您可以直接减去日期，这将产生一个
datetime.timedelta对象：
dt = weight_now.weight_date - weight_then.weight_date
一个
timedelta对象具有几天，几秒钟和几微秒的字段。从那里，您可以进行适当的数学运算。例如：
hours = dt.seconds / 60 / 60 # Returns number of hours between datesweeks = dt.days / 7 # number of weeks between dates
