because it bears heavily on this book' contenti need to say few more words about the python / story up front when the fourth edition of this book was written in python had just become available in two flavorsversion was the first in the line of an emerging and incompatible mutation of the language known generically as version retained backward compatibility with the vast body of existing python codeand was the latest in the line known collectively as while was largely the same languageit ran almost no code written for prior releases itimposed unicode model with broad consequences for stringsfilesand libraries elevated iterators and generators to more pervasive roleas part of fuller functional paradigm mandated new-style classeswhich merge with typesbut grow more powerful and complex changed many fundamental tools and librariesand replaced or removed others entirely the mutation of print from statement to function aloneaesthetically sound as it may bebroke nearly every python program ever written and strategic potential aside ' mandatory unicode and class models and ubiquitous generators made for different programming experience although many viewed python as both an improvement and the future of pythonpython was still very widely used and was to be supported in parallel with python for years to come the majority of python code in use was xand migration to seemed to be shaping up to be slow process the / story today as this fifth edition is being written in python has moved on to versions and but this / story is still largely unchanged in factpython is now dual-version worldwith many users running both and according to their software goals and dependencies and for many newcomersthe choice between and remains one of existing software versus the language' cutting edge although many major python packages have been ported to xmany others are still -only today to some observerspython is now seen as sandbox for exploring new ideaswhile is viewed as the tried-and-true pythonwhich doesn' have all of ' features but is still more pervasive others still see python as the futurea view that seems supported by current core developer planspython will continue to be supported but is to be the last xwhile is the latest in the line' continuing evolution xxxvi preface