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bpo-34160: explain how to deal with attribute order in ElementTree (GH-14867)

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* 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.
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Stefan Behnel 2019-07-24 20:22:50 +02:00 • committed by GitHub
parent c6cb4cdd21
commit a3697db010
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42
Doc/library/xml.etree.elementtree.rst
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@ -659,7 +659,7 @@ Functions
.. 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 @@ Functions
.. 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 @@ Functions
.. 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 @@ Element Objects
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: