aiorepl: Can't assign top-level object attributes, but lower level objects work

[sandyscott]

Apologies if the title isn't clear, hopefully this example will explain my issue:

So I'm using aiorepl to help make certain bits of my code interactive, and I pass object.__dict__ to aiorepl.task().

What's confused me is which bits of the object I can actually modify - basically I only seem to be able to assign values to properties of sub-objects - assigning a value to a property of the top level object just results in a TypeError. In this example the only assignment that works is to inner.a

import aiorepl
import uasyncio as asyncio

class innerClass:
    a = 1
    
class outerClass:
    b = 2
    c = innerClass()
    def __init__(self):
        self.d = 3
        self.inner = innerClass()

def main():
    obj = outerClass()
    asyncio.create_task(aiorepl.task(obj.__dict__))
    while True:
        await asyncio.sleep(0)

asyncio.run(main())

Now to run it and try to access the properties of the outerClass and innerClass objects:

Starting asyncio REPL...
--> b
NameError: name 'b' isn't defined
--> c
NameError: name 'c' isn't defined
--> d
3
--> inner
<innerClass object at 2000ba00>
--> inner.a
10
--> d = 10
TypeError: 
--> inner.a = 11
--> inner.a
11

I might not be understanding __dict__ properly, but I think it would help if there was a way of making this behave a bit more intutively - ie. I'd like to pass an object (maybe wrapped in some function to pull out the relevant bits) and I can then access the object like you would at a normal python terminal - read/write access to all the properties, and can call methods.

[jimmo]

hi @sandyscott -- Interesting question! The ability to set the globals dict was mostly intended to be passed a module's dict.

In MicroPython the dictionary returned by __dict__ on a class instance is read-only. (This is different to CPython). It's not a copy, it references the underlying members dict, but it's marked as read-only.

b and c aren't available because they aren't part of the instance's __dict__ (this is the same in CPython).

Setting nested members works because it's a regular read-only lookup of the first level, then eval() is taking care of the assignment.

In theory you could construct a dict-like object (that implements __setitem__ etc) that wraps an instance type, but unfortunately in MicroPython, the dict passed to eval (used internally in aiorepl) needs to be an actual dict.

I suspect the best workaround for your use case is to make a very simple wrapper dict, i.e. aiorepl.task({"obj": obj }) which would allow you to do --> obj.d = 10 etc. Not quite so convenient but I haven't been able to think of a better workaround.

[sandyscott]

Hi @jimmo.

Thanks for the detailed response - after a bit more digging I realise __dict__ is somewhat more of a minefield than I'd realised. I also found a roughly equivalent workaround (wrapping it in a minimal object, then using __dict__) but your way is neater.

I'm satisfied that my problem is solved, if you or another maintainer thinks this is worth adding to the documentation, I created PR 687 which adds an extra paragraph to cover this use case.