(gdb) run test-interface.py 
Starting program: /usr/bin/python-dbg test-interface.py
[Thread debugging using libthread_db enabled]
[New Thread 0xb7ea78d0 (LWP 7751)]
python-dbg: ../Objects/stringobject.c:116: PyString_FromString: Assertion `str != ((void *)0)' failed.

Program received signal SIGABRT, Aborted.
[Switching to Thread 0xb7ea78d0 (LWP 7751)]
0xb806a424 in __kernel_vsyscall ()
(gdb) bt
#0  0xb806a424 in __kernel_vsyscall ()
#1  0xb7ed3680 in raise () from /lib/i686/cmov/libc.so.6
#2  0xb7ed6d68 in abort () from /lib/i686/cmov/libc.so.6
#3  0xb7ecc5fe in __assert_fail () from /lib/i686/cmov/libc.so.6
#4  0x080a0af0 in PyString_FromString (str=0x0)
    at ../Objects/stringobject.c:116
#5  0xb7abc5a0 in _wrap_GtkBuildable__proxy_do_add_child (self=0x9e1a830, 
    builder=0x9ed2718, child=0x9e1a530, type=0x0) at gtk.c:114916
#6  0xb7567a2f in IA__gtk_buildable_add_child (buildable=0x9e1a830, 
    builder=0x9ed2718, child=0x9e1a530, type=0x0)
    at /build/buildd-gtk+2.0_2.16.1-2-i386-NWxSfb/gtk+2.0-2.16.1/gtk/gtkbuildable.c:127
#7  0xb756856d in _gtk_builder_add (builder=0x9ed2718, child_info=0x9e1df00)
    at /build/buildd-gtk+2.0_2.16.1-2-i386-NWxSfb/gtk+2.0-2.16.1/gtk/gtkbuilder.c:548
#8  0xb756b981 in end_element (context=0x9c94fb8, 
    element_name=<value optimized out>, user_data=0x9b7ef40, error=0xbfe8797c)
    at /build/buildd-gtk+2.0_2.16.1-2-i386-NWxSfb/gtk+2.0-2.16.1/gtk/gtkbuilderparser.c:1057
#9  0xb7c11d10 in IA__g_markup_parse_context_parse (context=0x9c94fb8, 
    text=0xb7e965b4 "\n<?xml version=\"1.0\"?>\n<interface>\n  <object class=\"TestBindable\" id=\"myobject\">\n    <child>\n      <object class=\"TestBindable\" id=\"myobject2\" />\n    </child>\n  </object>\n</interface>\n", 
---Type <return> to continue, or q <return> to quit---
    text_len=184, error=0xbfe87a08)
    at /build/buildd-glib2.0_2.20.1-2-i386-hGzT8z/glib2.0-2.20.1/glib/gmarkup.c:1712
#10 0xb756aa5e in _gtk_builder_parser_parse_buffer (builder=0x9ed2718, 
    filename=0xb77cb1a7 "<input>", 
    buffer=0xb7e965b4 "\n<?xml version=\"1.0\"?>\n<interface>\n  <object class=\"TestBindable\" id=\"myobject\">\n    <child>\n      <object class=\"TestBindable\" id=\"myobject2\" />\n    </child>\n  </object>\n</interface>\n", 
    length=4294967295, requested_objs=0x0, error=0xbfe87a08)
    at /build/buildd-gtk+2.0_2.16.1-2-i386-NWxSfb/gtk+2.0-2.16.1/gtk/gtkbuilderparser.c:1188
#11 0xb756a0e6 in IA__gtk_builder_add_from_string (builder=0x9ed2718, 
    buffer=0xb7e965b4 "\n<?xml version=\"1.0\"?>\n<interface>\n  <object class=\"TestBindable\" id=\"myobject\">\n    <child>\n      <object class=\"TestBindable\" id=\"myobject2\" />\n    </child>\n  </object>\n</interface>\n", 
    length=4294967295, error=0xbfe87a3c)
    at /build/buildd-gtk+2.0_2.16.1-2-i386-NWxSfb/gtk+2.0-2.16.1/gtk/gtkbuilder.c:784
