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ASCII Display of Trees

From: andrew cooke <andrew@...>

Date: Mon, 30 May 2011 21:50:58 -0400

Here's an example in Python that I hope is simple enough to be used in other
languages too:


  #!/usr/bin/python

  class Tree(object):

      def __init__(self, name, *children):
	  self.name = name
	  self.children = children

      def __str__(self):
	  return '\n'.join(self.tree_lines())

      def tree_lines(self):
	  yield self.name
	  last = self.children[-1] if self.children else None
	  for child in self.children:
	      prefix = '`-' if child is last else '+-'
	      for line in child.tree_lines():
		  yield prefix + line
		  prefix = '  ' if child is last else '| '

      # an alternative without generators
      def tree_lines_2(self):
	  lines = []
	  lines.append(self.name)
	  last = self.children[-1] if self.children else None
	  for child in self.children:
	      prefix = '`-' if child is last else '+-'
	      for line in child.tree_lines():
		  lines.append(prefix + line)
		  prefix = '  ' if child is last else '| '
	  return lines


  tree = Tree('a',
	   Tree('b',
	     Tree('c'),
	     Tree('d',
	       Tree('e')),
	     Tree('f',
	       Tree('g'),
	       Tree('h'))),
	   Tree('i'))

  # this calls __str__() and tree_lines()
  print tree

  # an alternative, avoiding Python-specific idioms
  for line in tree.tree_lines_2():
      print line


The output is (twice):

  > ./tree.py
  a
  +-b
  | +-c
  | +-d
  | | `-e
  | `-f
  |   +-g
  |   `-h
  `-i


Also foo[-1] is the last element of array foo.

Andrew

PS This code in public domain.

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