Trouble Trying To Dynamically Add Methods To Python Class (i.e. Django-tables2 'table')

So for a Django project, I would really like to be able to generate and display tables (not based on querysets) dynamically without needing to know the contents or schema beforehan

Solution 1:

You're on the right track here, but instead of creating a barebones class and adding attributes to it, you should use the type() built-in function. The reason it's not working the way you're trying, is because the metaclass has already done its work.

Using type() allows you to construct a new class with your own attributes, while setting the base class. Meaning - you get to describe the fields you want as a blueprint to your class, allowing the Tables metaclass to take over after your definition.

Here's an example of using type() with django. I've used this myself for my own project (with some slight variations) but it should give you a nice place to start from, considering you're already almost there.

defdefine_table(columns):
    attrs = dict((c, tables.Column()) for c in columns)
    klass = type('DynamicTable', (tables.Table,), attrs)
    return klass

Solution 2:

You're confusing the __new__ of a "regular" class with the __new__ of a metaclass. As you note, Table relies on __new__ method on its metaclass. The metaclass is indeed invoked when the class is defined. The class is itself an instance of the metaclass, so defining the class is instantiating the metaclass. (In this case, Table is an instance of DeclarativeColumnMetaClass.) So by the time the class is define, it's too late.

One possible solution is to write a Table subclass that has some method refreshColumns or the like. You could adapt the code from DeclarativeColumnMetaclass.__new__ to essentially make refreshColumns do the same magic again. Then you could call refreshColumns() on your new class.