python: Add Gst.Float wrapper

When the float python type is used inside a GstValueArray, it is
converted to a G_TYPE_DOUBLE GValue. Sometimes it is important to be
able to force G_TYPE_FLOAT GValue, for instance to set the the
"mix-matrix" property on audioconvert.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8957>

subprojects/gst-python/gi/overrides/Gst.py

@@ -48,6 +48,17 @@ python module to use with Gst 0.10"
     warnings.warn(warn_msg, RuntimeWarning)
 
 
+class Float(float):
+    '''
+    A wrapper to force conversion to G_TYPE_FLOAT instead of G_TYPE_DOUBLE when
+    used in e.g. Gst.ValueArray.
+    '''
+    __gtype__ = GObject.TYPE_FLOAT
+
+
+__all__.append('Float')
+
+
 # Ensuring that PyGObject loads the URIHandler interface
 # so we can force our own implementation soon enough (in gstmodule.c)
 class URIHandler(Gst.URIHandler):

subprojects/gst-python/testsuite/test_types.py

@@ -436,3 +436,26 @@ class TestBitmask(TestCase):
             self.assertEqual(str(r), '0x20')
         else:
             self.assertEqual(str(r), '0x20L')
+
+
+class TestFloat(TestCase):
+    def testSetProperty(self):
+        ''' Test we can set the mix-matrix property on audioconvert
+
+        It requires the Gst.Float class to force the conversion of python float
+        to G_TYPE_FLOAT instead of G_TYPE_DOUBLE.
+        '''
+        Gst.init(None)
+
+        audioconvert = Gst.ElementFactory.make("audioconvert")
+        if not audioconvert:
+            self.skipTest("audioconvert not available")
+
+        row = Gst.ValueArray([Gst.Float(0.0)])
+        matrix = Gst.ValueArray([row])
+        audioconvert.set_property("mix-matrix", matrix)
+
+        value = audioconvert.get_property("mix-matrix")
+        self.assertEqual(len(value), 1)
+        self.assertEqual(len(value[0]), 1)
+        self.assertEqual(value[0][0], 0.0)