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Merged
serhiy-storchaka merged 9 commits into from
May 5, 2026
Merged

gh-139489: Add xml.is_valid_name() #139768

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c7cbb61
gh-139489: Add xml.sax.utils.is_valid_name()
serhiy-storchaka Oct 8, 2025
4f37eed
Fix references.
serhiy-storchaka Oct 8, 2025
6ac604e
dd
serhiy-storchaka Apr 30, 2026
e814cfa
Move to the toplevel xml module.
serhiy-storchaka Apr 30, 2026
bc26874
Use possesive quantifier for optimization.
serhiy-storchaka Apr 30, 2026
b631754
Merge branch 'main' into xml-sax-utils-is_valid_name
serhiy-storchaka May 1, 2026
8db41b9
Merge branch 'main' into xml-sax-utils-is_valid_name
serhiy-storchaka May 2, 2026
7e96492
Apply suggestions from code review
serhiy-storchaka May 2, 2026
3245a65
Import re as _re.
serhiy-storchaka May 4, 2026
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15 changes: 15 additions & 0 deletions Doc/library/xml.rst
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Expand Up@@ -41,6 +41,21 @@ The XML handling submodules are:
* :mod:`xml.sax`: SAX2 base classes and convenience functions
* :mod:`xml.parsers.expat`: the Expat parser binding

This module also defines utility functions.

.. function:: is_valid_name(name)

Return ``True`` if the string is a valid element or attribute name,
``False`` otherwise.

Almost all characters are permitted in names, except control characters and
those which either are or reasonably could be used as delimiters.

@picnixzpicnixzMay 2, 2026

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Maybe add a link to the specs if any?

@vstinnervstinnerMay 2, 2026

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Link found in the implementation: https://www.w3.org/TR/xml/#NT-Name.

@picnixzpicnixzMay 2, 2026

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I think it would be good to add it in the online docs as well. It'll be more accessible.

@serhiy-storchakaserhiy-storchakaMay 2, 2026

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I am going to add several more functions. Some functions will need several links, and some links will be repeated for different functions. If we want to add links, it is better to add root links to the XML specifications at the top of the module documentation.

@picnixzpicnixzMay 2, 2026

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That's also ok. As long as the online docs contain some links to some specifications, it's ok.

Characters like ":", "-", ".", "_", and "·" are permitted, but "<", "/",
"!", "?", and "=" are forbidden.
The name cannot start with a digit or a character like "-", ".", and "·".

..versionadded:: next


.. _xml-security:
.. _xml-vulnerabilities:
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8 changes: 8 additions & 0 deletions Doc/whatsnew/3.15.rst
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Expand Up@@ -1530,6 +1530,14 @@ wave
(Contributed by Lionel Koenig and Michiel W. Beijen in :gh:`60729`.)


xml
---

* Add the :func:`xml.is_valid_name` function, which allows to check
whether a string can be used as an element or attribute name in XML.
(Contributed by Serhiy Storchaka in :gh:`139489`.)


xml.parsers.expat
-----------------

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27 changes: 27 additions & 0 deletions Lib/test/test_xml.py
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@@ -0,0 +1,27 @@
import xml
import unittest


class TestUtils(unittest.TestCase):

def test_is_valid_name(self):
is_valid_name = xml.is_valid_name
self.assertFalse(is_valid_name(''))
self.assertTrue(is_valid_name('name'))
self.assertTrue(is_valid_name('NAME'))
self.assertTrue(is_valid_name('name0:-._·'))
self.assertTrue(is_valid_name('_'))
self.assertTrue(is_valid_name(':'))
self.assertTrue(is_valid_name('Ñàḿĕ'))
self.assertTrue(is_valid_name('\U000EFFFF'))
self.assertFalse(is_valid_name('0'))
self.assertFalse(is_valid_name('-'))
self.assertFalse(is_valid_name('.'))
self.assertFalse(is_valid_name('·'))
self.assertFalse(is_valid_name('na me'))
for c in '<>/!?=\x00\x01\x7f\ud800\udfff\ufffe\uffff\U000F0000':
self.assertFalse(is_valid_name('name' + c))


if __name__ == '__main__':
unittest.main()
3 changes: 2 additions & 1 deletion Lib/xml/__init__.py
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Expand Up@@ -16,5 +16,6 @@

"""

from .utils import *

__all__ = ["dom", "parsers", "sax", "etree"]
__all__ = ["dom", "parsers", "sax", "etree", "is_valid_name"]
25 changes: 25 additions & 0 deletions Lib/xml/utils.py
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@@ -0,0 +1,25 @@
lazy import re as _re


@picnixzpicnixzMay 2, 2026

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I'd suggest adding an __all__

@vstinnervstinnerMay 2, 2026

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It's needed. Currently, the re module is exposed as a xml attribute:

$ ./python
>>> import xml
>>> xml.re
<module 're' from '/home/vstinner/python/main/Lib/re/__init__.py'>

def is_valid_name(name):
"""Test whether a string is a valid element or attribute name."""
# https://www.w3.org/TR/xml/#NT-Name
return _re.fullmatch(
# NameStartChar
'['
':A-Z_a-z'
'\xC0-\xD6\xD8-\xF6\xF8-\u02FF\u0370-\u037D\u037F-\u1FFF'
'\u200C\u200D'
'\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF'
'\uF900-\uFDCF\uFDF0-\uFFFD\U00010000-\U000EFFFF'
']'
# NameChar
'['
r'\-.0-9:A-Z_a-z'
'\xB7'
'\xC0-\xD6\xD8-\xF6\xF8-\u037D\u037F-\u1FFF'
'\u200C\u200D\u203F\u2040'
'\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF'
'\uF900-\uFDCF\uFDF0-\uFFFD\U00010000-\U000EFFFF'
']*+',
name) is not None
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-10-08-15-36-00.gh-issue-139489.W46tvn.rst
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@@ -0,0 +1,2 @@
Add the :func:`xml.is_valid_name` function, which allows to check
whether a string can be used as an element or attribute name in XML.
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