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Creating and invoking Python actions

The process of creating Python actions is similar to that of other actions. The following sections guide you through creating and invoking a single Python action, and demonstrate how to bundle multiple Python files and third party dependencies.

An example action Python action is simply a top-level function. For example, create a file called hello.py with the following source code:

def main(args):
    name = args.get("name", "stranger")
    greeting = "Hello " + name + "!"
    print(greeting)
    return {"greeting": greeting}

An action supports not only a JSON object but also a JSON array as a return value.

It would be a simple example that uses an array as a return value:

def main(args):
    return ["a", "b"]

You can also create a sequence action with actions accepting an array param and returning an array result.

You can easily figure out the parameters with the following example:

def main(args):
    return args

Python actions always consume a dictionary and produce a dictionary. The entry method for the action is main by default but may be specified explicitly when creating the action with the nuv CLI using --main, as with any other action type.

You can create an OpenWhisk and Nuvolaris action called helloPython from this function as follows:

nuv action create helloPython hello.py

The CLI automatically infers the type of the action from the source file extension. For .py source files, the action runs using a Python 3.6 runtime.

Action invocation is the same for Python actions as it is for any other actions:

nuv action invoke --result helloPython --param name World
  {
      "greeting": "Hello World!"
  }

Find out more about parameters in the Working with parameters section.

Packaging Python actions in zip files

You can package a Python action and dependent modules in a zip file. The filename of the source file containing the entry point (e.g., main) must be main.py. For example, to create an action with a helper module called helper.py, first create an archive containing your source files:

zip -r helloPython.zip __main__.py helper.py

and then create the action:

nuv action create helloPython --kind python:3 helloPython.zip

Packaging Python actions with a virtual environment in zip files

Another way of packaging Python dependencies is using a virtual environment (virtualenv). This allows you to link additional packages that may be installed via pip for example. To ensure compatibility with the OpenWhisk and Nuvolaris container, package installations inside a virtualenv must be done in the target environment. So the docker image openwhisk/python3action should be used to create a virtualenv directory for your action.

As with basic zip file support, the name of the source file containing the main entry point must be main.py. In addition, the virtualenv directory must be named virtualenv. Below is an example scenario for installing dependencies, packaging them in a virtualenv, and creating a compatible OpenWhisk and Nuvolaris action.

  1. Given a requirements.txt file that contains the pip modules and versions to install, run the following to install the dependencies and create a virtualenv using a compatible Docker image:

docker run --rm -v "$PWD:/tmp" openwhisk/python3action bash \
  -c "cd tmp && virtualenv virtualenv && source virtualenv/bin/activate && pip install -r requirements.txt"

  1. Archive the virtualenv directory and any additional Python files:

zip -r helloPython.zip virtualenv __main__.py

  1. Create the action:

nuv action create helloPython --kind python:3 helloPython.zip

Python 3 actions

Python 3 actions are executed using Python 3.6.1. This is the default runtime for Python actions, unless you specify the --kind flag when creating or updating an action. The following packages are available for use by Python actions, in addition to the Python 3.6 standard libraries.

  • aiohttp v1.3.3

  • appdirs v1.4.3

  • asn1crypto v0.21.1

  • async-timeout v1.2.0

  • attrs v16.3.0

  • beautifulsoup4 v4.5.1

  • cffi v1.9.1

  • chardet v2.3.0

  • click v6.7

  • cryptography v1.8.1

  • cssselect v1.0.1

  • Flask v0.12

  • gevent v1.2.1

  • greenlet v0.4.12

  • httplib2 v0.9.2

  • idna v2.5

  • itsdangerous v0.24

  • Jinja2 v2.9.5

  • kafka-python v1.3.1

  • lxml v3.6.4

  • MarkupSafe v1.0

  • multidict v2.1.4

  • packaging v16.8

  • parsel v1.1.0

  • pyasn1 v0.2.3

  • pyasn1-modules v0.0.8

  • pycparser v2.17

  • PyDispatcher v2.0.5

  • pyOpenSSL v16.2.0

  • pyparsing v2.2.0

  • python-dateutil v2.5.3

  • queuelib v1.4.2

  • requests v2.11.1

  • Scrapy v1.1.2

  • service-identity v16.0.0

  • simplejson v3.8.2

  • six v1.10.0

  • Twisted v16.4.0

  • w3lib v1.17.0

  • Werkzeug v0.12

  • yarl v0.9.8

  • zope.interface v4.3.3