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This page lists features that ''Guido van Rossum himself'' has mentioned as goals for Python 3.0. Parts of this page have been consolidated into PEP 3000 [[[#e|5]]] This page lists features that ''Guido van Rossum himself'' has mentioned as goals for Python 3.0. Parts of this page have been consolidated into PEP 3000 [[#e|[5]]]

This page lists features that Guido van Rossum himself has mentioned as goals for Python 3.0. Parts of this page have been consolidated into PEP 3000 [5]

Status

Python 3.0 is currently (2008-07-12) in beta testing, and has much accumulated documentation. More official sources of information include:

Unfortunately there does not appear to be a well-maintained single point of entry for someone to find all relevant changes that will occur in Python 3.0.

Core Language Changes

  • Remove distinction between int and long types. 4]

  • Make true division the default behavior. 4]

  • Make all strings unicode 4], and have a separate bytes 2] type. 13]

  • Make the exec statement a function again. 1]

  • Remove old-style classes. 4]

  • Replace the print statement with a function or functions. (e.g. write(x, y, z), writeline(x, y, z)) 1] 21]

  • Make as a real keyword. 7]

  • Add an attribute to exceptions for storing the traceback. 22]

  • Remove raise Exception, 'message' syntax in favor of raise Exception('message'). 11] 20]

  • Require that the first statement of a suite be on its own line. 1]

  • Make True and False keywords. 6]

    • Reason: make assignment to them impossible.

  • Raise an exception when making comparisons (other than equality and inequality) between two incongruent types. 24]

    • Reason: such comparisons do not make sense and are especially confusing to new users of Python.

  • Require that all exceptions inherit a common base class. 9]

    • Reason: forces the use of classes as objects raised by exceptions and simplifies the implementation.

  • Make the traceback a standard attribute of Exception instances 18]

    • Reason: inconvenient to pass the (type, value, traceback) triple that currently represents an exception around.

  • Remove `x`. 1]

    • Instead: use repr(x).

    • Reason: backticks are hard to read in many fonts and can be mangled by typesetting software.

  • Remove the <> operator.

    • Instead: use !=.

  • Remove support for string exceptions. 1]

    • Instead: use a class.

  • Add a mechanism so that multiple exceptions can be caught using except E1, E2, E3:. For instance: 

       1 except E1, E2, E3 as err:  # Store error variable
   2    ...
    (Added by GvR, suggested by Bram Cohen.)

    • JimD's suggested syntax: 

         1 except (E1, E2, E3), e:
   2    ...
   3 
   4 except E1, e:
   5    ...

      The except code would then basically do the equivalent of if issubclass(arg1, Exception) or isinstance(arg1, Exception): ... else if len(arg1): ... (excepting, obviously, that this is implemented at a lower level in the C core). --JimD

  • Perhaps have optional declarations for static typing.

    • GvR suggested the syntax 17]: (but NOT for static typing - for declaring type information that would be checked at runtime, not compile time) 

         1 def bar(low: int, high: int) -> float:
   2     ...

    • Since some types only implement parts of an interface have 'strict' and 'lax' interfaces. Strict requires a complete implementation of the interface, lax requiring only a partial implementation with the rest being taken from interface defaults or ignored. This would require a new keyword/reserved word (strict) with lax mode being the default. This is to help duck typing. Ex: 

         1 def baz(x as list, y as strict file):
   2     # x must only (be adapted to) implement part of the list interface
   3     # y must (be adapted to) implement the whole file interface

    • Another proposal: Use -> and => as type conversion operators (lax and strict, respectively). 

         1 def qux(x -> list, y => file):
   2     # x must only (be adapted to) implement part of the list interface
   3     # y must (be adapted to) implement the whole file interface

Built-In Changes

  • Have range(), zip(), dict.keys(), dict.items(), and dict.values() return iterators.

  • Move compile(), intern() and id() to the sys module. 1]

  • Change max() and min() to consume iterators.

  • Remove coerce() as it is obsolete. 1]

  • Introduce trunc(), which would call the __trunc__() method on its argument.

    • Reason: used for objects like floats where calling __int__() has data loss but an integral representation is still desired. 25]

  • Remove dict.iteritems(), dict.iterkeys(), and dict.itervalues().

    • Instead: use dict.items(), dict.keys(), and dict.values() respectively.

  • Remove apply(). 1]

    • Instead: use f(*args, **kw).

  • Remove xrange(). 1] 4]

    • Instead: use range().

  • Remove reduce(). 1]

    • Instead: use functools.reduce().

  • Remove callable(). 1]

    • Instead: use hasattr to check for __call__ attribute.

  • Remove buffer(). 1] 2]

    • Instead: use new bytes type.

  • Remove raw_input(). 1]

    • Instead: use input().

  • Remove input(). 1]

    • Instead: use eval(input()).

  • Remove execfile() and reload(). 1]

    • Instead: use exec().

  • Remove basestring.find() and basestring.rfind(). 23]

    • Instead: use basestring.index() and basestring.rindex() in a try/except block.

Standard Library Changes

  • Remove types module.

    • Instead: use the types in __builtins__.

  • Remove other deprecated modules. 3]

  • Remove sys.exc_type. 1]

    • Instead: use sys.exc_info.

    • Reason: it is not thread safe.
  • Reorganize standard library to have more package structure.
    • Reason: there are too many modules to keep a flat hierarchy.

Open Issues

  • L += x and L.extend(x) are equivalent. No, they are not. The former creates a new list without modifying the original list (which other people might have references to). The latter modifies the original list.

  • Can the parameter order of the insert method be changed so the the index parameter is optional and list.append may be removed?

  • If only Exception subclasses can be raised 9], should the raise statement be kept? Could x(y).raise() be used instead?

  • Are repr() and str() both needed? 1]

  • Should globals(), locals() and vars() be removed? 1]

  • Should there be a keyword for allowing the shadowing of built-ins?
  • Should injecting into another module's global namespace be prevented?

  • If line continuations (\) are removed from the language 1], what should be done about the instances where statements do not allow parentheses? Furthermore, the Python style guide 11] recommends their usage in some cases.

  • Should __cmp__ (and possibly cmp()) be removed? 8]

    • Reason: TOOWTDI and rich comparisons are another way.

  • Should list comprehensions be equivalent to passing a generator expression to list()?

    • Reason: they are essentially the same and it would remove edge-case differences between them.

  • With a new string substitution scheme 14], will old-style (%(var)s) substitutions be removed?

  • There are things in the string module that I think belong there, for example string.letters and string.digits. I don't think that all the string manipulations that we might include with the standard libraries need to be in the core interpreter (any more than I would condone putting the regular expression engine into the core). -- JimD

  • Should a with (or using) statement be added? 10] 19] 

       1 with self:
   2     .foo = [1, 2, 3]
   3     .bar(4, .foo)

References

Python3.0 (last edited 2011-04-08 16:42:51 by ip-109-90-196-137)

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