“类型错误：‘NoneType’类型的参数不可迭代”？

这是我编写的一些Python代码，用于生成随机扑克手牌，只是为了好玩/为了挑战，但是当我尝试运行它时，我在“如果手中有牌”这一行上收到错误。发生了什么事，为什么会发生这种情况，特别是因为该行没有迭代？

import random
def pokerHand():
    hand = ["This is your hand:"]
    x = 0
    while x < 5:
        cardNum = random.randrange(13) + 1
        if cardNum == 1:
            cardNum = "Ace of "
        elif cardNum == 11:
            cardNum = "Jack of "
        elif cardNum == 13:
            cardNum = "King of "
        elif cardNum == 12:
        cardNum = "Queen of "
        else:
            cardNum = str(cardNum) + " of "
        cardSuit = random.randrange(4)
        if cardSuit == 0:
            cardSuit = "Clubs"
        elif cardSuit == 1:
            cardSuit = "Diamonds"
        elif cardSuit == 3:
            cardSuit = "Hearts"
        elif cardSuit == 2:
            cardSuit = "Spades"
        card = cardNum + cardSuit
        if card in hand: #<the line of error
            pass
        else:
            hand = hand.append(card)
            x = x + 1
    for xx in hand:
        print xx

hand = hand.append(card)

append不返回任何内容。将其更改为：

hand.append(card)