integers and integer division python no longer has an int type for -bit integers and separate long type for long integers the int type now represents an integer of arbitrary precision (the internal details of which are not exposed to the userin additioninteger division now always produces floating-point result for example / is not the conversion to float applies even if the result would have been an integer for example / is not comparisons python is much more strict about how values are compared in python it is the case that any two objects can be compared even if it doesn' make sense for example "hellotrue in python this results in typeerror for example "hellotraceback (most recent call last)file ""line in typeerrorunorderable typesint(str(this change is minorbut it means that in python you have to be much more careful about making sure data is of appropriate types for exampleif you use the sort(method of listall of the items in the list must be compatible with the operatoror you get an error in python the operation would be silently carried out anyways with usually meaningless result iterators and generators python has made slight change to the iterator protocol instead of calling _iter_ (and the next(method to perform iterationthe next(method has been renamed to _next_ (most users will be unaffected by this change except if you have written code that manually iterates over an iterable or if you have defined your own custom iterator objects you will need to make sure you change the name of the next(method in your classes use the built-in next(function to invoke the next(or _next_ (method of an iterator in portable manner file namesargumentsand environment variables in python filenamescommand-line arguments in sys argvand environment variables in os environ may or may not be treated as unicode depending on local settings the only problem is that the usage of unicode within the operating system environment is not entirely universal for exampleon many systems it may be technically possible to specify filenamescommand-line optionsand environment variables that are just raw sequence of bytes that don' correspond to valid unicode encoding although these situations might be rare in practiceit may be of some concern for programming using python to perform tasks related to systems administration as previously notedsupplying file and directory names as byte strings will fix many of the problems for exampleos listdir( '/foo' lib fl ff