'Implement this method in a subclass such that it returns
a serializable object for ``o``, or calls the base implementation
(to raise a ``TypeError``).
For example, to support arbitrary iterators, you could
implement default like this::
def default(self, o):
try:
iterable = iter(o)
except TypeError:
pass
else:
return list(iterable)
return JSONEncoder.default(self, o)'

def default(self, o):

    raise TypeError((repr(o) + '    is    not    JSON    serializable'))
