docs: def pep8_lines_between_cells(prev_lines, next_lines, ext):
      """How many blank lines should be added between the two python paragraphs to make them pep8?"""
      if not next_lines:
          return 1
      if not prev_lines:
          return 0
      if ext != '.py':
          return 1
      if cell_ends_with_function_or_class(prev_lines):
          return 2 if cell_has_code(next_lines) else 1
      if cell_ends_with_code(prev_lines) and next_instruction_is_function_or_class(next_lines):
          return 2
      return 1