python: Add a Gst.init_python function to be called from plugins

Plugins know that they will be initialized after Gst was initialized
so they can call the initialization function dedicated for the python
bindings

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2737>

subprojects/gst-python/examples/plugins/python/audioplot.py

@@ -29,7 +29,7 @@ except ImportError:
     raise
 
 
-Gst.init(None)
+Gst.init_python()
 
 AUDIO_FORMATS = [f.strip() for f in
                  GstAudio.AUDIO_FORMATS_ALL.strip('{ }').split(',')]

subprojects/gst-python/examples/plugins/python/exampleTransform.py

@@ -15,7 +15,7 @@ from gi.repository import Gst, GObject, GstBase, GstVideo
 
 import numpy as np
 
-Gst.init(None)
+Gst.init_python()
 FIXED_CAPS = Gst.Caps.from_string('video/x-raw,format=GRAY8,width=[1,2147483647],height=[1,2147483647]')
 
 class ExampleTransform(GstBase.BaseTransform):

subprojects/gst-python/examples/plugins/python/identity.py

@@ -16,7 +16,7 @@ import gi
 gi.require_version('GstBase', '1.0')
 
 from gi.repository import Gst, GObject, GstBase
-Gst.init(None)
+Gst.init_python()
 
 #
 # Simple Identity element created entirely in python

subprojects/gst-python/examples/plugins/python/mixer.py

@@ -20,7 +20,7 @@ gi.require_version('GObject', '2.0')
 
 from gi.repository import Gst, GObject, GstBase
 
-Gst.init(None)
+Gst.init_python()
 
 try:
     from PIL import Image

subprojects/gst-python/examples/plugins/python/py_audiotestsrc.py

@@ -22,6 +22,8 @@ except ImportError:
     Gst.error('py_audiotestsrc requires numpy')
     raise
 
+Gst.init_python()
+
 OCAPS = Gst.Caps.from_string (
         'audio/x-raw, format=F32LE, layout=interleaved, rate=44100, channels=2')
 

subprojects/gst-python/examples/plugins/python/sinkelement.py

@@ -17,7 +17,7 @@
 #  $ GST_DEBUG=python:4 gst-launch-1.0 fakesrc num-buffers=10 ! mysink
 
 from gi.repository import Gst, GObject, GstBase
-Gst.init(None)
+Gst.init_python()
 
 #
 # Simple Sink element created entirely in python

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

@@ -747,7 +747,14 @@ def deinit():
     deinit_pygst()
     return real_deinit()
 
+def init_python():
+    if not Gst.is_initialized():
+        raise NotInitialized("Gst.init_python should never be called before GStreamer itself is initialized")
+
+    init_pygst()
+
 Gst.deinit = deinit
+Gst.init_python = init_python
 
 if not Gst.is_initialized():
     deinit_pygst()