On 11/16/2017 4:55 PM, Michael Torrie wrote:
On 11/15/2017 11:16 PM, Saeed Baig wrote:
- Do you guys think it would be a good idea? Why or why not? Do you
think there’s a better way to do it? I’d like to know what others
think about this idea before making any formal submission.
Except for forcing it to be read-only, there's absolutely no difference
between your idea of a constant and a normal module name in Python.
Since Python is a dynamic language, all names have to be looked up at
run time. So there's really no speed benefit to having a special const
syntax. In Python, we normally expect developers to act as consenting
adults. Thus a constant is often denoted by an uppercase name (at least
in the scripts I've seen), similar to C or other languages. We can just
say to developers, please don't rebind a name that's all capitals.
That's it.
The idea of named constants has been proposed before, and rejected
pretty much for the reason you give above.
Constants as you propose really only make sense in statically-typed,
compiled languages where the compiler replaces the constant names with
the values in the compiled code. Doesn't work that way in Python, where
things are interpreted at run time.
CPython, at least, already has anonymous constant objects. Number and
string literals are turned into objects when parsed. I presume that all
implementations do this. Some constant expressions are replaced by
(constant) objects during compiling, instead of when running. For
instance "n = 10 + 3' will run as 'n = 13', and "for lang in ('C',
'Java', 'Python') will have the tuple pre-computed (whereas "for lang in
['C', 'Java', 'Python] will have to construct the list each time run).
--
Terry Jan Reedy
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