Namespace Gst not available (newbie)

[tasos]

Hello and i'm sorry for the entry level question.
I'm using Slackware 15 and i have installed gstreamer from source code.
I'm trying to run a simple program


> #!/usr/bin/env python3
> import gi
> gi.require_version('Gst', '1.0')
> gi.require_version('Gtk', '3.0')
> from gi.repository import Gst, GObject, Gtk

and i get

> ValueError: Namespace Gst not available

meson configure:

> Executing subproject gst-python 
> 
> gst-python| Project name: gst-python
> gst-python| Project version: 1.21.2.1
> gst-python| C compiler for the host machine: ccache cc (gcc 11.2.0 "cc (GCC) 11.2.0")
> gst-python| C linker for the host machine: cc ld.bfd 2.37-slack15
> gst-python| Dependency gstreamer-1.0 found: YES 1.21.2.1 (overridden)
> gst-python| Dependency gstreamer-base-1.0 found: YES 1.21.2.1 (overridden)
> gst-python| Dependency gmodule-no-export-2.0 found: YES 2.70.3 (cached)
> gst-python| Dependency pygobject-3.0 found: YES 3.42.0 (cached)
> gst-python| Program python3 found: YES (/usr/bin/python3)
> gst-python| Message: pylib_loc = /usr/lib64
> gst-python| Message: python_abi_flags =
> gst-python| Message: pylib_loc = /usr/lib64
> gst-python| Message: pygobject overrides directory = /usr/local/lib64/python3.9/site-packages/gi/overrides
> gst-python| Configuring config.h using configuration
> gst-python| Build targets in project: 1546
> gst-python| Subproject gst-python finished.
> 
> meson.build:178: WARNING: DEPRECATED use of the `plugins` variable in gst-python.
> meson.build:179: WARNING: The variable should now be called `gst_plugins` and use:
> meson.build:180: WARNING: `declare_dependency( link_with: <plugin_target>, variable: {'full_path': <plugin_target>.full_path()})` instead

After searching for a solution i think the problem has to do with

> Message: pygobject overrides directory 

So gstreamer installs

>  /usr/local/lib64/python3.9/site-packages/gi/overrides/

and the override happens here

> /usr/local/lib64/python3.9/site-packages/gi/overrides

I tried to copy the files from /usr/local to the former directory but with no luck.

Any ideas?
Thanks in advance!