Nemo Plugin System

Since flask-capitains-nemo 1.0.0, plugins are a reality. They bring a much easy way to stack new functionalities in Nemo and provide large reusability and modularity to everyone.


Nemo Plugins are quite close in design to the Nemo object but differ in a major way : they do not have any Flask Blueprint instance and are not aware directly of the flask object. They only serve as a simple and efficient way to plugin in Nemo a set of resources, from routes to assets as well as filters.

The way Nemo deals with plugins is based on a stack design. Each plugin is inserted one after the other and they take effect this way. The last plugin routes for the main route / is always the one showed up, as it is for assets and templates namespaces.

What are plugins

What can plugin do

  • It can add assets (javascript, css or static files such as images)
  • It can provide new templates to theme Nemo
  • It can add new routes on top of the existing routes
  • It can remove original routes, and bring new one
  • It can bring new filters
  • It can add new informations to what is passed to the template through their pluginRender function

How plugin are registered

At the creation of the Blueprint in Nemo, Nemo runs a function which does the following in said order:

  • Clear routes first if asked by one plugin
  • Clear assets if asked by one plugin and replace by the last registered plugin STATIC_FOLDER
  • Register each plugin
    • Append plugin routes to registered routes
    • Append plugin filters to registered filters
    • Append templates directory to given namespaces
    • Append assets (CSS, JS, statics) to given resources
    • Append render view (if exists) to Nemo.render stack

Inserting a plugin in a Nemo instance

# We import Flask and Nemo
from flask import Flask
from flask_nemo import Nemo
# For this demo, we use the plugin prototype which does not include anything special
from flask_nemo.plugin import PluginPrototype
from MyCapytain.resolvers.cts.api import HttpCtsResolver
from MyCapytain.retrievers.cts5 import HttpCtsRetriever

# We set up a resolver which communicates with an API available in Leipzig
resolver = HttpCtsResolver(HttpCtsRetriever(""))

# Initiate the app
app = Flask(__name__)
# We initiate the plugins
proto_plug = PluginPrototype()
# We insert the plugin into Nemo while setting up Nemo
nemo = Nemo(

Writing a plugin

The major properties of plugins are - and should be - class variables and copied during initiation to ensure a strong structure. There is list of core class constants which are defined below. It is recommanded to use PluginPrototype class as your parent object :

Assets providing

There is three class variables (JS, STATICS and CSS) related to register new UI resources on to the Nemo instance.

  • Remote resources (http://, https://, //) will be simply sent to the templates css and js variables so that it can be called from here (such as <script src="//"></script>)
  • Local resources (such as /directory/assets/css/stuff.css) will be made available through Nemo secondary assets route and fed to the templates as local resources.

Adding routes, adding/overwriting templates and filters

The ROUTES and TEMPLATES class variables work the same way as the Nemo one : they will be registered on to the Nemo instance on top of the existing routes.

  • Routes of plugins stack up and overwrite themselves if they are not namespaced (See namespacing argument in pluginInit).
  • Templates can provide new templates for the main:: namespace as well as new templates for any other namespace (cf. templateOrder)
  • The clear route function will erase original provided routes of Nemo if set to True before registering other plugins (See register_plugins())
  • Filters works like Nemo filters. They can be namespaced using the namespacing argument.
  • Routes can be cached by providing their name in CACHED

Various other core parameters : render, clear assets and static folder

  • Plugin.render() view brings a new stack of values to the variables that are sent to the template (cf. renderWorkflow). HAS_AUGMENT_RENDER is the class variable that when set to True will make Nemo aware of the existence of the function.
  • CLEAR_ASSETS clears registered defaults assets in Nemo assets dictionary.
  • STATIC_FOLDER overwrites original Nemo static folder. It is recommended not to make too much use of it except if you do not need any of the original Nemo assets.