Lib/ipaddress.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/ipaddress.py ↗

ipaddress (PEP 3144) provides immutable types for IPv4 and IPv6 addresses, networks, and interfaces. All parsing is pure Python with no C extension.

Map

Lines	Symbol	Role
1-100	ip_address, ip_network, ip_interface	Factory functions; auto-detect v4/v6
101-400	_BaseAddress, _BaseNetwork	Shared base classes; comparison, __contains__
401-750	IPv4Address	32-bit packed int; packed, exploded, is_private, is_loopback
751-1000	IPv4Network	CIDR network; network_address, broadcast_address, hosts(), subnets()
1001-1300	IPv4Interface	Address + network; ip, network, with_prefixlen
1301-1700	IPv6Address	128-bit packed int; ipv4_mapped, sixtofour, teredo, is_link_local
1701-2100	IPv6Network	IPv6 CIDR; subnets(), supernet(), subnet_of()
2101-2300	IPv6Interface, _get_mixed_type_key, collapse_addresses, summarize_address_range	Utilities

Reading

Address storage

Both IPv4Address and IPv6Address store the address as a Python int in self._ip. String parsing converts to the packed int representation.

# CPython: Lib/ipaddress.py:1158 IPv4Address.__init__
def __init__(self, address):
    if isinstance(address, int):
        self._check_int(address, 32)
        self._ip = address
    elif isinstance(address, bytes):
        ...
        self._ip = int.from_bytes(address, 'big')
    else:
        addr_str = str(address)
        ...
        self._ip = struct.unpack('!I', socket.inet_aton(addr_str))[0]

Network operations

IPv4Network stores the network address and prefix length. __contains__ checks if an address falls within the network using bitmask arithmetic.

# CPython: Lib/ipaddress.py:1430 IPv4Network.__contains__
def __contains__(self, other):
    ...
    return (int(other) & int(self.netmask)) == int(self.network_address)

hosts() generator

# CPython: Lib/ipaddress.py:1500 IPv4Network.hosts
def hosts(self):
    network = int(self.network_address)
    broadcast = int(self.broadcast_address)
    for x in range(network + 1, broadcast):
        yield self._address_class(x)

For a /32 it yields the single host address; for a /31 (point-to-point) it yields both addresses.

collapse_addresses

Merges a list of networks into the minimal set of non-overlapping CIDR blocks, using a sorted merge of adjacent prefixes.

gopy notes

Status: not yet ported. Pure Python, no C dependencies. The Go standard library net/netip (Go 1.18+) provides Addr, Prefix, and AddrRange with similar semantics. A gopy port would wrap net/netip types as Python-visible objects.