extensions 0.4

How to define a plugin

A plugin can be any callable object . It has to be registered through the extensions registry.

For example, let’s take a simple function that calculates the average of some numbers, and let’s save it into a file called extensions.py in a package called myapp:

def average(*args):
     return sum(args) / len(args)

This function can be registered in the plugin system using the register function. Plugins have a name and belong to a group. For our example, the group can be myapp.operator and the name average:

from extensions import register

# usage : register(group, name, location)
register('myapp.operator', 'average', 'myapp.extensions:average')

The third parameter gives the location of the callable, with the form module_name:attrs, where module_name is the full name of the module, and attrs the attributes in the module.

Notice that the group name includes the name of the package, which is a good practice to avoid collisions since the group names are global to all applications that use extensions.

[myapp.operator]

average = myapp.extensions:average

from extensions import register_file

register_file('operators.cfg')

How to use a plugin

from extensions import get

for plugin in get(group='myapp.operator'):
    print plugin.name

for plugin in get(group='myapp.operator', name='average'):
     print plugin.name

from itertools import islice

for plugin in islice(get(), 5):
    print plugin.name

# let's get the plugin `average` of the group `myapp.operator`
plugin = get(group='myapp.operator', name='average').next()

# let's load it
func = plugin.load()

# let's use it now
average = func(1, 2, 3)

Distribute your plugins

If you want to distribute your plugins, you just have to import the module that registers the plugins into your setup.py file:

from distutils.core import setup
from myapp import plugins  # registers the plugins

setup(name='myapp', version='1.0'
      packages=['myapp'])

This will register the plugins when the package is installed by creating a special file called PLUGINS into the .egg-info directory created when your package is installed.

Compatibility with setuptools entry points

extensions is fully compatible with setuptools entry points. So you can iterate and use entry points defined in third-party applications that are installed in your Python.

If you want to iterate through setuptools entry points, use the consume_entry_points option when you call the get function:

plugins = get(consume_entry_points=True)

This will iterate over extensions plugins and setuptools entry points.

References