to ( the with statement and class decorators)or back-ported later to ( set and dictionary comprehensions)but are not available in earlier releases see later sections for more fine-grained information about changes in earlier versionsand see python' "what' newdocuments for changes that may appear in future releases differences the following summarizes tools that differ across python lines unicode string modelin xnormal str strings support all unicode text including asciiand the separate bytes type represents raw -bit byte sequences in xnormal str strings support both -bit text including asciiand separate uni code type represents richer unicode text as an option file modelin xfiles created by open are specialized by content--text files implement unicode encodings and represent content as str stringsand binary files represent content as bytes strings in xfiles use distinct interfaces--files created by open represent content as str strings for content that is either -bit text or bytesbased dataand codecs open implements unicode text encodings class modelin xall classes derive from object automatically and acquire the numerous changes and extensions of new-style classesincluding their differing inheritance algorithmbuilt-ins dispatchand mro search order for diamondpattern trees in xnormal classes follow the classic modeland explicit inheritance from object or other built-in types enables the new-style model as an option built-in iterablesin xmapziprangefilterand dictionary keysvaluesand items are all iterable objects that generate values on request in xthese calls create physical lists printing provides built-in function with keyword arguments for configurationwhile provides statement with special syntax for configuration relative importsboth and support from relative import statementsbut changes the search rule to skip package' own directory for normal imports true divisionboth and support the /floor division operatorbut the is true division in and retains fractional remainderswhile is type-specific in integer types has single integer type that supports extended precision has both normal int and extended longand automatic conversion to long comprehension scopesin xall comprehension forms--listsetdictionarygenerator--localize variables to the expression in xlist comprehensions do not pydocan all-browser pydoc - interface is supported as of and required as of in xthe original pydoc - gui client interface may be used instead byte code storageas of stores byte code files in __pycache__ subdirectory of the source directorywith version-identifying names in xbyte code is stored in the source file directory with generic names appendix cpython changes and this book