Issue #1470548: Do not buffer XMLGenerator output.

Add test for fragment producing with XMLGenerator.

Lib/test/test_sax.py

@@ -403,6 +403,21 @@ class XmlgenTest:
         func(result)
         self.assertFalse(result.closed)
 
+    def test_xmlgen_fragment(self):
+        result = self.ioclass()
+        gen = XMLGenerator(result)
+
+        # Don't call gen.startDocument()
+        gen.startElement("foo", {"a": "1.0"})
+        gen.characters("Hello")
+        gen.endElement("foo")
+        gen.startElement("bar", {"b": "2.0"})
+        gen.endElement("bar")
+        # Don't call gen.endDocument()
+
+        self.assertEqual(result.getvalue(),
+                         '<foo a="1.0">Hello</foo><bar b="2.0"></bar>')
+
 class StringXmlgenTest(XmlgenTest, unittest.TestCase):
     ioclass = StringIO
 

Lib/xml/sax/saxutils.py

@@ -98,9 +98,13 @@ def _gettextwriter(out, encoding):
         except AttributeError:
             pass
     # wrap a binary writer with TextIOWrapper
-    return io.TextIOWrapper(buffer, encoding=encoding,
-                            errors='xmlcharrefreplace',
-                            newline='\n')
+    class UnbufferedTextIOWrapper(io.TextIOWrapper):
+        def write(self, s):
+            super(UnbufferedTextIOWrapper, self).write(s)
+            self.flush()
+    return UnbufferedTextIOWrapper(buffer, encoding=encoding,
+                                   errors='xmlcharrefreplace',
+                                   newline='\n')
 
 class XMLGenerator(handler.ContentHandler):