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bpo-14465: Add an indent() function to xml.etree.ElementTree to pretty-print XML trees.
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‎Doc/library/xml.etree.elementtree.rst

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@@ -572,6 +572,18 @@ Functions
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.. versionadded:: 3.2
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.. function:: indent(tree, space=" ", level=0)
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Appends whitespace to the subtree to indent the tree visually.
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This can be used to generate pretty-printed XML output.
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*tree* can be an Element or ElementTree. *space* is the whitespace
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string that will be inserted for each indentation level, two space
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characters by default. For indenting partial subtrees inside of an
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already indented tree, pass the initial indentation level as *level*.
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.. versionadded:: 3.9
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.. function:: iselement(element)
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Checks if an object appears to be a valid element object. *element* is an

‎Lib/test/test_xml_etree.py

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@@ -788,6 +788,74 @@ def test_writestring(self):
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elem = ET.fromstring("<html><body>text</body></html>")
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self.assertEqual(ET.tostring(elem), b'<html><body>text</body></html>')
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def test_indent(self):
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elem = ET.XML("<root></root>")
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ET.indent(elem)
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self.assertEqual(ET.tostring(elem), b'<root />')
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elem = ET.XML("<html><body>text</body></html>")
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ET.indent(elem)
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self.assertEqual(ET.tostring(elem), b'<html>\n <body>text</body>\n</html>')
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elem = ET.XML("<html><body>text</body>tail</html>")
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ET.indent(elem)
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self.assertEqual(ET.tostring(elem), b'<html>\n <body>text</body>tail</html>')
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elem = ET.XML("<html><body><p>par</p><p>text</p><p><br/></p></body></html>")
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ET.indent(elem)
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self.assertEqual(
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ET.tostring(elem),
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b'<html>\n'
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b' <body>\n'
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b' <p>par</p>\n'
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b' <p>text</p>\n'
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b' <p>\n'
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b' <br />\n'
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b' </p>\n'
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b' </body>\n'
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b'</html>'
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)
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elem = ET.XML("<html><body><p>pre<br/>post</p><p>text</p></body></html>")
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ET.indent(elem)
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self.assertEqual(
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ET.tostring(elem),
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b'<html>\n'
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b' <body>\n'
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b' <p>pre<br />post</p>\n'
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b' <p>text</p>\n'
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b' </body>\n'
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b'</html>'
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)
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elem = ET.XML("<html><body><p>pre<br/>post</p><p>text</p></body></html>")
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ET.indent(elem, space='\t')
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self.assertEqual(
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ET.tostring(elem),
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b'<html>\n'
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b'\t<body>\n'
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b'\t\t<p>pre<br />post</p>\n'
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b'\t\t<p>text</p>\n'
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b'\t</body>\n'
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b'</html>'
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)
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def test_indent_space_caching(self):
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elem = ET.XML("<html><body><p>par</p><p>text</p><p><br/></p><p /></body></html>")
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ET.indent(elem)
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self.assertEqual(
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{el.tail for el in elem.iter()},
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{None, "\n", "\n ", "\n "}
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)
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self.assertEqual(
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{el.text for el in elem.iter()},
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{None, "\n ", "\n ", "\n ", "par", "text"}
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)
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self.assertEqual(
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len({el.tail for el in elem.iter()}),
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len({id(el.tail) for el in elem.iter()}),
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)
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def test_tostring_default_namespace(self):
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elem = ET.XML('<body xmlns="http://effbot.org/ns"><tag/></body>')
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self.assertEqual(

‎Lib/xml/etree/ElementTree.py

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@@ -76,7 +76,7 @@
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"dump",
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"Element", "ElementTree",
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"fromstring", "fromstringlist",
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"iselement", "iterparse",
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"indent", "iselement", "iterparse",
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"parse", "ParseError",
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"PI", "ProcessingInstruction",
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"QName",
@@ -1185,6 +1185,55 @@ def dump(elem):
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if not tail or tail[-1] != "\n":
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sys.stdout.write("\n")
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def indent(tree, space=" ", level=0):
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"""Indent an XML document by inserting newlines and indentation space
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after elements.
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*tree* is the ElementTree or Element to modify. The (root) element
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itself will not be changed, but the tail text of all elements in its
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subtree will be adapted.
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*space* is the whitespace to insert for each indentation level, two
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space characters by default.
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*level* is the initial indentation level. Setting this to a higher
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value than 0 can be used for indenting subtrees that are more deeply
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nested inside of a document.
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"""
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if isinstance(tree, ElementTree):
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tree = tree.getroot()
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if not len(tree):
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return
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# Reduce the memory consumption by reusing indentation strings.
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class _indentation_cache(dict):
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def __missing__(self, level):
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s = self[level] = "\n" + level * space
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return s
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indentations = _indentation_cache()
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def _indent_children(elem, level):
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# Start a new indentation level for the first child.
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child_level = level + 1
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child_indentation = indentations[child_level]
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if not elem.text or not elem.text.strip():
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elem.text = child_indentation
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for child in elem:
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if len(child):
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_indent_children(child, child_level)
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if not child.tail or not child.tail.strip():
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child.tail = child_indentation
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# Dedent after the last child.
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if not child.tail or not child.tail.strip():
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child.tail = indentations[level]
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_indent_children(tree, level)
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# --------------------------------------------------------------------
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# parsing
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‎Misc/NEWS.d/next/Library/2019-08-10-18-50-04.bpo-14465.qZGC4g.rst

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Add an xml.etree.ElementTree.indent() function for pretty-printing XML trees.
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Contributed by Stefan Behnel.

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