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.

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

  • Build the machida 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 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. For example, if you have followed the directions for setting up the tutorial then the Wallaroo Python module is in $HOME/wallaroo-tutorial/wallaroo-0.5.3/machida/wallaroo.py and the "Celsius to Fahrenheit" application module is in $HOME/wallaroo-tutorial/wallaroo-0.5.3/examples/python/celsius/celsius.py, so you would export PYTHONPATH like this:

export PYTHONPATH="$PYTHONPATH:$HOME/wallaroo-tutorial/wallaroo-0.5.3/machida/lib:$HOME/wallaroo-tutorial/wallaroo-0.5.3/examples/python/celsius"

If you are working your way through the tutorial you might find it easier to set up PYTHONPATH to use whatever directory you are in as the search path so that you can run the application that is the current directory. To do this, you would export PYTHONPATH like this:

export PYTHONPATH="$PYTHONPATH:$HOME/wallaroo-tutorial/wallaroo-0.5.3/machida/lib:."

If you chose to do this while working through the tutorial, you might also find it useful to add the path to the machida executable to your PATH, which can be done like this:

export PATH="$PATH:$HOME/wallaroo-tutorial/wallaroo-0.5.3/machida/build"

Next Steps

To try running an example, go to the Reverse 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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