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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
84b22d4
Make iselement stricter + incorporate feedback
abstractedfox Jun 22, 2025
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36 changes: 36 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 @@ -218,6 +218,42 @@ class ElementTreeTest(unittest.TestCase):
def serialize_check(self, elem, expected):
self.assertEqual(serialize(elem), expected)

def test_constructor(self):
# Test constructor behavior.

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

# Test _setroot as well, since it also sets the _root object.

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

# Make sure it accepts an Element-like object.

class ElementLike:
def __init__(self):
self.tag = "tag"
self.text = None
self.tail = None
def iter(self):
pass
def items(self):
pass
def __len__(self):
pass

element_like = ElementLike()
try:
tree = ET.ElementTree(element_like)
except Exception as err:
self.fail(err)
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Maybe test also _setroot() here?


def test_interface(self):
# Test element tree interface.

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13 changes: 9 additions & 4 deletions Lib/xml/etree/ElementTree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -120,8 +120,9 @@ class ParseError(SyntaxError):

def iselement(element):
"""Return True if *element* appears to be an Element."""
return hasattr(element, 'tag')

return (hasattr(element, 'tag') and hasattr(element, 'text') and
hasattr(element, 'tail') and callable(element.iter) and
callable(element.items) and callable(element.__len__))
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Does this function raise an exception if iter(), items() or __len__() method doesn't exist?


class Element:
"""An XML element.
Expand Down Expand Up @@ -527,7 +528,9 @@ 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 xml.etree.Element, "
f"not {type(element).__name__}")
self._root = element # first node
if file:
self.parse(file)
Expand All @@ -543,7 +546,9 @@ def _setroot(self, element):
with the given element. Use with care!

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

def parse(self, source, parser=None):
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-06-22-02-16-17.gh-issue-135640.FXyFL6.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Address bug where calling :func:`xml.etree.ElementTree.ElementTree.write` on
an ElementTree object with an invalid root element would blank the file
passed to ``write`` if it already existed.
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