如何检查日期是否过期?

我有一个包含trips信息的模型,其中一个字段是DateTimeField(),如下所示:

class Voyage(models.Model):
    voyid = models.CharField(max_length=20, primary_key= True)
    depart = models.CharField(max_length=30)
    destination = models.CharField(max_length=30)
    datedep = models.DateTimeField() #the datedep is the time and date of the trip departure 

(datedep>now),我该怎么做?