loading.py

class QSelfLoadingWidgetMixin:
    """Load UI and CSS files into current instance

    Expects a dict containing "ui" mandatory and "css" optional keys.
    """
    def __init__(self, resource_files=None, parent=None):
        super().__init__(parent)
        if resource_files:
            ui_file = resource_files.get("ui")
            css_file = resource_files.get("css")
        else:
            ui_file, css_file = None, None
        if ui_file:
            loadUi(ui_file, self)
            if css_file:
                with open(css_file) as css_file:
                    self.setStyleSheet(css_file.read())