Hi meddahi,
as written in the documentation (https://knowage-suite.readthedocs.io/en/7.2/functionalities-guide/cockpit/index.html#custom-chart-widget) you have to enable first the widget for the specified role.Being the functionality really advanced you have to explicitally declare which user will be able to manage it in the role management section.
Remember to logout after saving the new role settings to make the changes effective for your role.Regards.
Davide
For specific informations on python widget installation please follow the instructions here:https://knowage-suite.readthedocs.io/en/7.2/installation-guide/python-installation.html