This page lists features that GvR has mentioned as goals for Python 3.0. This page has been consolidated into PEP 3000; the PEP is more up-to-date and is actively maintained. #e 5

(Another list is at PythonThreeDotOh, but it incorporates items that GvR has never talked about.)

Core Language Changes

• Remove distinction between int and long types. #d 4

• Make all strings unicode #d 4, and have a separate bytes #b 2 type.

• Replace all old-style classes. #d 4

• Make the exec statement a function (again.) #a 1

• Make the print statement a function. (write(x,y,z), writeln(x,y,z)) #a 1

• 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.)

• Add a with statement:

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

• Remove `x`. #a 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 the lambda statement. #a 1 #d 4

  • Instead: use a local function.

  • Reason: lambda supports only one statement.

• Remove support for string exceptions. #a 1

  • Instead: use a class.
• Perhaps have optional declarations for static typing.

  • One suggestion is to [http://mail.python.org/pipermail/python-dev/2004-February/042795.html use an "as" keyword for this] and for adaptation ([http://www.python.org/peps/pep-0246.html PEP 246]):

       1 # "x as y" means: adapt x to the y protocol
       2 
       3 def foo (a as int, b as float) as float:
       4     a2 = a as float  # Same as: adapt(a, float)
       5     ...
    

• Make list comprehensions equivalent to passing a generator expression to list()

  • Reason: essentially the same and removes edge-case differences between the two

• as a keyword #g 7

• Have True and False be keywords #f 6

  • Reason: stop assignment to them
• True division becomes default

• Remove __cmp__ (and possibly cmp() ) #h 8

  • Reason: TOOWTDI and rich comparisons are another way

• Raise exception when comparing two heterogeneous types with operators other than == and !=

  • Reason: comparisons do not make sense

• Automatically have types compare as not equal when types are heterogeneous #i 9

  • Reason: equality does not make sense between heterogeneous types

• Exceptions inherit from common base class #j 10

  • Reason: forces use of classes as objects raised by exceptions; simplifies implementation

Built-In Changes

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

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

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

• Remove coerce() as it is obsolete. #a 1

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

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

• Remove apply(). #a 1

  • Instead: use f(*args, **kw).

• Remove xrange(). #a 1 #d 4

  • Instead: use range().

• Remove map() and filter(). #a 1 #d 4

  • Instead: use list comprehensions.

• Remove reduce(). #a 1

  • Instead: use a loop.

• Remove callable(). #a 1

  • Instead: catch the exception.

• Remove buffer(). #a 1 #b 2

  • Instead: use new bytes type.

• Remove raw_input(). #a 1

  • Instead: use sys.stdin.readline().

• Remove input(). #a 1

  • Instead: use eval(sys.stdin.readline()).

• Remove execfile() and reload(). #a 1

  • Instead: use exec().

Standard Library Changes

• Remove string module. #c 4

  • Instead: use string methods.

• Remove other deprecated modules. #c 3

• Remove sys.exc_type. #a 1

  • Instead: use sys.exc_info.

  • Reason: it is not thread safe.
• Reorganize with more package structure
  • Reason: too many modules to have in a flat hierarchy

Unresolved Issues

• L += x and L.extend(x) are equivalent.

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

• Should the raise x, y syntax be removed as to favor raise x(y)?

• Are repr() and str() both needed? #a 1

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

• Keyword for allowing shadowing of built-ins?
• Prevent injecting into another modules global namespace?

References

• Anchor(a) [1] Python Regrets: http://www.python.org/doc/essays/ppt/regrets/PythonRegrets.pdf

• Anchor(b) [2] PEP 296 -- Adding a bytes Object Type: http://python.org/peps/pep-0296.html

• Anchor(c) [3] PEP 4 -- Deprecation of Standard Modules: http://python.org/peps/pep-0004.html

• Anchor(d) [4] PyCon 2003 State of the Union Address: http://www.python.org/doc/essays/ppt/pycon2003/pycon2003.ppt

• Anchor(e) [5] PEP 3000 -- Python 3.0 Plans: http://python.org/peps/pep-3000.html

• Anchor(f) [6] "Constancy of None" thread -- http://mail.python.org/pipermail/python-dev/2004-July/046294.html

• Anchor(g) [7] " "as" to be a keyword?" thread -- http://mail.python.org/pipermail/python-dev/2004-July/046316.html

• Anchor(h) [8] "lists vs. tuples" thread -- http://mail.python.org/pipermail/python-dev/2003-March/034073.html

• Anchor(i) [9] another email from "lists vs. tuples" thread -- http://mail.python.org/pipermail/python-dev/2003-March/034074.html

• Anchor(j) [10] "Exceptional inheritance patterns" thread -- http://mail.python.org/pipermail/python-dev/2004-August/047114.html