Multiple inheritance and a broken super() chain

[Alan Gauld]

On 03/07/2023 19:39, Chris Angelico via Python-list wrote:
> On Tue, 4 Jul 2023 at 03:39, Peter Slížik via Python-list
>> The legacy code I'm working with uses a classic diamond inheritance. 

> What happens when Top is initialized twice? This seems like a problem
> waiting to happen, and when you moved to using super(), you more than
> likely simplified things and fixed things.

Slightly off topic but I wonder how many real world problems
people have experienced having the top of a diamond initialized
twice? The reason I ask is that I ran a maintenance team for
about 5 years (early 1990s) working on various OOP projects using MI;
in Lisp Flavors, C++(*) and a homebrew variant of C that supported MI.
In that time I don't recall ever having problems with top objects
being initialized twice (apart from redundant execution of code
of course).

In most cases the top object was so abstract that its init()/constructor
was only doing generic type stuff or opening database sessions/networks
etc which got lost and tidied up by garbage collectors.

So I'm curious about how big this "big problem with MI" is in
practice. I'm sure there are scenarios where it has bitten folks
but it never (or very rarely) occurred in our projects. (Of
course, being maintenance programmers, the problems may have
been ironed out before the code ever reached us! But that
wasn't usually the case...)

(*) C++ is the odd one out because it doesn't have GC, but then
neither does it have an Object superclass so very often MI in C++
does not involve creating diamonds! And especially if the MI
style is mixin based.

-- 
Alan G
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