The first data in the list self.datas[0] is the default data for trading operations and to keep all strategy elements synchronized (it’s the system clock) 如果同时加载了两个数据来源，则第二个数据源使用datas[1]读取。
The stake is provided behind the scenes by a position sizer which uses a fixed stake, being the default “1”. 这个股本是由头寸规模在后台决定的，他是一个固定的股本，默认值是1.
Already in the market 已经持有
The time is gone and testing a strategy against a fully formed and closed bar is good, but it could be better. 时间一去不复返了，针对一个完全成形的封闭式bar测试一种策略是好的，但也可能更好 This is where Data Replay comes in to help. 这就是数据重放的作用。
