ElementTree parsing for non-prefixed attributes with default namespace

et_patch.py

#!/usr/bin/python

from xml.etree import ElementTree as ET
from cStringIO import StringIO

def parse_attrns(file):
    """Parse file to ElementTree instance. Patch non-prefixed attributes
    with the namespace of the element they belong to.
    """
    events = ("start", )
    root = None
    for event, elem in ET.iterparse(file, events):
        if event == "start":
            if root is None:
                root = elem
            if elem.tag.find("}") < 0:
                continue
            # inherit the uri from the element
            uri, _ = elem.tag[1:].rsplit("}", 1)
            for k, v in elem.attrib.items():
                if k[:1] != "{":
                    # replace the old attribute with a namespace-prefixed one
                    del elem.attrib[k]
                    k = "{%s}%s" % (uri, k)
                    elem.attrib[k] = v
    return ET.ElementTree(root)

class fileobj(object):
    def __init__(self, l):
        self.write = l.append

def roundtrip(xml, dns=None):
    """Deserialize XML using ElementTree, then serialize it again.

    >>> roundtrip('<a xmlns="foo"><b id="1" /></a>', dns='foo')
    '<a xmlns="foo"><b id="1" /></a>'

    >>> roundtrip('<a><b id="1" /></a>', dns='foo')
    Traceback (most recent call last):
        ...
    ValueError: cannot use non-qualified names with default_namespace option

    >>> roundtrip('<a><b id="1" /></a>')
    '<a><b id="1" /></a>'

    """
    #e = ET.parse(StringIO(xml))
    e = parse_attrns(StringIO(xml))
    data = []
    e.write(fileobj(data), default_namespace=dns)
    return "".join(data)

if __name__ == "__main__":
    import doctest
    doctest.testmod()

To make this work in Python3:

            for k, v in elem.attrib.copy().items():

And

from io import StringIO