@classmethod
def exponential(cls, lam, sam):
    """
        Visualization for an Exponential distribution
        Args:
            lam (float): parameter to an Exponential distribution
        Returns:
            image (IPython.display.Image): The image that can be displayed inline in a Jupyter notebook
        """
    if lam <= 0:
        raise ValueError(
            'For an Exponential distribution, lambda should be greater than zero.'
            )
    return cls._call_post(dist='exponential', lam=lam, sam=sam)
