GH-65056: Improve the IP address' is_global/is_private documentation (GH-113186)

* GH-65056: Improve the IP address' is_global/is_private documentation

It wasn't clear what the semantics of is_global/is_private are and, when
one gets to the bottom of it, it's not quite so simple (hence the
exceptions listed).

Co-authored-by: Petr Viktorin <encukou@gmail.com>

1 files changed, 45 insertions, 13 deletions

diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index e398cc1..7d6edcf 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1333,18 +1333,38 @@ class IPv4Address(_BaseV4, _BaseAddress):
     @property
     @functools.lru_cache()
     def is_private(self):
-        """Test if this address is allocated for private networks.
+        """``True`` if the address is defined as not globally reachable by
+        iana-ipv4-special-registry_ (for IPv4) or iana-ipv6-special-registry_
+        (for IPv6) with the following exceptions:
 
-        Returns:
-            A boolean, True if the address is reserved per
-            iana-ipv4-special-registry.
+        * ``is_private`` is ``False`` for ``100.64.0.0/10``
+        * For IPv4-mapped IPv6-addresses the ``is_private`` value is determined by the
+            semantics of the underlying IPv4 addresses and the following condition holds
+            (see :attr:`IPv6Address.ipv4_mapped`)::
+
+                address.is_private == address.ipv4_mapped.is_private
 
+        ``is_private`` has value opposite to :attr:`is_global`, except for the ``100.64.0.0/10``
+        IPv4 range where they are both ``False``.
         """
         return any(self in net for net in self._constants._private_networks)
 
     @property
     @functools.lru_cache()
     def is_global(self):
+        """``True`` if the address is defined as globally reachable by
+        iana-ipv4-special-registry_ (for IPv4) or iana-ipv6-special-registry_
+        (for IPv6) with the following exception:
+
+        For IPv4-mapped IPv6-addresses the ``is_private`` value is determined by the
+        semantics of the underlying IPv4 addresses and the following condition holds
+        (see :attr:`IPv6Address.ipv4_mapped`)::
+
+            address.is_global == address.ipv4_mapped.is_global
+
+        ``is_global`` has value opposite to :attr:`is_private`, except for the ``100.64.0.0/10``
+        IPv4 range where they are both ``False``.
+        """
         return self not in self._constants._public_network and not self.is_private
 
     @property
@@ -2049,13 +2069,19 @@ class IPv6Address(_BaseV6, _BaseAddress):
     @property
     @functools.lru_cache()
     def is_private(self):
-        """Test if this address is allocated for private networks.
+        """``True`` if the address is defined as not globally reachable by
+        iana-ipv4-special-registry_ (for IPv4) or iana-ipv6-special-registry_
+        (for IPv6) with the following exceptions:
 
-        Returns:
-            A boolean, True if the address is reserved per
-            iana-ipv6-special-registry, or is ipv4_mapped and is
-            reserved in the iana-ipv4-special-registry.
+        * ``is_private`` is ``False`` for ``100.64.0.0/10``
+        * For IPv4-mapped IPv6-addresses the ``is_private`` value is determined by the
+            semantics of the underlying IPv4 addresses and the following condition holds
+            (see :attr:`IPv6Address.ipv4_mapped`)::
+
+                address.is_private == address.ipv4_mapped.is_private
 
+        ``is_private`` has value opposite to :attr:`is_global`, except for the ``100.64.0.0/10``
+        IPv4 range where they are both ``False``.
         """
         ipv4_mapped = self.ipv4_mapped
         if ipv4_mapped is not None:
@@ -2064,12 +2090,18 @@ class IPv6Address(_BaseV6, _BaseAddress):
 
     @property
     def is_global(self):
-        """Test if this address is allocated for public networks.
+        """``True`` if the address is defined as globally reachable by
+        iana-ipv4-special-registry_ (for IPv4) or iana-ipv6-special-registry_
+        (for IPv6) with the following exception:
 
-        Returns:
-            A boolean, true if the address is not reserved per
-            iana-ipv6-special-registry.
+        For IPv4-mapped IPv6-addresses the ``is_private`` value is determined by the
+        semantics of the underlying IPv4 addresses and the following condition holds
+        (see :attr:`IPv6Address.ipv4_mapped`)::
+
+            address.is_global == address.ipv4_mapped.is_global
 
+        ``is_global`` has value opposite to :attr:`is_private`, except for the ``100.64.0.0/10``
+        IPv4 range where they are both ``False``.
         """
         return not self.is_private