class_docstr: Computes the arc length of a streamline. 
class_docstr_tok: ["Computes","the","arc","length","of","a","streamline","."]
docstr: Infers the shape of features extracted from `streamline`. 
docstr_tok: ["Infers","the","shape","of","features","extracted","from","`","streamline","`","."]
code: def infer_shape(self, streamline):
      """Infers the shape of features extracted from `streamline`."""
      # Arc length is a scalar
      return 1
  
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 2 for calling the ArcLengthFeature obj's underlying member method code with example usage: obj.infer_shape(streamline) and returns: int