JMRI is...


Information on writing scripts to control JMRI in more detail:

Python and Jython (General Info)

JMRI scripts are in Jython, a version of Python, a popular general-purpose computer language


JMRI provides powerful tools for working with your layout.

Layout Automation

JMRI can be used to automate parts of your layout, from simply controlling a crossing gate to running trains in the background.

JMRI: Scripting "How To..."

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

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 "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 create 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 created within a script (all can also be accessed, of course). A simple line of code typed into the Script Entry window is all it takes:

	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. Variables within the object can then 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

System names versus user names

System names for sensors, turnouts, lights and others, are connection specific. A LocoNet sensor name begins with "LS" while a CMRI sensor begins with "CS" and an internal sensor with "IS". "provide" methods check the prefix of the passed string to determine if it matches a defined connection or internal. If so, and the rest of the name is valid, the sensor is created. If a match does not exist, it assigns the prefix for the first connection in the currently open connection list.

Example: If your connections are LocoNet and CMRI, a provideSensor request without a prefix of LS, CS or IS, will be assigned LS. If the name value is not one to four numeric digits (a LocoNet requirement), you get a bad format error. Memories are only internal, so provideMemory uses "IM" as the default prefix.

User names are set after input and outputs are created. They can be any character string you want. You can use user name or system name in scripts and Logix. The use of user names is recommended for these purposes if there is the possibility that you will be changing your control system in which case system names will be changing as well.

Click for more information on Names and Naming.

Alternative syntax in Python

The Python language provides alternative ways of addressing objects and methods. It is not the purpose of this FAQ to explain all of these, but it is worth noting that the above examples could have been written as:


No assignment operator (=) is necessary as the "set" methods do that work. Use whichever syntax you prefer, although it is a good practice is to be consistent for future readability.

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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 below 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 do I load a panel 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 now 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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