Walaroo and Virtualenv

We recommend using virtualenv to handle your application's dependencies.

While not required to run Wallaroo applications, virtualenv will ensure that your application and development environment are isolated from the rest of your Python installation(s) on your computer. In addition, virtualenv will ensure that Machida uses the correct version of Python if you have multiple versions installed on your computer.

Installing Virtualenv

Follow the instructions on the virtualenv website.

Setting up Virtualenv for your Application

To create a virtualenv for your application, run the following command

virtualenv --python=python2 ENV

This will create a directory named ENV and set up all of the scripts and dependencies required to run an isolated Python2 virtual environment, located in ENV.

Import Errors when Loading your Application

If you have more than one Python version installed, virtualenv may set up the import paths incorrectly, or an alias may result in the wrong Python version being run. In that case, you may encounter errors such as

Traceback (most recent call last):
  File "wallaroo/examples/python/celsius/celsius.py", line 18, in <module>
    import wallaroo
  File "wallaroo/machida/wallaroo.py", line 16, in <module>
    import argparse
  File "/usr/local/Cellar/python/2.7.14/Frameworks/Python.framework/Versions/2.7/lib/python2.7/argparse.py", line 86, in <module>
    import copy as _copy
  File "/usr/local/Cellar/python/2.7.14/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 52, in <module>
    import weakref
  File "/usr/local/Cellar/python/2.7.14/Frameworks/Python.framework/Versions/2.7/lib/python2.7/weakref.py", line 14, in <module>
    from _weakref import (
ImportError: cannot import name _remove_dead_weakref
Could not load module 'celsius'

In order to work correctly, virtualenv needs to be set up with the correct Python path. To do this, use which to get the absolute path of your intended Python version:

virtualenv --python=`which python` ENV

If you use a different Python, such as python2 or python2.7, then substitute that into the which command:

virtualenv --python=`which python2.7` ENV

Cleaning up a Virtualenv

To clean up or remove an installed virtualenv, all you need to do is delete the directory you created.

For the ENV virtualenv set up above, the following will remove it entirely:

rm -fr ENV

Using Virtualenv

To use the virtualenv, activate it in your shell. In the bash shell, this command is

$ source ENV/bin/activate
(env) $

If this command does not work for your specific shell, please refer to the virtualenv userguide.

Now, when you run python or pip, it will be using the ones set up in the virtual environment, and any new packages and dependencies will be installed within the ENV path.

To install new modules using pip, run pip within an activated virtualenv:

(env) $ pip install ujson

To exit the virtualenv, use the deactivate command.

Running a Wallaroo Application with Virtualenv

To run a Wallaroo application with virtualenv, run it within an activated shell:

source ENV/bin/activate
export PYTHONPATH="$HOME/wallaroo-tutorial/wallaroo/machida:$HOME/wallaroo-tutorial/wallaroo/examples/python/celsius"
$HOME/wallaroo-tutorial/wallaroo/machida/build/machida --application-module celsius \
  --in 127.0.0.1:7000 --out 127.0.0.1:5555 --metrics 127.0.0.1:5001 \
  --control 127.0.0.1:6000 --data 127.0.0.1:6001 --name worker-name \
  --external 127.0.0.1:5050 --cluster-initializer --ponythreads=1 \
  --ponynoblock

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