Thanks! I merged with some small modifcations and pyflake fixes into lp:~mvo/software-center/packagekit-backend. I moved the backend code into the gtk3 version of s-c as it seems like
there are just too many issues mixing the old gtk2/pygtk and pygi code. This should be fine
as the gtk3 version is actually pretty good now.

I have a questions:
- in line 578 "package" is assigned but not used, what is this needef for? 

I like that test_pkginfo.py now tests both implementations! However when I run it it segfaults on my up-to-date oneiric box:
#0  0x000000000045f0b5 in insertdict (mp=0x4cd8c00, key='firefox', 
    hash=2252328806807869700, value=<unknown at remote 0x7fffffff3850>)
    at ../Objects/dictobject.c:526
#1  0x0000000000460496 in PyDict_SetItem (op={}, key=<optimized out>, 
    value=<optimized out>) at ../Objects/dictobject.c:775
#2  0x00000000004b74b5 in PyEval_EvalFrameEx (f=<optimized out>, 
    throwflag=<optimized out>) at ../Python/ceval.c:1706
#3  0x00000000004bcced in PyEval_EvalCodeEx (co=0xd2d730, 
    globals=<optimized out>, locals=<optimized out>, args=<optimized out>, 
    argcount=<optimized out>, kws=<optimized out>, kwcount=0, defs=0xd324e8, 
    defcount=2, closure=0x0) at ../Python/ceval.c:3253
#4  0x00000000004b69db in fast_function (nk=<optimized out>, na=2, 
    n=<optimized out>, pp_stack=0x7fffffffb9a0, func=
    <function at remote 0xe8a1b8>) at ../Python/ceval.c:4117
#5  call_function (oparg=<optimized out>, pp_stack=0x7fffffffb9a0)
    at ../Python/ceval.c:4042
#6  PyEval_EvalFrameEx (f=<optimized out>, throwflag=<optimized out>)
    at ../Python/ceval.c:2666
#7  0x00000000004b6cf7 in fast_function (nk=<optimized out>, 
    na=<optimized out>, n=<optimized out>, pp_stack=0x7fffffffbae0, func=
    <function at remote 0xe1bf50>) at ../Python/ceval.c:4107
#8  call_function (oparg=<optimized out>, pp_stack=0x7fffffffbae0)
    at ../Python/ceval.c:4042
#9  PyEval_EvalFrameEx (f=<optimized out>, throwflag=<optimized out>)
    at ../Python/ceval.c:2666
#10 0x00000000004b6cf7 in fast_function (nk=<optimized out>, 
    na=<optimized out>, n=<optimized out>, pp_stack=0x7fffffffbc20, func=
    <function at remote 0xe8a5f0>) at ../Python/ceval.c:4107
#11 call_function (oparg=<optimized out>, pp_stack=0x7fffffffbc20)
    at ../Python/ceval.c:4042
#12 PyEval_EvalFrameEx (f=<optimized out>, throwflag=<optimized out>)
    at ../Python/ceval.c:2666
#13 0x00000000004bcced in PyEval_EvalCodeEx (co=0x7ffff7e1aeb0, 
    globals=<optimized out>, locals=<optimized out>, args=<optimized out>, 
    argcount=<optimized out>, kws=<optimized out>, kwcount=0, defs=
    0x7ffff7e477a8, defcount=1, closure=0x0) at ../Python/ceval.c:3253
#14 0x0000000000449098 in function_call (func=<optimized out>, arg=
    (<TestPkgInfoPackagekit(_testMethodName='test_addons', pkginfo=<PackagekitInfo(_cache={}, _notfound_cache=[], client=<Client at remote 0x51b1be0>, distro=<Ubuntu at remote 0xd1c4d0>) at remote 0x51b1b40>, _cleanups=[], _type_equality_funcs={<type at remote 0x844a00>: 'assertListEqual', <type at remote 0x84e000>: 'assertTupleEqual', <type at remote 0x846c60>: 'assertDictEqual', <type at remote 0x8492c0>: 'assertSetEqual', <type at remote 0x849120>: 'assertSetEqual', <type at remote 0x850fe0>: 'assertMultiLineEqual'}, _resultForDoCleanups=<TextTestResult(_original_stdout=<file at remote 0x7ffff7f9a1e0>, dots=True, skipped=[], _mirrorOutput=False, stream=<_WritelnDecorator(stream=<file at remote 0x7ffff7f9a270>) at remote 0xe8f050>, testsRun=7, buffer=None, _original_stderr=<file at remote 0x7ffff7f9a270>, showAll=False, _stdout_buffer=None, _stderr_buffer=None, _moduleSetUpFailed=False, expectedFailures=[], errors=[], descriptions=True, _previousTestClass=<type at remote 0xec9430>, unexpectedSuccesses=[], failu...(truncated), kw={}) at ../Objects/funcobject.c:526

Do I need a more up-to-date glib or anything like this?