Writing Your Own Script

Author: Kurt Shuster

Custom ParlAI Script

If you have accustomed yourself with the parlai command and would like to write your own ParlAI-based script, this tutorial is meant for you. Writing and using a script today in ParlAI is a smooth experience, thanks to recent work in standardizing scripts across the repository.


The ParlaiScript class is the abstract class which all ParlAI scripts subclass. A script in ParlAI must define two methods:


The setup_args function returns a ParlaiParser with relevant command line args specified. As an example, the TrainModel script adds several arguments required for training a model (number of train epochs, validation statistics, etc.).


This is where you run whatever it is you’re attempting to run in your script. In this function you’ll have access to self.opt, which is an Opt dictionary with the appropriate options filled in from setup_args.

Suppose we want to write a script that loads a file and prints its length. We may start with the following signature:

from parlai.core.params import ParlaiParser
from parlai.core.script import ParlaiScript

class LengthScript(ParlaiScript):

    def setup_args(cls):
        parser = ParlaiParser(True, True)
            help="File to analyze in this script"
        return parser

    def run(self):
        with open(self.opt["length_filepath"]) as f:
            file_content = f.read()
        print(f"Your file has {len(file_content)} characters!")
        return len(file_content)

Registering a Script

After writing your script, you can “register” your script to be picked up by the parlai global command. This can be achieved via importing the register_script function, and wrapping your script with the decorator, e.g. in the following way:

from parlai.core.script import ParlaiScript, register_script

@register_script("length_script", aliases=["length"])
class LengthScript(ParlaiScript):

Running a script

Now that you’ve written and registered your script, it’s time to run it!

There are three ways you can now run your script with appropriate options:

Command Line

Now that you’ve registered your script, you can run it on the command line:

$ parlai length_script --length-filepath file_to_measure.txt

Import and Run with Args

You can also import your script into another file and run it via its .main function:

from my_script.module import LengthScript

if __name__ == "__main__":
    LengthScript.main(['--length-filepath', 'file_to_measure.txt'])

Import and Run with Kwargs

Finally, rather than specifying args as if from the command line, you can run scripts via passing in keyword arguments:

from my_script.module import LengthScript

if __name__ == "__main__":