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JMRI: Scripting "How To..."

Some hints and examples on how to do basic operations in scripts

NOTE REGARDING CODE EXAMPLES: The Python language provides alternative ways of addressing objects and methods; examples may use one or the other syntax, as:

      m = memories.provideMemory("IMXXX")
      m.value = "Anything"
      memories.provideMemory("IMYYY").setValue("Anything else")

No assignment operator (=) is necessary in the second example as the "set" method does that work. Use whichever syntax you prefer, although it is a good practice to be consistent.

See the examples page for many sample scripts. Also, the introductory page shows some of the basic commands.

See also Python/Jython Language for general FAQ about the language.

See also Jython Scripting "What... Where" for other interesting tidbits.

How do I run a saved script?

From the PanelPro main screen, click on Scripting {Old: Panels} in the top menu. Or, from the DecoderPro main screen, click on Actions in the top menu. Select Run Script... from the dropdown.

The directory set up in Preferences (which you can change) will appear and you can select a script to run. YOu can also navigate to any other directory that contains stored scripts. [On PCs, Jython script files have a ".py" suffix standing for Python.]

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How should I name variables in JMRI scripts?

Short answer: you can name them any way you like!

In many of the sample files, turnouts are referred to by names like "to12", signals by names like "si21", and sensors by names like "bo45". These conventions grew out of how some older code was written, and they can make the code clearer. But they are in no way required; the program doesn't care what you call variables.

For example, "self.to12" is just the name of a variable. You can call it anything you want, e.g. self.MyBigFatNameForTheLeftTurnout

The "self" part makes it completely local; "self" refers to "an object of the particular class I'm defining right now". Alternately, you can define a global variable, but that's not recommended. If you have multiple scripts running (and you can have as many as you'd like; we recommend that you put each signal head in a separate one), the variables can get confused if you use the same variable name to mean too different things. Using "self" like this one does makes sure that doesn't happen.

Note that turnouts, etc, do have "System Names" that look like "LT12". You'll see those occasionally, but that's something different from the variable names in a script file.

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How do I reference existing or create new JMRI objects (sensors, memories, etc.) in a script?

All of the JMRI input and output objects listed in Common Tools, such as sensors, memories, lights, signals, reporters, etc., can be accessed or new ones created within a script. A simple line of code typed into the Script Entry window is all it takes to create an object:

    a=memories.provideMemory("IM" + "XXX")
    b=sensors.provideSensor("IS" + "XXX")

Using the "provide" method for a specific type of input or output either creates a new object with the system name specified (IMXXX or ISXXX in these examples) or finds a reference to an existing object. These lines can also be included in scripts that are saved and then run.

Using the "get" method, on the other hand, will find an existing object but will not create a new one. If your goal is to only find existing objects, you could use code like the following, where SomeSensorName is a variable with either a system name or a user name (see below):

    c = sensors.getSensor(SomeSensorName)
    if c is None:
       print SomeSensorName," does not exist"

Once a reference is established, variables within an object can be set using statements like:

    a.userName = "My memory 1"
    b.userName = "My Sensor 1 at East Yard"
    a.value = "Something I want to save"
    b.state = ACTIVE

How do I use non ISO 8859-1 characters in user objects and aspects?

User Names of JMRI Object and Signal Aspects may include non ISO 8859-1 characters. You need to decode them properly to use these names in jython scripts. All strings that contain non ISO 8859-1 characters must be decoded by the .decode ("UTF-8") method.

Example: Distant signal of the Entry signal of the Czechoslovak State Railways JMRI "ČSD 1962 základní návěstidla: Předvěsti" Appearance Table according to the rules is called PřL. The signal mast will display two aspects: Clear – Volno and Caution – Výstraha.

In the table of Signal masts is distant signal mast with LocoNet DCC address 100 with system name LF$dsm:CSD-1962-zakladni:entry_distant(100).

In the script, the signal mast and its aspects will work as follows:

Window Script Entry:

    mastDistantUserName = "PřL".decode("UTF-8")
    aspectClear = "Volno"
    aspectCaution = "Výstraha".decode("UTF-8")

    mastDistant = masts.getSignalMast(mastDistantUserName)
    print "System Name:    ", mastDistant.getSystemName()
    print "User Name:      ", mastDistant.getUserName()

    print "aspect default: ", mastDistant.getAspect()

    print "aspect Clear:   ", mastDistant.getAspect()

    print "aspect Caution: ", mastDistant.getAspect()

Window Script Output:

    System Name:     LF$dsm:CSD-1962-zakladni:entry_distant(100)
    User Name:       PřL
    aspect default:  None
    aspect Clear:    Volno
    aspect Caution:  Výstraha

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How do I print slot monitor data?

The slot table keeps track of locomotives and consists controlled by JMRI. To print the contents, extract the data line by line and send to the printer. Here is an example using the LocoNet slot table:

    myLocoNetConnection = jmri.InstanceManager.getList(jmri.jmrix.loconet.LocoNetSystemConnectionMemo).get(0);
    slotManager = myLocoNetConnection.getSlotManager()
    for i in range(0, 127):
       print slotManager.slot(i).slotStatus

SystemConnectionMemo is available for many types of DCC communication systems. See JavaDocs for more information.

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How can I limit the priority of a script?

If the script runs a loop that's supposed to update something, it can't be written to run continuously or else it will just suck up as much computer time as it can. Rather, it should wait.

The best thing to do is to wait for something to change. For example, if your script looks at some sensors to decide what to do, wait for one of those sensors to change (see below and the sample scripts for examples)

Simpler, but not as efficient, is to just wait for a little while before checking again. For example

causes an automaton or Siglet script to wait for 1000 milliseconds (one second) before continuing.

For just a simple script, something that doesn't use the Automat or Siglet classes, you can sleep by doing

    from time import sleep

The first line defines the "sleep" routine, and only needs to be done once. The second line then sleeps for 10 seconds. Note that the accuracy of this method is not as good as using one of the special classes.

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How do I wait for something(s) to change on my layout?

If your script is based on a Siglet or AbstractAutomaton class (e.g. if you're writing a "handle" routine" - see What...Where page for more info on these classes), there's a general "waitChange" routine which waits for any of several sensors to change before returning to you. Note that more than one may change at the same time, so you can't assume that just one has a different value! And you'll then have to check whether they've become some particular state. It's written as:

    self.waitChange([self.sensorA, self.sensorB, self.sensorC])
where you've previously defined each of those "self.sensorA" things via a line like:
    self.sensorA = sensors.provideSensor("21")
You can then check for various combinations like:
   if self.sensorA.knownState == ACTIVE :
        print "The plane! The plane!"
   elif self.sensorB.knownState == INACTIVE :
        print "Would you believe a really fast bird?"
        print "Nothing to see here, move along..."
You can also wait for any changes in objects of multiple types:
    self.waitChange([self.sensorA, self.turnoutB, self.signalC])
Finally, you can specify the maximum time to wait before continuing even though nothing has changed:
    self.waitChange([self.sensorA, self.sensorB, self.sensorC], 5000)
will wait a maximum of 5000 milliseconds, e.g. 5 seconds. If nothing has changed, the script will continue anyway.

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How do I "listen" to a Turnout or Sensor?

JMRI objects (Turnouts, Sensors, etc) can have "Listeners" attached to them. These are then notified when the status of the object changes. If you're using the Automat or Siglet classes, you don't need to use this capability; those classes handle all the creationg and registering of listeners. But if you want to do something special, you may need to use that capability.

A single routine can listen to one or more Turnout, Sensor, etc.

If you retain a reference to your listener object, you can attach it to more than one object:

    m = MyListener()

But how does the listener know what changed?

A listener routine looks like this:

class MyListener(java.beans.PropertyChangeListener):
  def propertyChange(self, event):
    print "change",event.propertyName
    print "from", event.oldValue, "to", event.newValue
    print "source systemName", event.source.systemName
    print "source userName", event.source.userName

When the listener is called, it's given an object (called event above) that contains the name of the property that changed, plus the old and new values of that property.

You can also get a reference to the original object that changed via "name", and then do whatever you'd like through that. In the example above, you can retrieve the systemName, userName (or even other types of status).

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How do I time stamp an output message in my script?

Import the "time" library and then it is easy:

    import time
    print time.strftime("%Y-%m-%d %H:%M:%S"), "Your message or variables here"

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How can I get a script to play a sound?

The jython/ file shows how to play a sound within a script. Briefly, you load a sound into a variable ("snd" in this case), then call "play()" to play it once, etc.

Note that if more than one sound is playing at a time, the program combines them as best it can. Generally, it does a pretty good job.

You can combine the play() call with other logic to play a sound when a Sensor changes, etc. Ron McKinnon provided an example of doing this. It plays a railroad crossing bell when the sensor goes active.

# It listens for changes to a sensor,
# and then plays a sound file when sensor active

import jarray
import jmri

# create the sound object by loading a file
snd = jmri.jmrit.Sound("resources/sounds/Crossing.wav")

class SensndExample(jmri.jmrit.automat.Siglet) :

        # Modify this to define all of your turnouts, sensors and
        # signal heads.
        def defineIO(self):

                # get the sensor
                self.Sen1Sensor = sensors.provideSensor("473")

                 # Register the inputs so setOutput will be called when needed.
                 self.setInputs(jarray.array([self.Sen1Sensor], jmri.NamedBean))


        # setOutput is called when one of the inputs changes, and is
        # responsible for setting the correct output
        # Modify this to do your calculation.
        def setOutput(self):

                if self.Sen1Sensor.knownState==ACTIVE:


# end of class definition

# start one of these up

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How can I run a warrant from within a script?

A Warrant in JMRI is a collection of information sufficient to run an automated train. See the section on setting up warrants here. Get a reference to the warrant you want and run it by executing ("warrants" is a predefined manager reference in jython/

    w = warrants.getWarrant("train 1")

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How do I set a route within a script?

Routes are collections of Turnouts and/or Sensors whose states may be set all at once. See the section on routes here. Get a reference to the route you want and run it by executing:

    r = routes.getRoute("MyRouteName")

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How do I load a xml data file from within a script?


That looks for "filename.xml" in the JMRI program directory, which is not a good place to keep your files. (They tend to get lost or damaged when JMRI is updated). See the next question for a solution to this.

How do I access the JMRI application windows?

Your scripts can change the properties of all the main JMRI windows. They're all jmri.util.JmriJFrame objects, so they have all the various methods of a Swing JFrame. For example, this code snippet

    window = jmri.util.JmriJFrame.getFrameList()[1]

locates the application's main window, and sets its location to the upper left corner of the screen.

The jmri.util.JmriJFrame.getFrameList() call in the first line returns a list of the existing windows. The [0] element of this list is the original splash screen and the [1] element is the main window; after that, they're the various windows in the order they are created. To find a particular one, you can index through the list checking e.g. the window's title with the getTitle() method.

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How do I invoke another script file from a script?


That will look for the file in the top-level JMRI program directory, which might not be what you want. If you want JMRI to search for the file in the default scripts directory (which you can set in preferences), use the slightly more complex form:


The call to jmri.util.FileUtil.getExternalFilename(..) translates the string using JMRI's standard prefixes. The "scripts:" tells JMRI to search in the default scripts directory. You can also use other prefixes, see the documentation.

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How do I communicate between scripts?

All scripts run in the same default namespace, which means that a variable like "x" refers to the same location in all scripts. This allows you to define a procedure, for example, in one script, and use it elsewhere. For example, if a "" file contained:

    def printStatus() :
        print "x is", x
        print "y is", y
        print "z is", z

    x = 0
    y = 0
    z = 0

Once that file has been executed, any later script can invoke the printStatus() routine in the global namespace whenever needed.

You can also share variables, which allows two routines to share information. In the example above, the x, y, and z variables are available to anybody. This can lead to obscure bugs if two different routines are using a variable of the same name, without realizing that they are sharing data with each other. Putting your code into "classes" is a way to avoid that.

Note that scripts imported into another script using import statements are not in the same namespace as other scripts and do not share variables or routines. To share variables from the default namespace with an imported script, you need to explicitly add the shared variable:

    import myImport
    myImport.x = x # make x available to myImport

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How do I find a file in the preferences directory?

You can always specify the complete pathname to a file, e.g. C:\Documents and Files\mine\JMRI\filename.xml or /Users/mine/.jmri/filename.xml. This is not very portable from computer to computer, however, and can become a pain to keep straight.

JMRI provides a routine to convert "portable" names to names your computer will recognize:

     fullname = jmri.util.FileUtil.getExternalFilename("preference:filename.xml")

The "preference:" means to look for that file starting in the preferences directory on the current computer. Other choices are "program:" and "home:", see the documentation.

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