bpo-27860: clean up ipaddress

[methane]

Patch by Moritz Sichert.

https://bugs.python.org/issue27860

[serhiy-storchaka]

What is faster, _BaseNetwork.__init__() or super().__init__()?

[MoritzS]

In my initial patch I changed this to the super().__init__() on purpose from the version where the base class is mentioned explicitly. Not using the super() version here makes it harder to write subclasses for those classes. Also, I personally think it's better style to use super().

I have not measured it but I don't think that this is a significant speed improvement.

[methane]

Not using the super() version here makes it harder to write subclasses for those classes.

Simple subclass is OK without super(). It helps only complicated subclassing like:

class A(IPv4Network):
    def __init__(self, address):
        super().__init__(address)

class B(_BaseNetwork):
    def __init__(self, address)
        super().__init__(address)

class C(A, B):
    def __init__(self, address):
        super().__init__(address)

In this case, if we don't use super() in IPv4Network, __init__ is called for C -> A -> IPv4Network -> _BaseNetwork (B is skipped)
if we use super(), C -> A -> IPv4Network -> B -> _BaseNetwork.

But note that _BaseNetwork is private class.
Not using super() here doesn't make write subclass of IPv4Network harder.

Also, I personally think it's better style to use super().

I'm +0.1 on super in general.

I have not measured it but I don't think that this is a significant speed improvement.

It seems 3% slowdown.

$ ./python -m perf timeit -s 'from ipaddress import IPv4Network' 'IPv4Network("10.10.1.0/24")'
...
Mean +- std dev: [legacy] 8.96 us +- 0.09 us -> [super] 9.23 us +- 0.07 us: 1.03x slower (+3%)

I don't have any strong opinion here.

[methane]

Now there is no __init__ call.

[tirkarthi]

This seems like a new property as per current docs at https://docs.python.org/3.8/library/ipaddress.html#ipaddress.IPv4Interface . Should this be documented?

[tirkarthi]

@methane This might increase the scope of the PR but there are functions where int(self) is used that can directly use self._ip for noticeable speed boost in https://bugs.python.org/issue25430#msg331931 in case you want to adopt this in the PR or if it's worthy enough I can make a separate PR. There is a PR for optimizing __contains__ check at #1785 that reduces time by 70% .

Explanation from Serhiy on the optimization : https://bugs.python.org/issue25430#msg294442