Well, I finally ran into a Python Unicode problem, sort of

[Ned Batchelder]

On Monday, July 4, 2016 at 10:36:54 AM UTC-4, BartC wrote:
> On 04/07/2016 13:47, Ned Batchelder wrote:
> > On Monday, July 4, 2016 at 6:05:20 AM UTC-4, BartC wrote:
> >> On 04/07/2016 03:30, Steven D'Aprano wrote:
> 
> >>> You're still having problems with the whole Python-as-a-dynamic-language
> >>> thing, aren't you? :-)
> 
> >> Most Pythons seem to pre-compile code before executing the result. That
> >> pre-compilation requires that operators and precedences are known in
> >> advance and the resulting instructions are then hard-coded before execution.
> >
> > This is the key but subtle point that all the discussion of parser mechanics
> > are missing: Python today needs no information from imported modules in
> > order to compile a file.  When the compiler encounters "import xyzzy" in
> > a file, it doesn't have to do anything to find or read xyzzy.py at compile
> > time.
> 
> Yeah, there's that small detail. Anything affecting how source is to be 
> parsed needs to known in advance.
> 
> > If operators can be invented, they will only be useful if they can be
> > created in modules which you then import and use.  But that would mean that
> > imported files would have to be found and read during compilation, not
> > during execution as they are now.
> >
> > This is a huge change.
> 
> I've used a kind of 'weak' import scheme elsewhere, corresponding to C's 
> '#include'.
> 
> Then the textual contents of that 'imported' module are read by the 
> compiler, and treated as though they occurred in this module. No new 
> namespace is created.
> 
> I think that could work in Python provided whatever is defined can 
> tolerate having copies redefined in each module that includes the same 
> file. Anything that is defined once and is never assigned to nor 
> modified for example.

You are hand-waving over huge details of semantics that are very important
in Python.  For example, it is very important not to have copies of
classes.  Importing a module must produce the same module object
everywhere it is imported, and the classes defined in the module must
be defined only once.

This is what makes catching exceptions work (because it is based on an
exception being an instance of a particular class), and what makes
class attributes shared among all the instances of the class.

--Ned.