PEP 461: Inconsistency between str and bytes formatting of integers

[serhiy-storchaka]

BPO	23466
Nosy	@vstinner, @ethanfurman, @serhiy-storchaka, @wm75
Files	bytes_int_format.patch bytes_format_overflow.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-04-03.17:56:55.526>
created_at = <Date 2015-02-15.18:21:46.822>
labels = ['interpreter-core', 'type-bug']
title = 'PEP 461: Inconsistency between str and bytes formatting of integers'
updated_at = <Date 2015-04-04.14:31:51.010>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-04-04.14:31:51.010>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-04-03.17:56:55.526>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2015-02-15.18:21:46.822>
creator = 'serhiy.storchaka'
dependencies = []
files = ['38156', '38812']
hgrepos = []
issue_num = 23466
keywords = ['patch']
message_count = 18.0
messages = ['236056', '236113', '239157', '239191', '239553', '239561', '239569', '239922', '239933', '239941', '239955', '239958', '239962', '240011', '240018', '240070', '240077', '240078']
nosy_count = 5.0
nosy_names = ['vstinner', 'ethan.furman', 'python-dev', 'serhiy.storchaka', 'wolma']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23466'
versions = ['Python 3.5']

[serhiy-storchaka]

PEP-461 says that all numeric bytes formatting codes will work as they do for str. In particular b"%x" % val is equivalent to ("%x" % val).encode("ascii"). But this is wrong with current implementation:

>>> '%x' % 3.14
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: %x format: an integer is required, not float
>>> b'%x' % 3.14
b'3'

The same is for %X, %o and %c.

Raising TypeError on non-integer input to %c, %o, %x, and %X was added in bpo-19995.

[serhiy-storchaka]

Here is a patch.

The difference between string and bytes formatting is that %c with out of the range integer raises OverflowError for str and TypeError for bytes. May be ValueError is more suitable in both cases.

[serhiy-storchaka]

Ethan?

[vstinner]

The patch looks good to me, except of a question added on the review.

[ethanfurman]

Patch looks good.

Changing the raised exceptions to ValueError would require deprecation periods.

[vstinner]

Changing the raised exceptions to ValueError would require deprecation
periods.

bytes%args is not a new feature of python 3.5? It sounds strange to
deprecate a part of a new feature.

[python-dev]

New changeset cb96fd376baa by Serhiy Storchaka in branch 'default':
Issue bpo-23466: %c, %o, %x, and %X in bytes formatting now raise TypeError on
https://hg.python.org/cpython/rev/cb96fd376baa

[ethanfurman]

It's a new feature for 3.5 that is partly responsible for compatibility with 2.7 code.

2.7 raises Overflow error, so 3.5 should also (for out of range values -- wrong value types raise TypeError).

[ethanfurman]

b'%c' is still raising a TypeError. The error message is fine ("%c requires an integer in range(256) or a single byte") but it should be an OverflowError for backwards compatibility.