code: def __find_executables(path):
      
  
      success = False
      progs = {
          "dot": "",
          "twopi": "",
          "neato": "",
          "circo": "",
          "fdp": "",
          "sfdp": "",
      }
  
      was_quoted = False
      path = path.strip()
      if path.startswith('"') and path.endswith('"'):
          path = path[1:-1]
          was_quoted = True
  
      if not os.path.isdir(path):
          return None
  
      for prg in progs:
          if progs[prg]:
              continue
  
          prg_path = os.path.join(path, prg)
          prg_exe_path = prg_path + ".exe"
  
          if os.path.exists(prg_path):
              if was_quoted:
                  prg_path = "\"{}\"".format(prg_path)
              progs[prg] = prg_path
              success = True
  
          elif os.path.exists(prg_exe_path):
              if was_quoted:
                  prg_exe_path = "\"{}\"".format(prg_exe_path)
              progs[prg] = prg_exe_path
              success = True
  
      if success:
          return progs
  
      return None
docs: Used by find_graphviz
  
      path - single directory as a string
  
      If any of the executables are found, it will return a dictionary
      containing the program names as keys and their paths as values.
  
      Otherwise returns None