code: def evaluate(self, environment=None):
          
          current_environment = default_environment()
          if environment is not None:
              current_environment.update(environment)
  
          return _evaluate_markers(self._markers, current_environment)
docs: Evaluate a marker.
  
          Return the boolean from evaluating the given marker against the
          environment. environment is an optional argument to override all or
          part of the determined environment.
  
          The environment is determined from the current Python process.