[Python-ideas] relaxing keyword usage restrictions
tjreedy at udel.edu
Fri Sep 9 18:05:52 CEST 2011
On 9/9/2011 3:21 AM, H Krishnan wrote:
> P.S.. Yes, that's valid scheme? So what? Redefining 'define' pretty
> much guarantees that the rest of your program will fail.
> (define define 3)
> (display (* define 5))=> 15
> (define x4)=> FAIL
> The fact that another language allows you to shoot yourself in the
> foot isn't a good argument that Python should allow that too.
> Yes, scheme does not have special syntax for 'keywords' but still allows
> keywords to be overridden.
In the above, 'define' is not a keyword, it is a built-in function or
macro name. Python allows those to be over-ridden too, with the same
list = 3
list(1,2,3) # TypeError: 'int' object is not callable
Because of its simple one-syntax-fits-all-needs design, I do not think
Scheme has or needs functional keywords in the way Python does. For
instance, the class statement, with it 'class' keyword, can be replaced
by a call to the builtin 'type' class. The name 'type' can be
over-ridden just like 'define' above.
Perhaps Scheme has value keywords like Common Lisp (NIL?), I don't know.
"In Common Lisp, the term "keyword" (or "keyword symbol") is used for a
special sort of symbol, or identifier. Unlike other symbols, which
usually stand for variables or functions, keywords are self-quoting and
evaluate to themselves. Keywords are usually used to label named
arguments to functions, and to represent symbolic values."
Python has keyword values None, False, and True. These used to just be
builtin identifiers that could be over-ridden, but were made keywords to
> But nothing (but syntax highlighters)
and the parser -- see my other post and Paul Moore's followup.
> will break in Python by allowing keywords as identifiers,
If you disagree, try changing the grammar to do what you want while
keeping Python an LL(1) language.
> and so it is a less drastic change for Python.
We seem to have different ideas of 'drastic' ;-).
Terry Jan Reedy
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