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

Thomas Wouters thomas@xs4all.net
Mon, 28 Aug 2000 14:38:13 +0200

On Mon, Aug 28, 2000 at 05:54:13AM -0500, Guido van Rossum wrote:

> 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.

Hmm. I'm not really sure. I think it's nice to be able to use 'object.print', and it would be, well, inconsistent, not to allow 'module.print' (or module.exec, for that matter), but I realize how confusing it can be.

Perhaps generate a warning ? :-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!

Ahh, yes. I knew there had to be a list of keywords, but I was too tired to go haunt for it, last night ;)

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

_unresname; 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' unresname parameters ':' suite trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' unresname

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

I tried this before, a week or two ago, but it was too much of a pain. The nodes get tossed around no end, and tracking down where they are STR()'d and TYPE()'d is, well, annoying ;P I tried to hack around it by making STR() and CHILD() do some magic, but it didn't quite work. I kind of gave up and decided it had to be done in the metagrammar, which drove me insane last night ;-) and then decided to 'prototype' it first.

Then again, maybe I missed something. I might try it again. It would definately be the better solution ;)

-- Thomas Wouters <thomas@xs4all.net>

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