For Python subclass, forgetting to call C++ superclass __init__ constructor is painful

[EricCousineau-TRI]

While it is noted here in the docs:
https://pybind11.readthedocs.io/en/stable/advanced/classes.html#overriding-virtual-functions-in-python
it is still sometimes easy to forget. If it were somehow possible, it'd be nice to robustly detect access to unconstructed base classes. (... though it may be a big performance penalty, so I'm fine with this being closed as "Not a Problem")

Example failure case from above:

class Dachschund(Dog):
    def __init__(self, name):
        # Oops!
        self.name = name

    def bark(self):
        return "yap!"

d = Dog("Sir Schnitzel")
d.go(10)  # Nuts!

Had run into it when writing this example, and then felt dumb once I realized what the problem was.

[bstaletic]

Considering that we've merged #2152, can we close this now?

[YannickJadoul]

I say we can.