class_docstr: Constrained delaunay triangulation
  
  Implementation based on [1]_.
  
  Parameters
  ----------
  pts : array
      Nx2 array of points.
  edges : array
      Nx2 array of edges (dtype=int).
  
  Notes
  -----
  * Delaunay legalization is not yet implemented. This produces a proper
    triangulation, but adding legalisation would produce fewer thin
    triangles.
  * The pts and edges arrays may be modified.
  
  References
  ----------
  .. [1] Domiter, V. and Žalik, B. Sweep‐line algorithm for constrained
     Delaunay triangulation
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docstr: Return the only tri that contains *edge*.
  
  If two tris share this edge, raise an exception.
docstr_tok: ["Return","the","only","tri","that","contains","*","edge","*",".","If","two","tris","share","this","edge",",","raise","an","exception","."]
code: def _tri_from_edge(self, edge):
      """Return the only tri that contains *edge*.
  
      If two tris share this edge, raise an exception.
      """
      edge = tuple(edge)
      p1 = self._edges_lookup.get(edge, None)
      p2 = self._edges_lookup.get(edge[::-1], None)
      if p1 is None:
          if p2 is None:
              raise RuntimeError(
                  "No tris connected to edge %r" % (edge,)
              )
          return edge + (p2,)
      elif p2 is None:
          return edge + (p1,)
      else:
          raise RuntimeError(
              "Two triangles connected to edge %r" % (edge,)
          )
  
imports: from __future__ import division, print_function
  from itertools import permutations
  import numpy
  from collections import OrderedDict
label_desc: Use image node_id 11 for calling the Triangulation obj's underlying member method code with example usage: obj._tri_from_edge(edge) and returns: unknown, unknown