gistfile1.pyw

t =  ( "F",
	 ( "B",
	  ( "A" ),
	  ( "D",
	   ( "C",
	    ( "Z" ),
	    ( "M" )
	   ),
	   ( "E" )
	  )
	 ),  
	 ( "G",
	  (),
	  ( "I",
	   ( "H" ),
	   ()
	  )
	 )
	)

gistfile2.pyw

def Traverse( t, o ):
	if isinstance( o, basestring ):
		order = {
			'pre': [ 0, 1, 2 ],
			'in': [ 1, 0, 2 ],
			'post': [ 1, 2, 0 ],
		}[o]
	else:
		order = o
	
	nodes = []
	for  i in order:
		if isinstance( t[ i ], str ):
			nodes.append( t[ i ] )
		elif len( t[ i ] ) > 1:
			nodes.extend( Traverse( t[ i ], order ))
	return nodes