Python 3.7

dict objects must preserve insertion-order

More than 255 arguments can now be passed to a function; a function can now have more than 255 parameters

bytes.fromhex() and bytearray.fromhex() now ignore all ASCII whitespace, not only spaces

str, bytes, and bytearray gained support for the new isascii() method, which can be used to test if a string or bytes contain only the ASCII characters

ImportError now displays module name and module __file__ path when from ... import ... fails

Circular imports involving absolute imports with binding a submodule to a name are now supported

object.__format__(x, '') is now equivalent to str(x) rather than format(str(self), '')

In order to better support dynamic creation of stack traces, types.TracebackType can now be instantiated from Python code, and the tb_next attribute on tracebacks is now writable

When using the -m switch, sys.path[0] is now eagerly expanded to the full starting directory path, rather than being left as the empty directory (which allows imports from the current working directory at the time when an import occurs)

The new -X importtime option or the PYTHONPROFILEIMPORTTIME environment variable can be used to show the timing of each module import