class_docstr: Computes the arc length of a streamline. 
class_docstr_tok: ["Computes","the","arc","length","of","a","streamline","."]
code: def __init__(self):
      # The arc length stays the same even if the streamline is reversed.
      super(ArcLengthFeature, self).__init__(is_order_invariant=True)
  
file_path: dipy/doc/examples/segment_extending_clustering_framework.py
imports: import numpy
  from dipy.data import get_fnames
  from dipy.io.streamline import load_tractogram
  from dipy.tracking.streamline import Streamlines
  from dipy.viz import window, actor, colormap
  from dipy.segment.clustering import QuickBundles
  from dipy.segment.featurespeed import Feature, VectorOfEndpointsFeature
  from dipy.segment.metric import Metric, SumPointwiseEuclideanMetric
  from dipy.tracking.streamline import length
label_desc: Use image node_id 1 to create a new ArcLengthFeature object from inherited base classes: Feature with example: obj = ArcLengthFeature()