If you have more than one client, their Callback objects are the same.
>>> import smarkets.clients
>>> a = smarkets.clients.Smarkets('_')
>>> b = smarkets.clients.Smarkets('_')
>>> def h(msg): print repr(("client a received", msg))
...
>>> a.add_handler('seto.http_found', h)
# pretend b is connected and got a message...
>>> b.callbacks['seto.http_found']('example_message')
('client a received', 'example_message')
If you have more than one client, their Callback objects are the same.