[Python-Dev] Internal representation of strings and Micropython

[Terry Reedy]

On 6/4/2014 5:14 PM, Paul Sokolovsky wrote:

> That said, and unlike previous attempts to develop a small Python
> implementations (which of course existed), we're striving to be exactly
> a Python language implementation, not a Python-like language
> implementation. As there's no formal, implementation-independent
> language spec, what constitutes a compatible language implementation is
> subject to opinions, and we welcome and appreciate independent review,
> like this thread did.
>
>> Realistically, most Python code that works on Python 3.4 won't work
>> on Micropython (for various reasons, not just the string behavior)
>> and neither does it need to.
>
> That's true. However, as was said, we're striving to provide a
> compatible implementation, and compatibility claims must be validated.
> While we have simple "in-house" testsuite, more serious compatibility
> validation requires running a testsuite for reference implementation
> (CPython), and that's gradually being approached.

I would call what you are doing a 'Python 3.n subset, with limitations', 
where n should be a specific number, which I would urge should be at 
least 3, if not 4 ('yield from'). To me, that would mean that every 
Micropython program (that does not use a clearly non-Python addon like 
inline assembly) would run the same* on CPython 3.n. Conversely, a 
Python 3.n program should either run the same* on MicroPython as 
CPython, or raise. What most to avoid is giving different* answers.

*'same' does not include timing differences or normal float variations 
or bug fixes in MicroPython not in CPython.

As for unicode: I would see ascii-only (very limited codepoints) or bare 
utf-8 (limited speed == expanded time) as possibly fitting the 
definition above. Just be clear what the limitations are. And accept 
that there will be people who do not bother to read the limitations and 
then complain when they bang into them.

PS. You do not seem to be aware of how well the current PEP393 
implementation works. If you are going to write any more about it, I 
suggest you run Tools/Stringbench/stringbench.py for timings.

-- 
Terry Jan Reedy