Multi Image Docker Spawner

[nils-werner]

This is less a bug, and also not quite a pull request, but more an idea or a recipe: You can allow users to chose the docker image they are using upon starting their server by using something like the following

from dockerspawner import SystemUserSpawner

class MultiDockerImageSpawner(SystemUserSpawner):
    images = {
        'SciPy': 'jupyter/scipy-notebook:0f73f7488fa0',
        'Tensorflow': 'jupyter/tensorflow-notebook:59904dd7776a',
        'R': 'jupyter/r-notebook:59904dd7776a',
    }
    def _options_form_default(self):
        outval = """
        <label for="image">Docker Image</label>
        <select name="image">
        """
        for name, image in self.images.items():
            outval += "<option value=\"%s\">%s (%s)</option>" % (name, name, image)

        outval += """
        </select>
        """
        return outval

    def options_from_form(self, formdata):
        options = {}
        options['image'] = formdata.get('image', ['SciPy'])[0]
        self.image = self.images[options['image']]
        return options

@minrk what do you think about this? would you be interested in wrapping this up in a class that goes in the codebase?

[minrk]

This is very much like what I drafted in #219. I should finish that up!

[nils-werner]

Ah, didn't see that, sorry :-)