Here is a patch that restores compatibility. There were no tests for print_stack(), format_stack(), and extract_stack() without arguments. New tests are passed with 3.4.

There is a difference between this bug and warnings.warn(stacklevel=) at import time. In the latter the behavior is changed when we specify the stacklevel and we can't workaround this besides change the specified stacklevel depending on Python version. In the former the behavior is changed only when we don't specify a frame. The workaround is version independed: specify the frame explicitly. Therefore we will not break a code with a workaround for 3.5.0, but will fix a code without workaround.