Running A Wallaroo Python Application

Setting Up Wallaroo

You should have already completed the setup instructions in the "Setting Up Your Environment for Wallaroo" section of this guide.

Running the Application

Wallaroo uses an embedded Python runtime wrapped with a C API around it that lets Wallaroo execute Python code and read Python variables. So when machida --application-module my_application is run, machida (the binary we previously compiled), loads up the my_application.py module inside of its embedded Python runtime and executes its application_setup() function to retrieve the application topology it needs to construct in order to run the application. machida3 does the same, but with an embedded Python 3 runtime instead of Python 2.7.

Generally, in order to build a Wallaroo Python application, the following steps should be followed:

  • Build the machida or machida3 binary (this only needs to be done once)
  • import wallaroo in the Python application's .py file
  • Create classes that provide the correct Wallaroo Python interfaces (more on this later)
  • Define an application_setup function that uses the ApplicationBuilder from the wallaroo module to construct the application topology.
  • Run machida or machida3 with the application module as the --application-module argument

Once loaded, Wallaroo executes application_setup(), constructs the appropriate topology, and enters a ready state where it awaits incoming data to process.

A Note About PYTHONPATH

Machida uses the PYTHONPATH environment variable to find modules that are imported by the application. You will have at least two modules in your PYTHONPATH: the application module and the wallaroo module. If you have installed Wallaroo as instructed and follow the Starting a new shell for Wallaroo instructions each time you start a new shell, the walalroo module and any application modules in your current directory will be automatically added to the PYTHONPATH.

If the Python module you want is in a different directory than your current, like: $HOME/wallaroo-tutorial/wallaroo-0.6.0/examples/python/alerts_stateless/alerts.py, in order to use the module you would export the PYTHONPATH like this:

export PYTHONPATH="$HOME/wallaroo-tutorial/wallaroo-0.6.0/examples/python/alerts_stateless:$PYTHONPATH"

Next Steps

To try running an example, go to the Alerts example application and follow its instructions.

To learn how to write your own Wallaroo Python application, continue to Writing Your Own Application

To find out more detail on the command line arguments and other aspects of running Wallaroo application, see the Running Wallaroo section.

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