[Python-Dev] Python keywords (original) (raw)

Guido van Rossum guido@beopen.com
Mon, 28 Aug 2000 05:54:13 -0500

[Thomas Wouters]

There was a thread here a few weeks ago (or so, I seem to have misplaced that particular thread :P) about using Python keywords as identifiers in some cases. You needed that ability for .NET-Python, where the specs say any identifier should be possible as methods and attributes, and there were some comments on the list on how to do that (by Guido, for one.)

Well, the attached patch sort-of does that. I tried making it a bit nicer, but that involved editing all places that currently use the NAME-type node, and most of those don't advertise that they're doing that :-S The attached patch is in no way nice, but it does work: >>> class X: ... def print(self, x): ... print "printing", x ... >>> x = X() >>> x.print(1) printing 1 >>> x.print <method X.print of X instance at 0x8207fc4> >>> x.assert = 1 >>> However, it also allows this at the top level, currently: >>> def print(x): ... print "printing", x ...

Initially I thought this would be fine, but on second thought I'm not so sure. To a newbie who doesn't know all the keywords, this would be confusing:

def try(): # my first function ... print "hello" ... try() File "", line 1 try() ^ SyntaxError: invalid syntax

I don't know how best to fix this -- using different syntax for 'def' inside a class than outside would require a complete rewrite of the grammar, which is not a good idea. Perhaps a 2nd pass compile-time check would be sufficient.

which results in some unexpected behaviour: >>> print(1) 1 >>> globals()'print' printing 1

But when combining it with modules, it does work as expected, of course: # printer.py: def print(x, y): print "printing", x, "and", y # >>> import printer >>> printer.print <function print at 0x824120c> >>> printer.print(1, 2) printing 1 and 2 Another plus-side of this particular method is that it's simple and straightforward, if a bit maintenance-intensive :-) But the big question is: is this enough for what you need ? Or do you need the ability to use keywords in all identifiers, including variable names and such ? Because that is quite a bit harder ;-P

I believe that one other thing is needed: keyword parameters (only in calls, not in definitions). Also, I think you missed a few reserved words, e.g. 'and', 'or'. See Lib/keyword.py!

A comment on the patch: wouldn't it be much better to change the grammar to introduce a new nonterminal, e.g. unres_name, as follows:

unres_name; NAME | 'for' | 'if' | 'while' | 'else' | 'elif' | 'def' |
'class' | 'print' | 'del' | 'raise' | 'exec' | 'in' | 'is' | 'from' |
'pass' | 'import' | 'global' | 'assert' | 'return' | 'break' |
'continue' | 'try' | 'except' | 'not' | 'lambda' | 'finally'

and use this elsewhere in the rules:

funcdef: 'def' unres_name parameters ':' suite trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' unres_name

Then you'd have to fix compile.c of course, but only in two places (I think?).

--Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)