How to subclass a table?

[ftCLI]

Is it possible to subclass a table to add methods?

For example:

OS2.setBoldBit() or name.fromCsv()

Actually I subclassed TTFont and use self[OS/2].setBoldBit() and so on.

[justvanrossum]

You can register a subclass with fontTools.ttLib.ttFont.registerCustomTableClass(); it will override the default class.

[ftCLI]

Thanks for the reply. I'm doing something wrong.

My goal is to add methods to table_O_S_2f_2

For example:

registerCustomTableClass("OS/2", "ftCLI.Lib.OS_2")

class TableOS2(table_O_S_2f_2):

    def customFunction(self):
        print(self.__dict__)

If I run the following:

font = TTFont("font.ttf")
font["OS/2"].customFunction()

I get an attribute error:

AttributeError: 'table_O_S_2f_2' object has no attribute 'customFunction'

[justvanrossum]

Try

registerCustomTableClass("OS/2", "ftCLI.Lib.OS_2", "TableOS2")

If you don't provide the class name as the third argument, it will fall back to "table_O_S_2f_2", which you nicely imported in your module, so effectively it took the built-in class.

[ftCLI]

Thanks indeed! It works fine now.