Abstract

Some ideas are just bad. While some thoughts on Python evolution are constructive, some go against the basic tenets of Python so egregiously that it would be like asking someone to run in a circle: it gets you nowhere, even for Python 3000, where extraordinary proposals are allowed. This PEP tries to list all BDFL pronouncements on Python 3000 that refer to changes that will not happen and new features that will not be introduced, sorted by topics, along with a short explanation or a reference to the relevant thread on the python-3000 mailing list.

If you think you should suggest any of the listed ideas it would be better to just step away from the computer, go outside, and enjoy yourself. Being active outdoors by napping in a nice patch of grass is more productive than bringing up a beating-a-dead-horse idea and having people tell you how dead the idea is. Consider yourself warned.

Core language

• Python 3000 will not be case-insensitive.

• Python 3000 will not be a rewrite from scratch.

  It will also not use C++ or another language different from C as implementation language. Rather, there will be a gradual transmogrification of the codebase. There's an excellent essay by Joel Spolsky explaining why: http://www.joelonsoftware.com/articles/fog0000000069.html

• self will not become implicit.

  Having self be explicit is a good thing. It makes the code clear by removing ambiguity about how a variable resolves. It also makes the difference between functions and methods small.

  Thread: "Draft proposal: Implicit self in Python 3.0" http://mail.python.org/pipermail/python-dev/2006-January/059468.html

• lambda will not be renamed.

  At one point lambda was slated for removal in Python 3000. Unfortunately no one was able to come up with a better way of providing anonymous functions. And so lambda is here to stay.

  But it is here to stay as-is. Adding support for statements is a non-starter. It would require allowing multi-line lambda expressions which would mean a multi-line expression could suddenly exist. That would allow for multi-line arguments to function calls, for instance. That is just plain ugly.

  Thread: "genexp syntax / lambda", http://mail.python.org/pipermail/python-3000/2006-April/001042.html

• Python will not have programmable syntax.

  Thread: "It's a statement! It's a function! It's BOTH!", http://mail.python.org/pipermail/python-3000/2006-April/000286.html

• There won't be a syntax for zip()-style parallel iteration.

  Thread: "Parallel iteration syntax", http://mail.python.org/pipermail/python-3000/2006-March/000210.html

• Strings will stay iterable.

  Thread: "Making strings non-iterable", http://mail.python.org/pipermail/python-3000/2006-April/000759.html

• There will be no syntax to sort the result of a generator expression or list comprehension. sorted() covers all use cases.

  Thread: "Adding sorting to generator comprehension", http://mail.python.org/pipermail/python-3000/2006-April/001295.html

• Slices and extended slices won't go away (even if the __getslice__ and __setslice__ APIs may be replaced) nor will they return views for the standard object types.

  Thread: Future of slices http://mail.python.org/pipermail/python-3000/2006-May/001563.html

• It will not be forbidden to reuse a loop variable inside the loop's suite.

  Thread: elimination of scope bleeding of iteration variables http://mail.python.org/pipermail/python-dev/2006-May/064761.html

• The parser won't be more complex than LL(1).

  Simple is better than complex. This idea extends to the parser. Restricting Python's grammar to an LL(1) parser is a blessing, not a curse. It puts us in handcuffs that prevent us from going overboard and ending up with funky grammar rules like some other dynamic languages that will go unnamed, such as Perl.

• No braces.

  This is so obvious that it doesn't need a reference to a mailing list. Do from __future__ import braces to get a definitive answer on this subject.

• No more backticks.

  Backticks (`) will no longer be used as shorthand for repr -- but that doesn't mean they are available for other uses. Even ignoring the backwards compatibility confusion, the character itself causes too many problems (in some fonts, on some keyboards, when typesetting a book, etc).

  Thread: "new operators via backquoting", http://mail.python.org/pipermail/python-ideas/2007-January/000054.html

• Referencing the global name foo will not be spelled globals.foo. The global statement will stay.

  Threads: "replace globals() and global statement with global builtin object", http://mail.python.org/pipermail/python-3000/2006-July/002485.html, "Explicit Lexical Scoping (pre-PEP?)", http://mail.python.org/pipermail/python-dev/2006-July/067111.html

• There will be no alternative binding operators such as :=.

  Thread: "Explicit Lexical Scoping (pre-PEP?)", http://mail.python.org/pipermail/python-dev/2006-July/066995.html

• We won't be removing container literals. That is, {expr: expr, ...}, [expr, ...] and (expr, ...) will stay.

  Thread: "No Container Literals", http://mail.python.org/pipermail/python-3000/2006-July/002550.html

• The else clause in while and for loops will not change semantics, or be removed.

  Thread: "for/except/else syntax" http://mail.python.org/pipermail/python-ideas/2009-October/006083.html

Builtins

• zip() won't grow keyword arguments or other mechanisms to prevent it from stopping at the end of the shortest sequence.

  Thread: "have zip() raise exception for sequences of different lengths", http://mail.python.org/pipermail/python-3000/2006-August/003338.html

• hash() won't become an attribute since attributes should be cheap to compute, which isn't necessarily the case for a hash.

  Thread: "hash as attribute/property", http://mail.python.org/pipermail/python-3000/2006-April/000362.html

Standard types

• Iterating over a dictionary will continue to yield the keys.

  Thread: "Iterating over a dict", http://mail.python.org/pipermail/python-3000/2006-April/000283.html

  Thread: have iter(mapping) generate (key, value) pairs http://mail.python.org/pipermail/python-3000/2006-June/002368.html

• There will be no frozenlist type.

  Thread: "Immutable lists", http://mail.python.org/pipermail/python-3000/2006-May/002219.html

• int will not support subscripts yielding a range.

  Thread: "xrange vs. int.__getslice__", http://mail.python.org/pipermail/python-3000/2006-June/002450.html

Coding style

• The (recommended) maximum line width will remain 80 characters, for both C and Python code.

  Thread: "C style guide", http://mail.python.org/pipermail/python-3000/2006-March/000131.html

Interactive Interpreter

• The interpreter prompt (>>>) will not change. It gives Guido warm fuzzy feelings.

  Thread: "Low-hanging fruit: change interpreter prompt?", http://mail.python.org/pipermail/python-3000/2006-November/004891.html

Copyright

This document has been placed in the public domain.