unicode error should raise a value error

[shihai1991]

BPO	37377
Nosy	@stevendaprano, @shihai1991

^{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 = None
closed_at = <Date 2019-06-23.14:15:14.926>
created_at = <Date 2019-06-23.13:29:20.802>
labels = ['interpreter-core', 'type-bug', '3.9']
title = 'unicode error should raise a value error'
updated_at = <Date 2019-06-23.14:15:14.925>
user = 'https://github.com/shihai1991'

bugs.python.org fields:

activity = <Date 2019-06-23.14:15:14.925>
actor = 'shihai1991'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-23.14:15:14.926>
closer = 'shihai1991'
components = ['Interpreter Core']
creation = <Date 2019-06-23.13:29:20.802>
creator = 'shihai1991'
dependencies = []
files = []
hgrepos = []
issue_num = 37377
keywords = []
message_count = 3.0
messages = ['346321', '346324', '346326']
nosy_count = 2.0
nosy_names = ['steven.daprano', 'shihai1991']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37377'
versions = ['Python 3.9']

[shihai1991]

>>> "\x1"
  File "<stdin>", line 1
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-2: truncated \xXX escape

I think rasing the valueError would be exact.(PEP-223 agree this behavior: https://www.python.org/dev/peps/pep-0223/#bdfl-pronouncements).

And I think the error type could be changed in:
https://github.com/python/cpython/blob/master/Python/ast.c#L682

[stevendaprano]

It is a *syntax* error. You have written bad syntax, just as the error message says. Your \xXX code is too short, only 1 hex digit instead of 2. I disagree that this should be a value error: it isn't a bad value, it is bad syntax.

I don't know what the context of the BDFL pronouncement in PEP-223 was, but I think it was decided later that Guido wrong because the error in Python 2.4 and 2.5 was UnicodeDecodeError and then changed to SyntaxError in 2.6 (probably to match Python 3, I guess).

In Python 3, both unicode and bytes strings give a syntax error for this error.

[shihai1991]

Got it, thank for your detailed explanation, steven.