simplify overlaps function in ipaddress.py

[3a37abd6-e522-4049-958c-60aefc9639d0]

BPO	38335
Nosy	@serhiy-storchaka, @s-sanjay
PRs	python/cpython#16519
Files	skip_broadcast_in.patch

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GitHub fields: ```python assignee = None closed_at = None created_at = labels = ['3.8', '3.7', 'library', '3.9'] title = 'simplify overlaps function in ipaddress.py' updated_at = user = 'https://github.com/s-sanjay' ``` bugs.python.org fields: ```python activity = actor = 'Sanjay' assignee = 'none' closed = False closed_date = None closer = None components = ['Library (Lib)'] creation = creator = 'Sanjay' dependencies = [] files = ['48634'] hgrepos = [] issue_num = 38335 keywords = ['patch'] message_count = 3.0 messages = ['353676', '354004', '354005'] nosy_count = 2.0 nosy_names = ['serhiy.storchaka', 'Sanjay'] pr_nums = ['16519'] priority = 'normal' resolution = None stage = 'patch review' status = 'open' superseder = None type = None url = 'https://bugs.python.org/issue38335' versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9'] ```

[3a37abd6-e522-4049-958c-60aefc9639d0]

the current implementation of overlaps function tests either network or broadcast address is in other but we can skip checking broadcast address is in other because we anyway check if other.network_address in self

without loss of generality if we assume self has smaller prefixlen than other then when self.broadcast_address in other then other.network_address *SHOULD* be in self but the reverse is not true

so my first patch was to make the function logic simply do self.network_address in other or other.network_address in self

but the current PR does a different change. We have introduced two new functions subnet_of and supernet_of

for two networks A, B there are only three possibilities

1. they don't overlap
2. A is subnet of B
3. B is subnet of A

so we can reuse the existing function and just do return self.subnet_of(other) or self.supernet_of(other) the only thing is while overlaps() function returns false when we try to compare with a network or with diff version the other throws exception so I added a typecheck in the beginning.

P.S the docstring is slightly convoluted for newcomers, based on the three possibilities it should say "Tell if self is supernet or subnet of other" because "partly contained" can also mean two ranges intersect which can never happen to network prefixes. I have not made that change but can make it.

There are also some other issues I want to address but I want to do one at a time.

[serhiy-storchaka]

What is the benefit of your version?

[3a37abd6-e522-4049-958c-60aefc9639d0]

the version in the patch is less code a or b or c or d becomes a or d

the version in PR is using the subnet_of, supernet_of function because overlap means either a is subnet_of or supernet_of b. So was trying to consolidate the implementation of overlap from 2 to 1.