[Python-ideas] Give ipaddresses an __index__ method

Steven D'Aprano steve at pearwood.info
Wed Feb 14 19:18:23 EST 2018

This idea is inspired by Eric Osborne's post "Extending __format__ 
method in ipaddress", but I wanted to avoid derailing that thread.

I notice what seems to be an inconsistency in the ipaddress objects:

py> v4 = ipaddress.IPv4Address('')
py> bin(v4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'IPv4Address' object cannot be interpreted as an integer

But that's surely not right: we just need to explicitly do so:

py> bin(int(v4))

IP addresses are, in a strong sense, integers: either 32 or 128 bits. 
And they can be explicitly converted losslessly to and from integers:

py> v4 == ipaddress.IPv4Address(int(v4))

Is there a good reason not to give them an __index__ method so that 
bin(), oct() and hex() will work directly?

py> class X(ipaddress.IPv4Address):
...     def __index__(self):
...             return int(self)
py> a = X('')
py> bin(a)

I acknowledge one potentially undesirable side-effect: this would 
allow using IP addresses as indexes into sequences:

py> 'abcdef'[X('')]

but while it's weird to do this, I don't think it's logically wrong.


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