code: def inasafe_analysis_summary_field_value(field, feature, parent):
      
      _ = feature, parent  # NOQA
      project_context_scope = QgsExpressionContextUtils.projectScope(
          QgsProject.instance())
      registry = QgsProject.instance()
  
      key = provenance_layer_analysis_impacted_id['provenance_key']
      if not project_context_scope.hasVariable(key):
          return None
  
      layer = registry.mapLayer(project_context_scope.variable(key))
  
      if not layer:
          return None
  
      index = layer.fields().lookupField(field)
      if index < 0:
          return None
  
      feature = next(layer.getFeatures())
      return feature[index]
docs: Retrieve a value from a field in the analysis summary layer.
  
      e.g. inasafe_analysis_summary_field_value('total_not_exposed') -> 3