general apply to instances of user-defined classes in shortin python and for new-style classes in python xthe type of class instance is the class from which the instance was made for classic classes in python xall class instances are instead of the type "instance,and we must compare instance __class__ attributes to compare their types meaningfully since we're not yet equipped to tackle the subject of classeswe'll postpone the rest of this story until other types in python besides the core objects studied in this part of the bookand the program-unit objects such as functionsmodulesand classes that we'll meet latera typical python installation has dozens of additional object types available as linked-in extensions or python classes--regular expression objectsdbm filesgui widgetsnetwork socketsand so on depending on whom you askthe named tuple we met earlier in this may fall in this category too (decimal and fraction of tend to be more ambiguousthe main difference between these extra tools and the built-in types we've seen so far is that the built-ins provide special language creation syntax for their objects ( for an integer[ , for listthe open function for filesand def and lambda for functionsother tools are generally made available in standard library modules that you must first import to useand aren' usually considered core types for instanceto make regular expression objectyou import re and call re compile(see python' library reference for comprehensive guide to all the tools available to python programs built-in type gotchas that' the end of our look at core data types we'll wrap up this part of the book with discussion of common problems that seem to trap new users (and the occasional expert)along with their solutions some of this is review of ideas we've already coveredbut these issues are important enough to warn about again here assignment creates referencesnot copies because this is such central concepti'll mention it againshared references to mutable objects in your program can matter for instancein the following examplethe list object assigned to the name is referenced both from and from inside the list assigned to the name changing in place changes what referencestool [ [' ' ' ' [' '[ ]' 'embed reference to tuplesfilesand everything else