# Overview of OpenMDAO Plugin Development¶

Plugins provide a way to extend the functionality of OpenMDAO without modifying the framework itself. This is possible because a plugin implements a particular interface that the framework knows how to interact with. This section describes the types of plugins available to extend the functionality of OpenMDAO and explains how to build them and how to make them usable by the framework.

The rest of this document assumes that you have already installed OpenMDAO. If you haven’t, learn how to do that here.

Note

If you intend to develop a plugin on Windows that requires compilation, you will need to have the necessary compiler(s) installed on your system. See the Developer Guide installation instructions for Windows for help installing Visual C++ 2008 and mingw32.

## How Do I Put My Plugin into OpenMDAO?¶

Plugins within OpenMDAO are just Python classes that provide an expected interface, so as long as your class provides the necessary interface and can be imported into your Python script, you’ll be able to use it as a plugin. But what if an OpenMDAO user wants to obtain a listing of all of the plugins that are available in the environment? To allow that to happen, a plugin developer must provide metadata that specifies the name, plugin interface, and location within its package for each plugin that is intended to be discoverable by the framework. This metadata is in the form of an entry point. An entry point is just a mapping of a name to some Python object, in our case a class, that exists within a distribution. Each entry point must be a member of an entry point group. An application can look at the entry point groups that are defined to determine if any applicable plugins exist within a given distribution. In the case of OpenMDAO, we look for entry point group names that correspond to the types of plugin interfaces that we support.

## Types of Plugin Interfaces¶

OpenMDAO supports a number of different plugin interfaces. Each one maps to a different entry point group. The following table shows the mapping of each entry point group to the purpose within the framework of plugins in that group:

Entry Point Group Purpose
openmdao.component To add custom computations to an OpenMDAO model
openmdao.variable To add custom data object to pass between components
openmdao.driver To add custom iterative executive (optimizer, solver, design space explorer) to an OpenMDAO model
openmdao.case_iterator To add custom supplier of Cases
openmdao.resource_allocator To add custom handling of allocation of computing resources

Note

The entry point group names look like they could be the names of Python modules or packages, but they’re not. They’re just strings that a plugin developer uses to indicate to the framework that his plugin supports a particular plugin interface.

The framework also provides a base class corresponding to most plugin interfaces to make it easier for developers to create new plugins by simply inheriting from the base class and modifying a small number of methods and/or attributes.

The table below shows each base class and the entry point group that it belongs to:

Base Class Entry Point Group
openmdao.main.api.Component openmdao.component
openmdao.main.api.Variable openmdao.variable
openmdao.main.api.Driver openmdao.driver
openmdao.main.resource.ResourceAllocator openmdao.resource_allocator

Note that every plugin in openmdao.driver is also assumed to be a member of openmdao.component since Driver inherits from Component.

### Plugin Development Tools¶

There is a script called plugin available to simplify the process of developing and installing plugin distributions. The table below shows each subcommand of plugin with a brief description of its purpose. All of the subcommands are described in more detail in Building a Component Plugin.

Command Purpose
plugin build_docs To build the html docs for the plugin
plugin docs To view the html docs for the plugin
plugin install To install the plugin into the active environment
plugin list To list installed or available plugins
plugin makedist To create a source distribution containing the plugin
plugin quickstart To create the directory structure needed to build the plugin distribution

### Defining Entry Points¶

The good news is that if you use the plugin makedist tool to package your plugin, the setup.py file with all necessary entry points will be created for you automatically. The bad news is that there are some cases where plugin makedist cannot be used, so the entry points must be defined manually. The rest of this section describes how to add entry points and other metadata to a distribution manually.

Entry points are defined within the setup.py file that is used to build the distribution. The following code snippet shows a setup.py file that defines an entry point for an OpenMDAO component plugin called SimpleAdder in a distribution called simple_adder:

from setuptools import setup, find_packages

setup(
version='1.0',
packages=find_packages(),
install_requires=['openmdao.lib'],
entry_points={
}
)


The example above shows that an entry point named simple_adder.SimpleAdder that maps to the SimpleAdder class within the simple_adder.py module is a member of the openmdao.component entry point group. This tells OpenMDAO that the SimpleAdder plugin is an OpenMDAO Component. The list of entry point groups that OpenMDAO recognizes is the same as the list of plugin types shown in the table above.

Note

You should always use the full module dotted name as the name of your entry point to be consistent with other OpenMDAO plugins.

Once you have your setup.py file and your plugin class is complete, you’re ready to build a distribution. If you’re not able to use plugin makedist for some reason, you can build your distribution by executing your setup.py file in the following way:

python setup.py sdist -d .

This will create a source distribution and place it in the current directory. If your distribution is named simple_adder, for example, the source distribution will be named simple_adder-1.0.tar.gz, or possibly simple_adder-1.0.zip on Windows. The version of the packaged distribution is 1.0 as was specified in the setup.py file.

### Installing an OpenMDAO Plugin¶

If you run plugin install from the top directory of your plugin distribution, it will install your plugin as a develop egg, meaning that it places a link to your distribution on the Python path so that you can make changes to your plugin and test it in the environment without having to keep reinstalling it.

If you have a distrbution tar or zip file, created either by using plugin makedist or by running setup.py directly, you can install your plugin into an OpenMDAO virtual environment by running plugin install and passing it the name of the file, for example:

plugin install myplugin-0.5.tar.gz

which will install the distribution into the site-packages directory of your OpenMDAO virtual environment.

Finally, if you want to install a plugin distribution from a remote server, it would look like:

plugin install [-f <find_links_url>] <distrib_requirement>

where find_links_url is the url for a find_links server and distrib_reqirement is a requirement string in the same form as you would pass to easy_install or pip. For example, myplugin, myplugin==0.5, and myplugin>=0.3 are all valid requirement strings. If there is no version specifier in the distrib_requirement, then the latest version compatible with the current platform will be installed.

### Making Your Plugin Available to Others¶

You can make your plugin available to others in a number of ways, from simply emailing your distribution to others or giving it to them on a thumb drive, CD, etc., or placing your distribution on a file server that they can access. As mentioned above, plugin install allows you to download and install Python distributions from remote web servers. For example, if there were a distribution called MyDist on the openmdao.org server and you wanted to grab the newest version of it, you could plugin install it into your activated OpenMDAO virtual environment as follows:

plugin install -f http://openmdao.org/dists MyDist

If you want to distribute your plugin to the whole world but don’t happen to have your own public server, you can put your plugin up on the Python Package Index (PyPI), which is also known as the Cheeseshop. PyPI is the default package index for plugin install, so the command

plugin install MyDist