code: def filter_above_threshold(
              self,
              key_fn,
              value_dict,
              threshold,
              default_value=0.0):
          
          def filter_fn(x):
              key = key_fn(x)
              value = value_dict.get(key, default_value)
              return value > threshold
          return self.filter(filter_fn)
docs: The code for filtering by gene or transcript expression was pretty
          much identical aside from which identifier you pull off an effect.
          So, factored out the common operations for filtering an effect
          collection into this helper method.
  
          Parameters
          ----------
          key_fn : callable
              Given an element of this collection, returns a key into `value_dict`
  
          value_dict : dict
              Dict from keys returned by `extract_key_fn` to float values
  
          threshold : float
              Only keep elements whose value in `value_dict` is above this
              threshold.
  
          default_value : float
              Value to use for elements whose key is not in `value_dict`