No seamless workaround for missing descriptor support

[cefn]

There's a fundamental contrast in the build flags between CircuitPython and Micropython seen here...

At https://github.com/micropython/micropython/blob/6e675c1baaf0de0d56a2345376d6b5600bfab3aa/py/mpconfig.h the default is set, which applies to official pyboard and esp8266 builds.

// Whether to support descriptors (__get__ and __set__)
// This costs some code size and makes all load attrs and store attrs slow
#ifndef MICROPY_PY_DESCRIPTORS
#define MICROPY_PY_DESCRIPTORS (0)
#endif

Versus the build flags for esp8266 and atmel-samd in CircuitPython

cefn@cefn-artful-thinkpad:~/Documents/shrimping/clients/adafruit/git/circuitpython-latest$ grep -rin MICROPY_PY_DESCRIPTORS .
./ports/atmel-samd/mpconfigport.h:56:#define MICROPY_PY_DESCRIPTORS      (1)
./ports/esp8266/mpconfigport.h:43:#define MICROPY_PY_DESCRIPTORS      (1)

While perhaps an average user wouldn't be reliant on descriptors, some libraries use them or encourage their use, for example adafruit_register fundamentally depends on descriptors, meaning that e.g. the BNO055 library and RFM69 libraries intended to be used in #2 cannot be made to work seamlessly on Micropython simply by making compatible I2C or SPI objects available.

The list of libraries affected in this way includes at least...

• adafruit_register
• adafruit_bno055
• adafruit_tlc59711
• adafruit_rfm69.py
• adafruit_thermal_printer

This list is based on searching for libraries using __get__() or __set__() within the Adafruit CircuitPython Bundle.

Since it doesn't trigger a load-time error, it may be feasible to monkey-patch classes such as BNO055 with property accessors to hide the descriptor logic, a step performed before using any of the constructors. However, this step would have to be explicit in any Micropython-hosted use of said CircuitPython libraries, or a separate bundle could be distributed in which descriptor logic has been substituted.

[tannewt]

I don't think we should change our libraries for this. Data descriptors simplify the drivers a bunch.

Would you mind opening an issue in MicroPython's repo for them to enable it? They should be interested in having our libraries compatible. I can follow up on it as well.

[cefn]

I'm taking Damien's inline comment...

// This costs some code size and makes all load attrs and store attrs slow

...and the statements at https://github.com/micropython/micropython/wiki/Differences to mean they have already decided to exclude it by default, so I think the debate has been had once and settled in favour of performance and resource-efficiency, given there are always substitute language structures.

Do you think we should open it as an issue in any case to record the decision?

BTW I am not proposing that libraries are changed. Rather that people running on Micropython would have to run a post-load monkey-patching operation to switch descriptors for properties on classes where they are found. This would be after import and before use, and not require any code-changes to the module source. Not sure when and how this strategy might fail, though. E.g. are frozen-modules any different in terms of dynamic manipulation. It might be a crazy thought until I've worked through it.

[tannewt]

I think opening an issue is still worth while. That decision was made before we had 50+ libraries. :-) Determining the code size increase would be a good piece of info to have too.

What would they switch the descriptors to? Properties are implemented using data descriptors.

Frozen modules won't be an issue because we're assuming its a MicroPython build. mpy files are identical to py files after load.

[cefn]

What would they switch the descriptors to? Properties are implemented using data descriptors.

I'm just picking up on the https://github.com/micropython/micropython/wiki/Differences comment;
"So far, we were able to implement all native Python features (like properties) without explicit descriptors."

If it's not been covered again recently I'll open an issue.

[cefn]

Ancient discussion of strategy for implementing properties at micropython/micropython#474 and
https://github.com/micropython/micropython/blob/6e675c1baaf0de0d56a2345376d6b5600bfab3aa/py/mpconfig.h shows properties configured by default across all current builds, so the property patching strategy should be feasible if no official descriptor support (or while waiting for it).

[cefn]

You can find the issue on enabling descriptor support on official images as recently raised at https://github.com/micropython/micropython/issues?utf8=%E2%9C%93&q=is%3Aissue+descriptor

[tannewt]

Upstream issue is micropython/micropython#3644 and I've subscribed to it. Thanks!

[makermelissa]

Closing as it appears descriptors were added.