<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def entropy(rho: Density, base: float = None) -> float: """ Returns the von-Neumann entropy of a mixed quantum state. Args: rho: A density matrix base: Optional logarithm base. Default is base e, and entropy is measures in nats. For bits set base to 2. Returns: The von-Neumann entropy of rho """

    op = asarray(rho.asoperator())
    probs = np.linalg.eigvalsh(op)
    probs = np.maximum(probs, 0.0)  # Compensate for floating point errors
    return scipy.stats.entropy(probs, base=base)