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Now your class C can't necessarily be used in a multiple inheritance hierarchy with some other class D, and a class E that inherits from C and D, as C hardcodes

Now your class C can't necessarily be used in a multiple inheritance hierarchy with some other class D, and a class E that inherits from C and D, as C hardcodes what its parents are. Python uses the C3 MRO algorithm to traverse all relevant classes in your hierarchy when you religiously use the super builtin. https://www.python.org/download/releases/2.3/mro/ https://www.python.org/download/releases/2.3/mro/ But; multiple inheritance is a beast in any language due to its complexity and bringing it up in a discussion of "magic" that python exposes beginners to is specious. It's true that C++ doesn't have this problem, because it has no super keyword and you must explicitly delegate everything, but also introduces the problem that you can have multiple instances of a base class and so has added complexity, virtual inheritance, to solve THAT problem. And tons of languages have a problem where omitting a call to "super" is logically required is not statically diagnosable.

renewiltord 6y ago
Ohhh, that makes sense, because any later child will need to know that A and B are C's parents! Okay, thanks!
- theg5prank 6y ago
  That, and: I forgot to mention that not using the super builtin can also lead to unintentionally calling a method twice or more for the same base class in a diamond situation (note that with new-style classes, all multiple inheritance has at least one "diamond" class, often object, but people normally do not delegate to object for obvious reasons; you can imagine a base class Z in this example that A and B inherit from instead, if you wish). So, not using the super builtin can result in both delegating to a superclass' implementation too much, and not at all! This is a problem with multiple inheritance that Python actually solves; virtual inheritance doesn't touch it. Note that `object` being the root of the class hierarchy implies that you must have careful coordination between all classes in a multiple inheritance hierarchy to determine, for a particular method, when subclasses may/must delegate to super, what the arguments to the method are, and even what the argument names are in some cases! You can't just go glomming classes together and expect it to go well unless you know the classes either don't use the same method names or agree very carefully on what the delgatable interfaces are.
  - renewiltord 6y ago
    Oh, ah yes, that's good. With the A.__init(self) approach you'd overcall in a diamond-pattern. Okay, I'm convinced.
mehrdadn 6y ago
> It's true that C++ doesn't have this problem, because it has no super keyword and you must explicitly delegate everything It's emphatically not "having a super keyword" or not having it. That's a red herring. Visual C++ has __super and yet it doesn't suffer from this: it errors with "ambiguous call to overloaded function" when there are multiple candidates. There's a lot more I could say about this (frankly the issue I outlined just scratch the surface of a deeper problem in Python), but this is diverting the discussion. Nobody even said C++ is simple or somehow easier to learn than Python in the first place; I was just pointing out an insidious issue in Python, and frankly, it could've been done better without any need to emulate C++'s approach at all. (Exercise for the reader: suggest improvements.)
- theg5prank 6y ago
  > It's emphatically not "having a super keyword" or not having it. That's a red herring. Visual C++ has __super and yet it doesn't suffer from this: it errors with "ambiguous call to overloaded function" when there are multiple candidates What's your point about this nonstandard extension? My point is that C++ doesn't have the problem of classes not written to be part of a multiple inheritance hierarchy delegating somewhere unexpected because, by design, it doesn't attempt to solve the same problems that Python is. If anything that this nonstandard extension doesn't work in multiple inheritance is agreeing with the points I'm making. > There's a lot more I could say about this (frankly the issue I outlined just scratch the surface of a deeper problem in Python), but this is diverting the discussion. Nobody even said C++ is simple or somehow easier to learn than Python in the first place; I was just pointing out an insidious issue in Python, You were the one who brought up C++! (EDIT: this was in a cousin comment.) My point is that different languages navigate this thorny landscape in different ways, but the way in which Python does isn't as haphazard as you are suggesting. > Exercise for the reader: suggest improvements Perhaps being part of a multiple inheritance hierarchy is sharp and uncommon enough that it should be opt-in. What are yours?
  - mehrdadn 6y ago
    > What's your point about this nonstandard extension? My point was what I said: you can have your cake and eat it too. You claimed the issue was due to a lack of a super keyword and I showed you it would not occur even if C++ had super. > You were the one who brought up C++! I "brought it up" to illustrate it does one particular thing better than Python. Not to claim it does everything better than Python. If you want a simple, beginner-friendly language, avoid C++ like the plague. > What are yours? Idk, for starters maybe produce a warning when multiple inheritance occurs and one of the __init__s in the hierarchy doesn't have an obvious call super().__init__.

renewiltord 6y ago

Ohhh, that makes sense, because any later child will need to know that A and B are C's parents! Okay, thanks!

theg5prank 6y ago
That, and: I forgot to mention that not using the super builtin can also lead to unintentionally calling a method twice or more for the same base class in a diamond situation (note that with new-style classes, all multiple inheritance has at least one "diamond" class, often object, but people normally do not delegate to object for obvious reasons; you can imagine a base class Z in this example that A and B inherit from instead, if you wish). So, not using the super builtin can result in both delegating to a superclass' implementation too much, and not at all! This is a problem with multiple inheritance that Python actually solves; virtual inheritance doesn't touch it. Note that `object` being the root of the class hierarchy implies that you must have careful coordination between all classes in a multiple inheritance hierarchy to determine, for a particular method, when subclasses may/must delegate to super, what the arguments to the method are, and even what the argument names are in some cases! You can't just go glomming classes together and expect it to go well unless you know the classes either don't use the same method names or agree very carefully on what the delgatable interfaces are.
- renewiltord 6y ago
  Oh, ah yes, that's good. With the A.__init(self) approach you'd overcall in a diamond-pattern. Okay, I'm convinced.

mehrdadn 6y ago

> It's true that C++ doesn't have this problem, because it has no super keyword and you must explicitly delegate everything It's emphatically not "having a super keyword" or not having it. That's a red herring. Visual C++ has __super and yet it doesn't suffer from this: it errors with "ambiguous call to overloaded function" when there are multiple candidates. There's a lot more I could say about this (frankly the issue I outlined just scratch the surface of a deeper problem in Python), but this is diverting the discussion. Nobody even said C++ is simple or somehow easier to learn than Python in the first place; I was just pointing out an insidious issue in Python, and frankly, it could've been done better without any need to emulate C++'s approach at all. (Exercise for the reader: suggest improvements.)

theg5prank 6y ago
> It's emphatically not "having a super keyword" or not having it. That's a red herring. Visual C++ has __super and yet it doesn't suffer from this: it errors with "ambiguous call to overloaded function" when there are multiple candidates What's your point about this nonstandard extension? My point is that C++ doesn't have the problem of classes not written to be part of a multiple inheritance hierarchy delegating somewhere unexpected because, by design, it doesn't attempt to solve the same problems that Python is. If anything that this nonstandard extension doesn't work in multiple inheritance is agreeing with the points I'm making. > There's a lot more I could say about this (frankly the issue I outlined just scratch the surface of a deeper problem in Python), but this is diverting the discussion. Nobody even said C++ is simple or somehow easier to learn than Python in the first place; I was just pointing out an insidious issue in Python, You were the one who brought up C++! (EDIT: this was in a cousin comment.) My point is that different languages navigate this thorny landscape in different ways, but the way in which Python does isn't as haphazard as you are suggesting. > Exercise for the reader: suggest improvements Perhaps being part of a multiple inheritance hierarchy is sharp and uncommon enough that it should be opt-in. What are yours?
- mehrdadn 6y ago
  > What's your point about this nonstandard extension? My point was what I said: you can have your cake and eat it too. You claimed the issue was due to a lack of a super keyword and I showed you it would not occur even if C++ had super. > You were the one who brought up C++! I "brought it up" to illustrate it does one particular thing better than Python. Not to claim it does everything better than Python. If you want a simple, beginner-friendly language, avoid C++ like the plague. > What are yours? Idk, for starters maybe produce a warning when multiple inheritance occurs and one of the __init__s in the hierarchy doesn't have an obvious call super().__init__.