[pygtk] selectable paper size in page setup dialog

[golnaz nilieh]

I created a PrintOperation and set A4 size for its default paper size,
using code below:

        self.operation = gtk.PrintOperation()
        self.page_setup = gtk.PageSetup()
        self.page_setup.set_paper_size_and_default_margins(gtk.PaperSize(gtk.PAPER_NAME_A4))
        self.operation.set_default_page_setup(self.page_setup)

When the print dialog opens, It shows A4 size as the default paper
size, but it is read-only.
How can I change the code so that users can select other paper-sizes, too?

Maybe helpful: I use pygtk 2.17 on ubuntu.