Help with Gst.Iterator.find_custom() in python

[Mathieu Duponchelle]

eg:

def gst_bin_get_by_gtype(b, type_name):

    factory = Gst.ElementFactory.find(type_name)

    return None if factory is None else next(filter(lambda c: c.__gtype__ == factory.get_element_type(), b.iterate_recurse()), None)


On 5/21/21 5:51 PM, Mathieu Duponchelle via gstreamer-devel wrote:
> Looks like a bug in pygobject, I tried to pinpoint it but that code base is
> a bit of a maze :(
>
> And I think there's actually two bugs: one is the parameters passed back
> to the closure as you noticed, the other one is the final return value when
> no match was found, these are two separate issues.
>
> Note that the gst-python overrides let you iterate the GstIterator as a normal
> python iterator, why don't you simply loop over it to find your object?
>
>> Hi, I'm trying to create a function in python to find elements in a bin based
>> on their type (not name).
>
> On 5/21/21 9:24 AM, Marianna S. Buschle via gstreamer-devel wrote:
>> Hi, I'm trying to create a function in python to find elements in a bin based
>> on their type (not name).
>>
>> I have such a function in C which works and I'm trying to convert it to
>> python but I'm experiencing some issues.
>>
>> def compare_gtype(element, type):
>>     print(element)
>>     print(type)
>>     
>>     return 1
>>
>> def gst_bin_get_by_gtype(bin, type_name):
>>     factory = Gst.ElementFactory.find(type_name)
>>     type = factory.get_element_type()
>>     print(type_name)
>>     print(type)
>>     
>>     print("[" + bin.get_name() + "]: looking up child element of type " +
>> type.name)
>>
>>     children = bin.iterate_recurse()        
>>     if children:
>>         print(children)
>>         print(children.type)
>>         found, elem = children.find_custom(compare_gtype, type)
>>     else:
>>         print("Error")
>>
>>     if found:
>>         print("Found")
>>         return elem
>>     else:
>>         print("Not Found")
>>         return None
>>
>> This is the output I get:
>>
>> filesink
>> <GType GstFileSink (140449056935968)>
>> [pipeline0]: looking up child element of type GstFileSink
>> <Gst.Iterator object at 0x7fbcded2bdc0 (GstIterator at 0x7fbcd0009220)>
>> <GType GstElement (140449054520272)>
>> <GType GstFileSink (140449056935968)>
>> 140448920294640
>> <GType GstFileSink (140449056935968)>
>> 140448920294640
>> <GType GstFileSink (140449056935968)>
>> 140448920294640
>> <GType GstFileSink (140449056935968)>
>> 140448920294640
>> <GType GstFileSink (140449056935968)>
>> 140448920294640
>> API Exception: {'type': 'TypeError', 'args': ('unknown type (null)',),
>> 'message': 'unknown type (null)'}
>> Traceback (most recent call last):
>>   File "/usr/lib/python3/dist-packages/jsonrpc/manager.py", line 113, in
>> _get_responses
>>     result = method(*request.args, **request.kwargs)
>>   File "/home/msb/QtecGit/python-tests/gst_ctrl.py", line 248, in play
>>     gst_handler.play(index)
>>   File "/home/msb/QtecGit/python-tests/gst_ctrl.py", line 69, in play
>>     elem = gst_bin_get_by_gtype(self.pipeline[index], "filesink")
>>   File "/home/msb/QtecGit/python-tests/gst_ctrl.py", line 42, in
>> gst_bin_get_by_gtype
>>     found, elem = children.find_custom(compare_gtype, type)
>> TypeError: unknown type (null)
>>
>> So for me it seems like the find_custom() is not passing the GstElement from
>> the iterator to the compare_gtype() function...
>>
>> And this is the pipeline it is searching (no filesink):
>> filesrc name=replay location=/home/msb/test.ts ! decodebin ! videoconvert !
>> ximagesink sync=1
>>
>> And just for reference the code in C:
>>
>> static gint
>> compare_gtype(const GValue *velement, GType type)
>> {
>> 	gint eq = 1;
>> 	GstElement *element = g_value_get_object(velement);
>>
>> 	GST_OBJECT_LOCK(element);
>> 	if (G_OBJECT_TYPE(element) == type)
>> 		eq = 0;
>> 	GST_OBJECT_UNLOCK(element);
>>
>> 	return eq;
>> }
>>
>> static GstElement *
>> gst_bin_get_by_gtype(GstBin *bin, GType type)
>> {
>> 	GstIterator *children;
>> 	GValue result = { 0, };
>> 	GstElement *element;
>> 	gboolean found;
>>
>> 	g_return_val_if_fail(GST_IS_BIN(bin), NULL);
>>
>> 	QTEC_DEBUG("[%s]: looking up child element of type %s",
>> 		   GST_ELEMENT_NAME(bin), g_type_name(type));
>>
>> 	children = gst_bin_iterate_recurse(bin);
>> 	found = gst_iterator_find_custom(children,
>> 					 (GCompareFunc) compare_gtype,
>> 					 &result, (gpointer) type);
>> 	gst_iterator_free(children);
>>
>> 	if (found) {
>> 		element = g_value_dup_object(&result);
>> 		g_value_unset(&result);
>> 	} else {
>> 		element = NULL;
>> 	}
>>
>> 	return element;
>> }
>>
>>         GstElementFactory * proxysrc_factory =
>> gst_element_factory_find("proxysrc");
>>
>> 	if (!proxysrc_factory)
>> 		return FALSE;
>>
>> 	GType proxysrc_type =
>> gst_element_factory_get_element_type(proxysrc_factory);
>>
>> 	GstElement *psrc = gst_bin_get_by_gtype(GST_BIN(bin), proxysrc_type);
>>
>>
>>
>> --
>> Sent from: http://gstreamer-devel.966125.n4.nabble.com/
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