gh-156680: Raise the documented error from IPv6Network.next_network()

[fedonman]

Range-check next_ip against _ALL_ONES in next_network() instead of catching OverflowError, which only the IPv4 path raises. The IPv6 path went through _BaseV6._string_from_ip_int(), whose ValueError escaped uncaught.

next_network() is new in 3.16 and unreleased, so this is folded into the entry the method landed with and needs no NEWS fragment.

testNextNetworkOutOfAddressSpace (test.test_ipaddress.IpaddrUnitTest.testNextNetworkOutOfAddressSpace) ... ok
Total tests: run=1 (filtered)
Result: SUCCESS
Total tests: run=215
Result: SUCCESS

• Issue: IPv6Network.next_network() raises the wrong error when addresses run out #156680

[StanFromIreland]

Thanks! Can you also please fix the What's New entry (and news entry) for these:

[StanFromIreland]

Also, reviewing fadb785 please fix the docstring of next_network, the sentence detailing the arguments is missing a period and there's no raises section.

[StanFromIreland]

Oh and one more thing. I don't quite understand why we're doing this little dance with _string_from_ip_int, when we can create an instance directly.

Apologies for all the changes I've asked you to make, indeed it grew to be quite a long list. As such, here's a patch instead:

--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1124,11 +1124,15 @@ def next_network(self, next_prefix=None):
 
         Args:
             next_prefix: The desired next prefix length, if not specified the
-            same self.prefixlen will be used
+            same self.prefixlen will be used.
 
         Returns:
             An IPv(4|6) Network object of the next closest network.
 
+        Raises:
+            ValueError: If next_prefix is outside the range of valid prefix
+            lengths, or if no further network of that size exists.
+
         """
         if next_prefix is None:
             next_prefix = self.prefixlen
@@ -1150,15 +1154,13 @@ def next_network(self, next_prefix=None):
             ((new_netmask._ip & self.network_address._ip) >> bit_shift) + 1
         ) << bit_shift
 
-        try:
-            return self.__class__(
-                f"{self._string_from_ip_int(next_ip)}/{next_prefix}"
-            )
-        except OverflowError:
+        if next_ip > self._ALL_ONES:
             raise ValueError(
                 f"out of address space, cannot make another /{next_prefix} "
                 "network"
-            ) from None
+            )
+
+        return self.__class__((next_ip, next_prefix))