Hello up there. I've hit a discrepancy in howz flags is handled by% in unicode and bytes:

• for unicode% rejects it as "unsupported format character" according to original discussion instring formatting: normalize negative zero #90153 (=BPO-45995),
• hower for bytes% fully handles "z":

kirr@deca:~$python3Python 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0] on linuxType "help", "copyright", "credits" or "license" for more information.>>> '%zf' % 1                                       <--   unicodeTraceback (most recent call last):  File "<stdin>", line 1, in <module>ValueError: unsupported format character 'z' (0x7a) at index 1>>> b'%zf' % 1                                      <--   bytesb'1.000000'>>> b'%zf' % 0.0                                    <--   +0 -> 0b'0.000000'>>> b'%zf' % -0.0                                   <--   -0 -> 0b'0.000000'>>> b'%f' % -0.0                                    <--   -0 -> -0 if run without 'z'b'-0.000000'

In other words there is inconsistency in how 'z' is handled by '%' for unicode and bytes, and there is also inconsistency in how 'z' was supposed to be handled by.format and not handled by '%' as originally discussed onBPO-45995.

'z' handling was implemented in#30049 and indeed there I see b'%z' being fully handled:

b0b836b20cb5#diff-f6d440aad34e1c4535c0d898c0197a95490766c745991caace6f64b5dd1ece51

but u'%z' being only partly handled internally without corresponding frontend parsing that bytes has:

b0b836b20cb5#diff-34c966e7876d6f8bf801dd51896327e4f68bba02cddb95fbf3963f0b2e39c38a

In my view the fix should be either a) to add '%z' handling to unicode, or b) to remove '%z' handling from bytes.

Thanks beforehand,
Kirill

• CPython versions tested on: 3.11.2
• Operating system and architecture: Debian GNU/Linux 12 on AMD64

/cc@belm0,@mdickinson

Linked PRs

• gh-104018: disallow "z" format specifier in %-format of byte strings #104033
• [3.11] gh-104018: disallow "z" format specifier in %-format of byte strings (GH-104033) #104058
• gh-104018: remove unused format "z" handling in string formatfloat() #104107
• [3.11] gh-104018: remove unused format "z" handling in string formatfloat() (GH-104107) #104260