有人能帮我把这个函数写在一行吗？

Question

这是我的解决办法。不雅观。请帮忙。你知道吗

def calculateHandlen(hand):
    """ 
    Returns the length (number of letters) in the current hand.

    hand: dictionary (string int)
    returns: integer
    """
    num = 0
    keyS = hand.keys()
    for key in keyS:
        if hand[key] > 0:
            num += hand[key]
    return num

Answer 1

def calculateHandlen(hand):
    return sum(v for v in hand.values() if v > 0)

但为什么呢？你知道吗