required to contain rules (although it must contain a getRules function even if it returns an empty RuleSet). Any top-level statements will be evaluated by Jython. Let's say you want to know what functions can be called on an openHAB Item.

Example items/test.items

String TestString

Example scripts/test.py

item = ir.getItem("TestString")
oh.logInfo("TEST", str(type(item)))
oh.logInfo("TEST", str(dir(item)))

# no rules in this script
def getRules():
  return RuleSet([])

Note: The arguments to openHAB's log methods must be a string. The standard Python dir function returns a string list so str is used to format it as a string. The standard Python type function returns a Java type wrapper (in Jython) that also must be formatted as a string.

Log file output

2016-05-15 16:46:08.120 [INFO ] [o.c.j.i.e.scriptmanager.Script] - Loading Script test.py
2016-05-15 16:46:08.126 [INFO ] [o.c.j.i.e.scriptmanager.Script] - EngineName: jython
2016-05-15 16:46:08.705 [INFO ] [org.openhab.model.jsr223.TEST ] - <type 'org.openhab.core.library.items.StringItem'>
2016-05-15 16:46:08.713 [INFO ] [org.openhab.model.jsr223.TEST ] - ['__class__', '__copy__', '__deepcopy__', '__delattr__', 
'__doc__', '__ensure_finalizer__', '__eq__', '__format__', '__getattribute__', '__hash__', '__init__', '__ne__', '__new__', 
'__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__subclasshook__', '__unicode__', 
'acceptedCommandTypes', 'acceptedDataTypes', 'addStateChangeListener', 'class', 'dispose', 'equals', 
'eventPublisher', 'getAcceptedCommandTypes', 'getAcceptedDataTypes', 'getClass', 'getGroupNames', 
'getName', 'getState', 'getStateAs', 'groupNames', 'hashCode', 'initialize', 'name', 'notify', 
'notifyAll', 'removeStateChangeListener', 'setEventPublisher', 'setState', 'state', 'toString', 'wait']

Note: In Jython, any Java method that starts with "get" and has no arguments can be accessed like a Python property. So state = item.getState() becomes state = item.state. Similarly, any Java method that starts with "set" and has one argument can be accessed like Python property. So item.setState(value) becomes item.state = value.

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Script file misses mandatory function: getRules()

This error appears to be caused by the Java file reader reading the file faster than the code is written by the editor. I have removed its occurrence by updating openhab.cfg to not read the script files as quickly

folder:items=10,items
folder:sitemaps=10,sitemap
folder:rules=10,rules
folder:scripts=50,script
folder:persistence=10,persist

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Easier Logging

Creating a super class that automatically creates a logger with using the rule class name. Note that TestRule inherits from OpenhabRule, and calls its parents initializer.

class OpenhabRule(Rule):
    def __init__(self):
        self.log = oh.getLogger(type(self).__name__)

class TestRule(OpenhabRule):
    def __init__(self):
        super(TestRule, self).__init__()

    def getEventTrigger(self):
        return [
            TimerTrigger("0/50 * * * * ?")
        ]


    def execute(self, event):
        self.log.debug("event received: {}", event)

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