Fiddling with the Bundled Examples

The previous tutorials have shown how to develop various types of Tangelo applications, but you might also want to simply fiddle around with the example applications that come bundled with Tangelo. Since the bundled examples are treated in a somewhat special manner by Tangelo, this tutorial explains how you can make a copy of the example applications, set them up with a Tangelo configuration file, and then experiment and see the results yourself.

The examples can be viewed at http://localhost:8080 by launching Tangelo in example mode:

tangelo --examples

The index page contains links to different examples, each of which is served as the web content of one plugin or another. For example, http://localhost:8080/plugin/vis/examples/barchart/ serves an example of the barchart that is part of the vis plugin.

The Example Web Applications

The example web applications are bundled in the Tangelo Python package with the following directory structure:


The file tangelo.ico is served by Tangelo statically as the default favicon, while the web directory contains the example site’s front page (including the Tangelo Sunrise, and the menu of links to the individual examples). The examples themselves are contained within the plugin directory. As an example, the directory for the Bokeh plugin looks like this:


This plugin contains a Python component and a clientside component, as well as the Iris example application, which demonstrates how the pieces fit together (for information about how plugins work, see Tangelo Plugins). The web application content in the iris directory would be a good place to play around to discover for yourself how this plugin works.

Therefore, we will want to make a private copy of the web and plugin directories in order to experiment with the contents of the example web applications.

Making a Copy

To actually play with the examples, we’d like to set up our own sandbox, copy these materials into it, configure Tangelo to run with the appropriate plugins, and finally serve our own version of the example applications.

Step 1: Create a Sandbox

The examples are bundled as package data with the Tangelo Python package, meaning they will be found within the tangelo/pkgdata subdirectory of the site-packages directory of the Python installation that contains Tangelo. On a typical Linux Python installation, this directory might be /usr/lib/python2.7/site-packages/tangelo/pkgdata. Because different Python setups may behave differently with respect to where such files are kept, Tangelo includes a program tangelo-pkgdata that simply reports the full path to the pkgdata directory. Using this program, the following sequence of shell commands will create an area where we can safely modify and otherwise experiment with the examples:

$ cd ~
$ mkdir tangelo-examples
$ cd tangelo-examples
$ cp -r `tangelo-pkgdata` .

(Enclosing a command in backticks causes the shell to run the enclosed program and substitute its output in the original command. You can also run tangelo-pkgdata manually, inspect the output, and copy it into your own manual shell command as well.)

Step 2: Configure the Plugins

We will want to have Tangelo serve the web directory, while loading the appropriate plugins from the plugin directory. For the latter, we will need a configuration file to declare the plugins:

This very simple configuration simply names the plugins we need, together with relative paths stating where the plugins can be found. Create a file config.yaml (in the tangelo-examples directory) and copy the configuration into it.

Step 3: Launch Tangelo

Now that we have web materials, plugins, and a configuration, we just need to start Tangelo:

$ tangelo --root web --config config.yaml

Tangelo should begin serving the example site at http://localhost:8080 (if you get an error about port 8080 not being free, try again with the --port option to select a different port).

Step 4: Fiddle!

Now you can go into the various web subdirectories of the plugin paths, make changes, and observe them live. If you find things don’t update as expected, you can try restarting the server (certain features of plugins can only be instantiated when Tangelo first starts up).

Try changing the data values in the mapping plugin examples, or changing how some of the web services retrieve, process, or format their output data. With a safe, hands-on approach, you can learn a lot about how Tangelo operates.