Remember, Python 2.5 has this exception syntax:

try:
    raise FooException("Darn!")
except FooException, e
    print("Error: %s" % e)

The newer syntax is:

try:
    raise FooException("Darn!")
except FooException as e
    print("Error: %s" % e)

I ran into this when uploading an application to Google App Engine, which then produced this cryptic error:

<type 'exceptions.SyntaxError'>: invalid syntax (main.py, line 64)

Where line 64 is the line containing the not-yet-implemented as keyword.