How to use the deltachat.capi.ffi.cast function in deltachat

evt_name = get_dc_event_name(evt)
    event_sig_types = capi.lib.dc_get_event_signature_types(evt)
    if data1 and event_sig_types & 1:
        data1 = ffi.string(ffi.cast('char*', data1)).decode("utf8")
    if data2 and event_sig_types & 2:
        try:
            data2 = ffi.string(ffi.cast('char*', data2)).decode("utf8")
        except UnicodeDecodeError:
            # XXX ignoring this error is not quite correct but for now
            # i don't want to hunt down encoding problems in the c lib
            data2 = ffi.string(ffi.cast('char*', data2))

    try:
        ret = callback(ctx, evt_name, data1, data2)
        if event_sig_types & 4:
            return ffi.cast('uintptr_t', ret)
        elif event_sig_types & 8:
            return ffi.cast('int', ret)
    except:  # noqa
        raise
        ret = 0
    return ret

if data1 and event_sig_types & 1:
        data1 = ffi.string(ffi.cast('char*', data1)).decode("utf8")
    if data2 and event_sig_types & 2:
        try:
            data2 = ffi.string(ffi.cast('char*', data2)).decode("utf8")
        except UnicodeDecodeError:
            # XXX ignoring this error is not quite correct but for now
            # i don't want to hunt down encoding problems in the c lib
            data2 = ffi.string(ffi.cast('char*', data2))

    try:
        ret = callback(ctx, evt_name, data1, data2)
        if event_sig_types & 4:
            return ffi.cast('uintptr_t', ret)
        elif event_sig_types & 8:
            return ffi.cast('int', ret)
    except:  # noqa
        raise
        ret = 0
    return ret