Print out a nested list as a tree with line-drawing characters

unicode-tree.py

#! python3

def first_then(first, then):
	yield first
	while True:
		yield then

prefix_one = lambda: first_then('━━', '  ')
prefix_many_first = lambda: first_then('┳━', '┃ ')
prefix_many_rest = lambda: first_then('┣━', '┃ ')
prefix_many_last = lambda: first_then('┗━', '  ')


def tree_lines(x):
	if type(x) is tuple:
		if len(x) == 1:
			# singular tuple
			for p, l in zip(prefix_one(), tree_lines(x[0])):
				yield p + l
		else:
			first, rest, last = x[0], x[1:-1], x[-1]

			# first entry
			for p, l in zip(prefix_many_first(), tree_lines(first)):
				yield p + l

			# middle entries
			for y in rest:
				for p, l in zip(prefix_many_rest(), tree_lines(y)):
					yield p + l

            # last entries
			for p, l in zip(prefix_many_last(), tree_lines(last)):
				yield p + l
	else:
		yield str(x)

if __name__ == '__main__':
  x = ((('A','B'),('C','D')),'E')

  for l in tree_lines(x):
    print(l)