def require_initialized(exception):
    """
    Decorator for API methods that should only be called after
    TradingAlgorithm.initialize.  `exception` will be raised if the method is
    called before initialize has completed.

    Examples
    --------
    @require_initialized(SomeException("Don't do that!"))
    def method(self):
        # Do stuff that should only be allowed after initialize.
    """
    def decorator(method):
        @wraps(method)
        def wrapped_method(self, *args, **kwargs):
            if not self.initialized:
                raise exception
            return method(self, *args, **kwargs)
        return wrapped_method
    return decorator