def get_handler(self, operation_id):
handler = (<EOL>self.handlers.get(operation_id)<EOL>or self.handlers.get(snake_case(operation_id))<EOL>)<EOL>if handler:<EOL><INDENT>return handler<EOL><DEDENT>raise MissingHandler(<EOL>'<STR_LIT>' % (operation_id, snake_case(operation_id))<EOL>)<EOL>
Get the handler function for a given operation.

To remain Pythonic, both the original and the snake_cased version of the operation ID are
supported.

This could be overridden in a subclass.

:param operation_id: Operation ID.
:return: Handler function
:rtype: function