Secure empty lines before and after completed snippets with UltiSnips

python.snippets

global !p
def on_jump(snippet, positions, function, arguments=None):
	if not isinstance(positions, list):
		positions = [positions]

	for position in positions:
		if position == "last":
			position = len(snippet.tabstops) - 1

		if position == snippet.tabstop:
			if arguments:
				function(arguments)
			else:
				function()

def secure_empty_line_wrap(arguments):
	snippet, count_before, count_after = arguments[0:3]
	force_count = arguments[3] if len(arguments) > 3 else False

	last_line = len(snippet.buffer) - 1

	snippet_start = snippet.snippet_start[0]
	snippet_end   = snippet.snippet_end[0] + 1

	index_before = snippet_start - count_before
	index_after = snippet_end + count_after

	if snippet_start > 0:
		for index in reversed(range(index_before, snippet_start)):
			if snippet.buffer[index]:
				missing_empty_lines = index - index_before + 1
				snippet.buffer.append([''] * missing_empty_lines, index + 1)
				snippet_end += missing_empty_lines
				index_after += missing_empty_lines
				last_line += missing_empty_lines
				added_lines_before = missing_empty_lines
				break

			elif index == index_before and force_count:
				while True:
					index -= 1
					if snippet.buffer[index]: break
					del snippet.buffer[index]
					snippet_end -= 1
					index_after -= 1
					last_line -= 1

	if snippet_end < last_line:
		for index in range(snippet_end, index_after):
			if snippet.buffer[index]:
				missing_empty_lines = index_after - index
				snippet.buffer.append([''] * missing_empty_lines, index)
				break

			elif index == index_after - 1 and force_count:
				index += 1

				while True:
					if snippet.buffer[index]: break
					del snippet.buffer[index]

endglobal


# Primitive snippets to show usability.

pre_expand "snip.buffer[snip.line] = ''; snip.cursor.set(snip.line, 0)"
post_jump "on_jump(snip, 'last', secure_empty_line_wrap, [snip, 2, 1, True])"
snippet class "class" bmA
class ${1:ClassName}($2):
  ${3:${VISUAL}}
endsnippet

post_jump "on_jump(snip, 'last', secure_empty_line_wrap, [snip, 1, 1])"
snippet def "function" bma
  def ${1:function_name}($2):
    ${3:${VISUAL:pass}}
endsnippet