[issue32820] Add bits method to ipaddress

[Nick Coghlan]

Nick Coghlan <ncoghlan at gmail.com> added the comment:

I think the aspect that makes this potentially worthy of a helper function is the need to dynamically adjust the field width based on whether you're printing an IPv4 address or an IPv6 one, whether you're printing it in binary or hexadecimal, whether you're printing separator characters, and whether you're printing the base indicator prefix.

For example, consider the following:

```
>>> ip4 = ipaddress.ip_address("1.2.3.4")
>>> ip4
IPv4Address('1.2.3.4')
>>> ip6 = ipaddress.ip_address("::1:2:3:4")
>>> ip6
IPv6Address('::1:2:3:4')
>>> format(int(ip4), "#041_b")
'0b0000_0001_0000_0010_0000_0011_0000_0100'
>>> format(int(ip6), "#041_x")
'0x0000_0000_0000_0000_0001_0002_0003_0004'
```

The "41" in those examples comes from "prefix_len + (num_bits / bits_per_char) + (num_bits / bits_per_char / chars_per_separator) - 1":

IPv4 in binary: 2 + (32 / 1) + (32 / 1 / 4) - 1 = 2 + 32 + 8 - 1 = 41
IPv6 in hex: 2 + (128 / 4) + (128 / 1 / 4) - 1 = 2 + 32 + 8 - 1 = 41

So I think the potentially interesting method to implement here would be *__format__*, such that the field width calculation could be made implicit based on the other options selected.

While backwards compatibility means that IP address formatting would still need to be equivalent to "str(ip)" by default, it would be reasonably straightforward to make "format(ip, 'b')" output the number in binary, "format(ip, 'x')" do it in hex, and "format(ip, 'n')" be equivalent to "b" for IPv4 addresses, and "x" for IPv6 ones.

Unlike ordinary numbers, the IP addresses would always be zero-padded to a fixed width (32-bits for IPv4, 128 bits for IPv6), but "#" and "_" would be accepted to indicate whether or to add the base indicator prefix and/or group separators.

Given those enhancements, the display examples above would become:

```
>>> format(ip4, "#_n")
'0b0000_0001_0000_0010_0000_0011_0000_0100'
>>> format(ip6, "#_n")
'0x0000_0000_0000_0000_0001_0002_0003_0004'
```

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32820>
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