advent_13.py

def key(x, y):
  return "{0}-{1}".format(x, y)

def fold(points, axis, fold_point):
  fold_changes = []
  for point_key in points:
    x, y = points[point_key]
    if axis == 'y':
      if y > fold_point:
        fold_changes.append((x, y, x, fold_point - (y - fold_point)))
    else:
      if x > fold_point:
        fold_changes.append((x, y, fold_point - (x - fold_point), y))
  for old_x, old_y, new_x, new_y in fold_changes:
    points.pop(key(old_x, old_y), None)
    points[key(new_x, new_y)] = (new_x, new_y)

def pretty_print(points):
  point_list = sorted(points.values(), key = lambda item: (item[1], item[0]))
  last_y = -1
  idx = 0
  line = ''
  last_x = 0
  while idx < len(point_list):
    x, y = point_list[idx]
    if y > last_y:
      # New line
      last_x = 0
      print(line)
      line = ''
    line += ' ' * (x - last_x - 1)
    line += '#'
    last_x = x
    last_y = y
    idx += 1
  print(line)

if __name__ == '__main__':
  with open('input.txt') as data:
    points = {}
    reading_folds = False
    for line in data:
      line = line.strip()
      if not line:
        reading_folds = True
        continue
      if not reading_folds:
        x, y = line.split(',')
        points[key(x, y)] = (int(x), int(y))
      else:
        axis, value = line.split(' ')[2].split('=')
        fold(points, axis, int(value))
        print(len(points))
    pretty_print(points)