带pymong的Deepcopy循环

Question

所以我执行这个函数：

def getLatestRecord(self):
    transactions = self.db.transactions
    if transactions.count():
        sortedTransactions = transactions.find({"account": self.accountName}).sort("date", pymongo.DESCENDING)
        if sortedTransactions.count():
            return sortedTransactions[0]['date']

从集合中最近的记录中获取datefield。有时（还无法确定确切的原因）会导致这种回溯：

^{pr2}$

我在这里做坏事吗？在

文件示例：

{ "_id" : ObjectId("000000000000000000"), "balance" : "£2", "description" : "A payment", "moneyIn" : "", "transactionId" : "0015589241040B832015-11-03", "date" : ISODate("2015-11-03T00:00:00Z"), "moneyOut" : "£1", "account" : "MAIN ACCOUNT" }

版本：

>>> pymongo.version
'3.1'

> db.version()
3.2.4