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))

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #34394344 | 📁 Comparing e9745c3 against main (1860130)

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2 files changed

± whatsnew/3.16.html
± whatsnew/changelog.html

[fedonman]

@StanFromIreland Thanks for the comments! Implemented all.

[StanFromIreland]

Thanks, this looks good to me. @orsenthil can you please take a look as well?

[orsenthil]

While technically this style can be used self.__class__((next_ip, next_prefix)) m because IPv4Network and IPv6Network do the _split_addr_prefix, we do not advertise or mention about this the value of the address argument. This styled tripped me a bit.

I would prefer the previous style.

return self.__class__(
                f"{self._string_from_ip_int(next_ip)}/{next_prefix}"
            )

Because of what we say address can be in the doc strings of the class.

[orsenthil]

I realize that public docs document that.
https://docs.python.org/3/library/ipaddress.html#ipaddress.IPv4Network
https://docs.python.org/3/library/ipaddress.html#ipaddress.IPv6Network

The change might simply be a follow up doc string patch on here.

cpython/Lib/ipaddress.py

Lines 2301 to 2319 in a6d25db

	address: A string or integer representing the IPv6 network or the
	IP and prefix/netmask.
	'2001:db8::/128'
	'2001:db8:0000:0000:0000:0000:0000:0000/128'
	'2001:db8::'
	are all functionally the same in IPv6. That is to say,
	failing to provide a subnetmask will create an object with
	a mask of /128.
	Additionally, an integer can be passed, so
	IPv6Network('2001:db8::') ==
	IPv6Network(42540766411282592856903984951653826560)
	or, more generally
	IPv6Network(int(IPv6Network('2001:db8::'))) ==
	IPv6Network('2001:db8::')
	strict: A boolean. If true, ensure that we have been passed
	A true network address, eg, 2001:db8::1000/124 and not an
	IP address on a network, eg, 2001:db8::1/124.

[orsenthil]

LGTM

[orsenthil]

Thanks for the patch @fedonman and review and ping @StanFromIreland .

[orsenthil]

@StanFromIreland - could you please review this follow up PR #157280