[Python-ideas] Custom string prefixes

[Andrew Barnert]

On May 29, 2013, at 22:21, Eric Snow <ericsnowcurrently at gmail.com> wrote:

> Now, give a twist to this idea of some stable `literal -> contstant`
> operation. Consider a new syntax or built-in function for indicating
> that, at compile-time, an expression should be considered equivalent
> to the literal to which it evaluates.  Then the compiler would be free
> to substitute the literal for the expression and store the literal in
> the bytecode/constants/pyc file.  From then on that expression would
> not be evaluated at run-time anymore.  Of course, the expression would
> have to be entirely literal-based and evaluate to a literal.

So you're suggesting that instead of C++11-style string prefixes, we should have C++11-style constexpr.

I realize your ultimate conclusion was that we probably don't need _either_ feature. But still, it's amazing how C++11-ish this discussion is getting. Which may be a good hint that (as you suggest) this feature isn't a good fit for Python. 

Unless someone has a way of doing it through compile-time templates, of course. :)

> The catch is that the compiler would have to evaluate the expression,
> which would probably add disproportionate complexity to the compiler.

I don't think it's that bad; the compiler just has to make a call to a PyEval* function.

Also, given that your proposal is that it be explicitly an optional optimization that the compiler is free to ignore means there's an even more trivial implementation...