Packing objects from external packages

Sometimes it may be necessary to pack objects that are defined by the Python standard library or a third-party package such as Django. In this case, adding a telepath_pack method as described earlier is not an option, since the class definition exists outside of your own code. To accommodate this, telepath allows you to define the packing logic in an Adapter object, and register this so that it is used whenever an object of the given type is encountered.

For example, suppose we want to be able to pack datetime.time instances. This can be done as follows:

import datetime
from telepath import Adapter, register


class TimeAdapter(Adapter):
    def pack(self, obj, context):
        context.add_media(js='datetime.js')
        return ('datetime.Time', [obj.hour, obj.minute, obj.second])


register(TimeAdapter(), datetime.time)

The pack method here works in the same way as a telepath_pack method on the class itself, except that the object is passed as an argument rather than operating on self. The resulting TimeAdapter object is then passed to register to be used for datetime.time instances.

On the JavaScript side, the datetime.Time constructor can then be defined and registered in the same way as before. In datetime.js:

class Time {
    constructor(hour, minute, second) {
        this.hour = hour;
        this.minute = minute;
        this.second = second;
    }

    toString() {
        return (
            this.hour.toString().padStart(2, '0')
            + ':' + this.minute.toString().padStart(2, '0')
            + ':' + this.second.toString().padStart(2, '0')
        );
    }
}
window.telepath.register('datetime.Time', Time);