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The tiny program at the end of this message runs under Python 2.5 &
30a3. Under 2 it gives the following output:
: python sax.py test.xml
('+', u'document')
('+', u'outer')
('+', u'inner')
('-', u'inner')
('-', u'outer')
('-', u'document')
Done
Under 3 it does not terminate:
: python3 sax.py test.xml
+ document
+ outer
+ inner
- inner
- outer
- document
Traceback (most recent call last):
 File "sax.py", line 19, in <module>
 parser.parse(sys.argv[1])
 File "/home/mark/opt/python30a3/lib/python3.0/xml/sax/expatreader.py",
line 107, in parse
 xmlreader.IncrementalParser.parse(self, source)
 File "/home/mark/opt/python30a3/lib/python3.0/xml/sax/xmlreader.py",
line 124, in parse
 buffer = file.read(self._bufsize)
 File "/home/mark/opt/python30a3/lib/python3.0/io.py", line 774, in read
 current = self.raw.read(to_read)
KeyboardInterrupt
The xml.sax.parser() function seems to work fine if you give it an open
file object and close the file after the call. But the documentation
says you can give it a filename, but if you do that the parser does not
terminate in Python 3 although it works fine in Python 2.
# sax.py
import sys
import xml.sax
BUG = True
class SaxHandler(xml.sax.handler.ContentHandler):
 def startElement(self, name, attributes):
 print("+", name)
 def endElement(self, name):
 print("-", name)
handler = SaxHandler()
parser = xml.sax.make_parser()
parser.setContentHandler(handler)
if BUG:
 parser.parse(sys.argv[1])
else:
 fh = open(sys.argv[1], encoding="utf8")
 parser.parse(fh)
 fh.close()
print("Done")
# end of sax.py
Here is the test file:
<?xml version="1.0" encoding="UTF-8"?>
<document>
 <outer>
 <inner>
 </inner>
 </outer>
</document>

I had to disable three unit tests in test_sax. We didn't noticed the
problem before because the tests weren't actually run. The three tests
are marked clearly with XXX and FIXME.

ISTM that this release blocker can be solved by changing
xml.sax.xmlreader.py line 122 from:
 while buffer != "":
to
 while buffer != b"":

I've a better idea:
 while buffer: 
It's faster and works for both empty bytes and str.
The patch fixes the issue and re-enables three unit tests.

The patch looks great. (I love enabling disabled tests!)

Looks like this is a duplicate of issue3590, so this patch fixes two
release blockers ;)

Benjamin will commit this.

Applied in r66203.