QUERY · ISSUE

Method Resolution Order (MRO) is not compliant

openby pfalconopened 2014-04-28updated 2024-08-28

py-core

uPy currently implements depth-first MRO, which is equivalent to one used pre-Python2.2.
References:

http://python-history.blogspot.com/2010/06/method-resolution-order.html
https://www.python.org/download/releases/2.3/mro/

CANDIDATE · ISSUE

unix: dir() of a subclass instance does not show superclass methods

closedby peterhinchopened 2017-10-18updated 2018-02-19

This behaviour differs from CPython. Apologies if this is by design:

class FooSub():
    def bar(self):
        pass
 
class Foo(FooSub):
    def rats():
        pass
 
foo = Foo()
dir(foo)

Outcome:

['__module__', 'rats', '__qualname__']

Tab completion also fails to access bar().

Assessment

Q Qwen · high

Both issues involve inheritance and method resolution in MicroPython's type system, but they are distinct bugs. Issue #525 is about the MRO algorithm being depth-first instead of C3 linearization — affecting which method is called in diamond/multiple inheritance scenarios. Issue #3376 is about dir() failing to walk the inheritance chain at all, omitting superclass methods from introspection output. The dir() bug would exist independently of whether MRO is C3 or depth-first; it's a separate traversal issue in the dir() builtin implementation. They share affected code area (py/objtype) but have different root causes and fixes.

Suggested action

Keep both issues open. The dir() traversal bug in #3376 should be fixed independently of the MRO algorithm fix in #525. Cross-reference them for context when working on the inheritance subsystem.

Method Resolution Order (MRO) is not compliant

unix: dir() of a subclass instance does not show superclass methods

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