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 index where *edge* appears in the current front.
  
  If the edge is not in the front, return -1
docstr_tok: ["Return","the","index","where","*","edge","*","appears","in","the","current","front",".","If","the","edge","is","not","in","the","front",",","return","-1"]
code: def _edge_in_front(self, edge):
      """Return the index where *edge* appears in the current front.
  
      If the edge is not in the front, return -1
      """
      e = (list(edge), list(edge)[::-1])
      for i in range(len(self._front) - 1):
          if self._front[i : i + 2] in e:
              return i
      return -1
  
imports: from __future__ import division, print_function
  from itertools import permutations
  import numpy
  from collections import OrderedDict
label_desc: Use image node_id 8 for calling the Triangulation obj's underlying member method code with example usage: obj._edge_in_front(edge) and returns: unknown, i