[3.8] bpo-34160: explain how to deal with attribute order in ElementTree (GH-14867) (GH-14935)
* Fix the formatting in the documentation of the tostring() functions.
* bpo-34160: Document that the tostring() and tostringlist() functions also preserve the attribute order now.
* bpo-34160: Add an explanation of how users should deal with the attribute order.
(cherry picked from commit a3697db0102b9b6747fe36009e42f9b08f0c1ea8)
Co-authored-by: Stefan Behnel <stefan_ml@behnel.de>
diff --git a/Doc/library/xml.etree.elementtree.rst b/Doc/library/xml.etree.elementtree.rst
index c466731..9f46755 100644
--- a/Doc/library/xml.etree.elementtree.rst
+++ b/Doc/library/xml.etree.elementtree.rst
@@ -659,7 +659,7 @@
.. function:: tostring(element, encoding="us-ascii", method="xml", *, \
- xml_declaration=None, default_namespace=None,
+ xml_declaration=None, default_namespace=None, \
short_empty_elements=True)
Generates a string representation of an XML element, including all
@@ -677,9 +677,13 @@
.. versionadded:: 3.8
The *xml_declaration* and *default_namespace* parameters.
+ .. versionchanged:: 3.8
+ The :func:`tostring` function now preserves the attribute order
+ specified by the user.
+
.. function:: tostringlist(element, encoding="us-ascii", method="xml", *, \
- xml_declaration=None, default_namespace=None,
+ xml_declaration=None, default_namespace=None, \
short_empty_elements=True)
Generates a string representation of an XML element, including all
@@ -700,6 +704,10 @@
.. versionadded:: 3.8
The *xml_declaration* and *default_namespace* parameters.
+ .. versionchanged:: 3.8
+ The :func:`tostringlist` function now preserves the attribute order
+ specified by the user.
+
.. function:: XML(text, parser=None)
@@ -930,6 +938,36 @@
if element is None:
print("element not found")
+ Prior to Python 3.8, the serialisation order of the XML attributes of
+ elements was artificially made predictable by sorting the attributes by
+ their name. Based on the now guaranteed ordering of dicts, this arbitrary
+ reordering was removed in Python 3.8 to preserve the order in which
+ attributes were originally parsed or created by user code.
+
+ In general, user code should try not to depend on a specific ordering of
+ attributes, given that the `XML Information Set
+ <https://www.w3.org/TR/xml-infoset/>`_ explicitly excludes the attribute
+ order from conveying information. Code should be prepared to deal with
+ any ordering on input. In cases where deterministic XML output is required,
+ e.g. for cryptographic signing or test data sets, canonical serialisation
+ is available with the :func:`canonicalize` function.
+
+ In cases where canonical output is not applicable but a specific attribute
+ order is still desirable on output, code should aim for creating the
+ attributes directly in the desired order, to avoid perceptual mismatches
+ for readers of the code. In cases where this is difficult to achieve, a
+ recipe like the following can be applied prior to serialisation to enforce
+ an order independently from the Element creation::
+
+ def reorder_attributes(root):
+ for el in root.iter():
+ attrib = el.attrib
+ if len(attrib) > 1:
+ # adjust attribute order, e.g. by sorting
+ attribs = sorted(attrib.items())
+ attrib.clear()
+ attrib.update(attribs)
+
.. _elementtree-elementtree-objects: