Unicode control characters are not allowed as identifiers

[baijum]

BPO	5358
Nosy	@loewis, @ezio-melotti
Files	identifier.py: File with Unicode control character in identifier

^{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 2009-02-27.18:32:17.612>
created_at = <Date 2009-02-24.11:53:50.445>
labels = ['type-bug', 'expert-unicode']
title = 'Unicode control characters are not allowed as identifiers'
updated_at = <Date 2009-02-27.18:32:17.537>
user = 'https://bugs.python.org/baijum'

bugs.python.org fields:

activity = <Date 2009-02-27.18:32:17.537>
actor = 'loewis'
assignee = 'none'
closed = True
closed_date = <Date 2009-02-27.18:32:17.612>
closer = 'loewis'
components = ['Unicode']
creation = <Date 2009-02-24.11:53:50.445>
creator = 'baijum'
dependencies = []
files = ['13162']
hgrepos = []
issue_num = 5358
keywords = []
message_count = 7.0
messages = ['82664', '82666', '82820', '82821', '82822', '82842', '82858']
nosy_count = 4.0
nosy_names = ['loewis', 'ezio.melotti', 'mrabarnett', 'baijum']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue5358'
versions = ['Python 3.0', 'Python 3.1']

[baijum]

I tried to use Zero-width joiner (U+200D) as part of an identifier.
It produce an exception like this:

SyntaxError: invalid character in identifier

I have attached the Python file which produce this error.

Zero-width joiner (U+200D) is a Unicode control character:
http://en.wikipedia.org/wiki/Unicode_control_characters

[loewis]

Why do you think this is a bug?

[baijum]

On a further look at this issue, I understood Python cannot use all
Unicode control characters as identifiers. But for many international
languages, without some control characters like ZWJ & ZWNJ [1], it won't
be possible to construct all characters with proper visual
representation. So, if Python really want to support international
characters as identifiers (for some reason), ZWJ & ZWNJ are unavoidable,
may be some other characters also.

[1] http://en.wikipedia.org/wiki/Zero-width_joiner
http://en.wikipedia.org/wiki/Zero-width_non-joiner

[baijum]

I think RFC-3454 [1] can be used as a base for selecting the control
characters which can be used as a valid identifier character.

[1] http://www.rfc-editor.org/rfc/rfc3454.txt

[ezio-melotti]

Valid identifiers should begin with a letter or '_' and contain only
letters, numbers and '_'. This probably means that only the Unicode
characters that belong to the categories Ll, Lu (Letter Lower/Upper
case), Nd (Number, Decimal Digit) and Pc (Punctuation, Connector) - and
possibly other categories like Lm, Lt, No and Nl - are valid.

Some examples:
>>> ａ－ｂ = 5 # U+FF0D, Cat: Pd, FULLWIDTH HYPHEN-MINUS
SyntaxError: invalid character in identifier
>>> a＃ = 5 # U+FF03, Cat: Po, FULLWIDTH NUMBER SIGN
SyntaxError: invalid character in identifier
>>> a）b = 5 # U+FF09, Cat: Pe, FULLWIDTH RIGHT PARENTHESIS
SyntaxError: invalid character in identifier
>>> ａ＿ｂ = 5 # U+FF3F, Cat: Pc, FULLWIDTH LOW LINE
>>> ａ＿ｂ
5
>>> a﹍b﹎c﹏d = 5 # U+FE4D, U+FE4E, U+FE4F, Cat: Pc
>>> a﹍b﹎c﹏d
5

[mrabarnett]

The definition of a word in the new re module (actually targetted at
Python 2.7) is currently a sequence of L&, N&, M& and Pc.

I suppose ideally we want the definitions of a word and an identifier to
be basically the same, except that an identifier can't start with N&.

[loewis]

See PEP-3131 for a specification what is an identifier in Python.

Closing this as "won't fix".