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gh-135640: Adds type checking to ElementTree.ElementTree constructor #135643

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gh-135640: Adds type checking to ElementTree.ElementTree constructor #135643

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b0a8a64
Tenuous first fix
abstractedfox Jun 17, 2025
f0356c8
Remove commented assertions
abstractedfox Jun 17, 2025
06eaff5
Add tests for ElementTree constructor
abstractedfox Jun 17, 2025
6d4d65f
Add appropriate text to an exception
abstractedfox Jun 17, 2025
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7 changes: 7 additions & 0 deletions Lib/test/test_xml_etree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -247,6 +247,13 @@ def check_element(element):
self.assertRegex(repr(element), r"^<Element 't\xe4g' at 0x.*>$")
element = ET.Element("tag", key="value")

# Verify type checking for ElementTree constructor
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Can you make a separate test method, say "test_constructor" and put that test before test_interface? TiA


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Add also a test where only an Element-like class is tested (only with a tag attribute, nothing else, not even inheriting from xml.etree.Element).

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Hmm, I tried this in a boilerplate file:

class element impl:
    def __init__(self, tag):
        self.tag = tag

..but an instance of that wasn't enough to be able to pass as a root element to an ElementTree instance, call write, and have it work as normal (assuming I understood you properly). I ended up needing to add iter(), items(), __len__(), text, and tail before it would. Was that what you meant?

As a side thought, if ElementTree supports custom element implementations, should I remove the type check and change iselement to check for all of those attributes instead?

with self.assertRaises(TypeError):
tree = ET.ElementTree("")
with self.assertRaises(TypeError):
tree = ET.ElementTree(ET.ElementTree())

# Make sure all standard element methods exist.

def check_method(method):
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8 changes: 6 additions & 2 deletions Lib/xml/etree/ElementTree.py
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Expand Up @@ -527,7 +527,9 @@ class ElementTree:

"""
def __init__(self, element=None, file=None):
# assert element is None or iselement(element)
if element is not None and not iselement(element):
raise TypeError(f"element must be etree.Element, "
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I would appreciate either writing xml.etree.Element or Element only.

I also suspect that the isinstance() check was removed so that elements not inheriting from xml.Element still work, or elements that implement the XML interface without directly inheriting from it.

And the minimal element interface is "tag".

f"not {type(element).__name__}")
self._root = element # first node
if file:
self.parse(file)
Expand All @@ -543,7 +545,9 @@ def _setroot(self, element):
with the given element. Use with care!

"""
# assert iselement(element)
if not iselement(element):
raise TypeError(f"element must be etree.Element, "
f"not {type(element).__name__}")
self._root = element

def parse(self, source, parser=None):
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