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
(At the time of writing there was already such a document #l 12, but it incorporates items that GvR has never talked about.)
Non-GvR sanctioned comments added below by JimD and StevenBethard
I can't help but wonder if there's a better place on this wiki for these comments. --JimD
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:
(Added by GvR, suggested by Bram Cohen.)JimD's suggested syntax:
This seems overly complicated to me, especially for the more common case of catching a single exception. -- StevenBethard
I meant that the except statement would accept either an exception or a sequence of exceptions as its first argument and an identifier as its second argument. It could 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
Add a with statement: #j 10
(I like this, but is the following too ugly for use until then?
.. seems quirky, but it does serve to remove most of the visual cluster of self.this and self.that which seems to be the primary benefit of the with statement.
-- 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.
Make as a true keyword. #g 7
Make True and False keywords. #f 6
- Reason: make assignment to them impossible.
Note that this isn't currently possible due to backwards compatibility concerns; a lot of code trying to support versions of Python before and after True and False were introduced looked something like
If True and False were keywords, this would cause a syntax error. -- StevenBethard
Unless I'm drastically mistaken this code would remain unbroken (though it should specifically catch NameError) because the assignment will not be attempted in any version of Python that already supports True and False -- JimD
- 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.
Require that the first statement of a suite be on its own line. #a 1
I'd like to see argument parsing use iterators instead of tuples when applicable. This would allow code like:
Currently, this code causes an infinite loop because Python's argument parsing mechanism fully expands an iterator into a tuple when used in a *args context as above. When iterators are the standard, I would hope that instead of fully expanding the iterator, only the elements from the iterator necessary to fill positional arguments would be extracted. -- StevenBethard
Dare I even suggest that a ***args form could be used in some bizarre way? Personally I think the idea is unspeakably ugly and can't see any real world use for this.
On the other hand I've often wished for something like: (a, b, *c) = foo.parse(filedescriptor.readline()) which would unpack the first arg into a, the next into b, and the rest into c. This desire is probably the result of years of shell scripting where I routinely use code like ps fax | while read pid x x x cmd args; do ... and don't care if args is empty or contains an interminately long list of items. I'm still not sure I'd seriously recommend it to Python. --JimD
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).
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.
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.
BR(I like having the members like string.letters and string.digits even if the methods have all been integrated into the strings type -- JimD) BR(Would str.letters and str.digits be sufficient for your purposes if they existed? Or is it necessary that there's a separate module for letters and digits? -- StevenBethard)
I'm just saying that there are things in the string module that I think belong there. 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
- Instead: use string methods.
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?
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] Python-Dev -- Constancy of None: http://mail.python.org/pipermail/python-dev/2004-July/046294.html
Anchor(g) [7] Python-Dev -- "as" to be a keyword?: http://mail.python.org/pipermail/python-dev/2004-July/046316.html
Anchor(h) [8] Python-Dev -- lists vs. tuples:
Anchor(i) [9] Python-Dev -- Exceptional inheritance patterns: http://mail.python.org/pipermail/python-dev/2004-August/047114.html
Anchor(j) [10] Python-Dev -- With statement: http://mail.python.org/pipermail/python-dev/2004-March/043545.html
Anchor(k) [11] PEP 8 -- Style Guide for Python Code: http://python.org/peps/pep-0008.html
Anchor(m) [13] PEP 332 -- Byte vectors and String/Unicode Unification: http://python.org/peps/pep-0332.html
Anchor(n) [14] PEP 292 -- Simpler String Substitutions: http://python.org/peps/pep-0292.html
Anchor(o) [15] Python-Dev -- other uses for "as": http://mail.python.org/pipermail/python-dev/2004-February/042795.html
Anchor(p) [16] PEP 246 -- Object Adaption: http://www.python.org/peps/pep-0246.html
Anchor(q) [17] Python-Dev -- Decorators: vertical bar syntax: http://mail.python.org/pipermail/python-dev/2004-August/047424.html