Since pyexpat isn't always available in Python 2.2, allow repeated

imports of xml.parsers.expat to raise ImportError if pyexpat isn't
available.

Not needed in Python 2.3, since pyexpat is always built there.

Lib/xml/parsers/expat.py

 """Interface to the Expat non-validating XML parser."""
 __version__ = '$Revision$'
 
-from pyexpat import *
+import sys
+
+try:
+    from pyexpat import *
+except ImportError:
+    del sys.modules[__name__]
+    del sys
+    raise
+
+del sys