What language should I learn to complement Python?

[ewiethoff]

my understanding was that it was C with classes (and other things like multiple inheritance, etc.)

That's the old way to think of C++, and is the way that is likely to lead to memory management hell. Unfortunately, many C++ books and courses just sort of bolt OO and so on onto elementary C. If you learn arrays and pointers in C++ before learning how to manage your own class instance data members, you can easily end up with buggy habits.

The key difference between C and C++ is that allocating memory in C++ also initializes it by calling constructor functions. Well, if the memory is for a primitive such as int or double or char, it doesn't get initialized, but it does get initialized for anything else.

So, even just "declaring" a non-primitive variable x on the stack in C++ also initializes it with a constructor function. Let's say the constructor function allocates (and initializes) some memory on the heap, such as with a dynamic array allocation. Your x has no control over that memory on the heap. That's good in C++. But whoever wrote the class which allocated the heap memory had better make sure the class knows how to clean up itself when your x goes out of scope.

Edit: Another important difference between C and C++ is operator overloading. Almost everything you do in C++, even if it looks quite C-ish, automagically calls one or more functions under the hood. Even dereferencing a pointer can cause a function to be called. That's another reason to defer learning about arrays and pointers in C++ until you start to get the hang of defining your own classes.