bpo-46415: Use f-string for ValueError in ipaddress.ip_{address,network,interface} helper functions

[thomascellerier]

IPv*Network and IPv*Interface constructors accept a 2-tuple of (address description, netmask) as the address parameter.
When the tuple-based address is used errors are not propagated correctly through the ipaddress.ip_* helper because of the %-formatting now expecting several arguments:

In [7]: ipaddress.ip_network(("192.168.100.0", "fooo"))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-7-7fc0bff07012> in <module>
----> 1 ipaddress.ip_network(("192.168.100.0", "fooo"))

/usr/lib/python3.8/ipaddress.py in ip_network(address, strict)
     81         pass
     82
---> 83     raise ValueError('%r does not appear to be an IPv4 or IPv6 network' %
     84                      address)
     85

TypeError: not all arguments converted during string formatting

Compared to:

In [8]: ipaddress.IPv4Network(("192.168.100.0", "foo"))
---------------------------------------------------------------------------
NetmaskValueError                         Traceback (most recent call last)
<ipython-input-8-79078758e653> in <module>
----> 1 ipaddress.IPv4Network(("192.168.100.0", "foo"))

/usr/lib/python3.8/ipaddress.py in __init__(self, address, strict)
   1453
   1454         self.network_address = IPv4Address(addr)
-> 1455         self.netmask, self._prefixlen = self._make_netmask(mask)
   1456         packed = int(self.network_address)
   1457         if packed & int(self.netmask) != packed:

/usr/lib/python3.8/ipaddress.py in _make_netmask(cls, arg)
   1118                     # Check for a netmask or hostmask in dotted-quad form.
   1119                     # This may raise NetmaskValueError.
-> 1120                     prefixlen = cls._prefix_from_ip_string(arg)
   1121             netmask = IPv4Address(cls._ip_int_from_prefix(prefixlen))
   1122             cls._netmask_cache[arg] = netmask, prefixlen

/usr/lib/python3.8/ipaddress.py in _prefix_from_ip_string(cls, ip_str)
    516             ip_int = cls._ip_int_from_string(ip_str)
    517         except AddressValueError:
--> 518             cls._report_invalid_netmask(ip_str)
    519
    520         # Try matching a netmask (this would be /1*0*/ as a bitwise regexp).

/usr/lib/python3.8/ipaddress.py in _report_invalid_netmask(cls, netmask_str)
    472     def _report_invalid_netmask(cls, netmask_str):
    473         msg = '%r is not a valid netmask' % netmask_str
--> 474         raise NetmaskValueError(msg) from None
    475
    476     @classmethod

NetmaskValueError: 'foo' is not a valid netmask

Use an f-string to make sure the error is always properly formatted.

https://bugs.python.org/issue46415

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[JelleZijlstra]

Good catch, thanks! This is a classic bug with % formatting.

There are a lot of other instances of % formatting in this file. Most are safe, because they explicitly pass tuples or first check that the argument is some non-tuple type, but I found two others that should probably be fixed:

>>> ipaddress.IPv4Address(("x/", "y"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/jelle/py/cpython/Lib/ipaddress.py", line 1307, in __init__
    raise AddressValueError("Unexpected '/' in %r" % address)
                            ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
TypeError: not all arguments converted during string formatting
>>> ipaddress.IPv6Address(("x/", "y"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/jelle/py/cpython/Lib/ipaddress.py", line 1916, in __init__
    raise AddressValueError("Unexpected '/' in %r" % address)
                            ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
TypeError: not all arguments converted during string formatting

[thomascellerier]

Ah indeed!

I pushed a fix for those 2 and one additional case I found while going through the module.

[JelleZijlstra]

I just found #30087 which fixes the same thing (though not the additional cases we found here, and without tests).

[thomascellerier]

Hmm OK I see. Should I close this PR? Add more tests for the other cases?

[JelleZijlstra]

That's up to the core dev doing the merge I suppose. I'd leave this open until a core dev comes along with a decision.

[hugovk]

That's up to the core dev doing the merge I suppose. I'd leave this open until a core dev comes along with a decision.

@JelleZijlstra you're a core dev now, would you like to come along with a decision? :)

[ghost]

All commit authors signed the Contributor License Agreement.

[JelleZijlstra]

I'd like to merge this one, but @thomascellerier will have to resign the CLA with the new process, sorry for the delay!

[thomascellerier]

Done!

[miss-islington]

Thanks @thomascellerier for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

[bedevere-bot]

GH-92225 is a backport of this pull request to the 3.10 branch.

[bedevere-bot]

GH-92226 is a backport of this pull request to the 3.9 branch.

[JelleZijlstra]

I wasn't sure about whether to backport this, but I think the old behavior is buggy and worth fixing in the other branches. On the other hand, we do change the exception class raised, which could break users' code.