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    ''If PEP 343 is approved, "as" might not be usable for this.''

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

If you have suggestions or comments for Python 3000, please add them to ["Python3.0Suggestions"].

Core Language Changes

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

    • (With 2.4 released, this is mostly done? -- JimD)

  • Make all strings unicode #d 4, and have a separate bytes #b 2 type. #m 13

  • 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), writeline(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.)

    • 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

  • 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 use an "as" keyword for this #o 15 and for adaptation #p 16: 

         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     ...

      • If PEP 343 is approved, "as" might not be usable for this.

    • GvR suggested the syntax #q 17: 

         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

  • Make as a true keyword. #g 7

  • Make True and False keywords. #f 6

    • Reason: make assignment to them impossible.
  • Make true division default.
  • Raise an exception when making comparisons between two incongruent types (other than equality and inequality.)
    • Reason: such comparisons do not make sense and are especially confusing to new users of Python.

  • Require that all exceptions inherit a common base classs. #i 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 #r 18

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

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

       1 if expression: statement
   2 
   3 # -->
   4 
   5 if expression:
   6     statement

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.

      • 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

  • Remove types module.

    • Instead: use the types in __builtins__.

  • Remove other deprecated modules. #c 3

  • Remove sys.exc_type. #a 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.

  • 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)?

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

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

  • Should globals(), locals() and vars() be removed? #a 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 #a 1, what should be done about the instances where statements do not allow parentheses? Furthermore, the Python style guide #k 11 recommends their usage in some cases.

  • Should __cmp__ (and possibly cmp()) be removed? #h 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 #n 14, will old-style (%(var)s) substitutions be removed?

  • Should a with statement be added? Not like this! #j 10 #s 19 #t 20 

       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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