Should __init__() call the parent class’s __init__()?

If you need something from super’s __init__ to be done in addition to what is being done in the current class’s __init__, you must call it yourself, since that will not happen automatically. But if you don’t need anything from super’s __init__, no need to call it. Example:

>>> class C(object):
        def __init__(self):
            self.b = 1


>>> class D(C):
        def __init__(self):
            super().__init__() # in Python 2 use super(D, self).__init__()
            self.a = 1


>>> class E(C):
        def __init__(self):
            self.a = 1


>>> d = D()
>>> d.a
1
>>> d.b  # This works because of the call to super's init
1
>>> e = E()
>>> e.a
1
>>> e.b  # This is going to fail since nothing in E initializes b...
Traceback (most recent call last):
  File "<pyshell#70>", line 1, in <module>
    e.b  # This is going to fail since nothing in E initializes b...
AttributeError: 'E' object has no attribute 'b'

__del__ is the same way, (but be wary of relying on __del__ for finalization – consider doing it via the with statement instead).

I rarely use __new__. I do all the initialization in __init__.