Sensible changes. http://codereview.appspot.com/815042/diff/1/Lib/doctest.py File Lib/doctest.py (right): http://codereview.appspot.com/815042/diff/1/Lib/doctest.py#newcode363 Lib/doctest.py:363: raise ValueError('Absolute path specified as module-relative' + You missed a space at the end of the line. You can rely on implicit string concatenation instead of using +. http://codereview.appspot.com/815042/diff/1/Lib/doctest.py#newcode364 Lib/doctest.py:364: 'path: ' + path) Is it possible that path is not a string? If so, this error message would blow up.