“TypeError：'datetime.datetime'和'str'的实例之间不支持'>'”

Question

我正在尝试获取要展示的场地列表，然后计算即将举行的演出的数量。我在filtered_upcomingshows = [show for show in upcomingshows if show.start_time > current_time] 遇到错误。该模型将start_time 字段设置为日期时间，current_time 设置为日期时间（除非我误解了它的使用方式？）。我无法弄清楚哪个被读取为字符串。我该如何解决这个问题？

    class Show(db.Model):
  __tablename__ = 'shows'

      id = db.Column(db.Integer, primary_key=True)
      artist_id = db.Column(db.Integer, db.ForeignKey('artists.id'), nullable = False)
      venue_id = db.Column(db.Integer, db.ForeignKey('venues.id'), nullable = False)
      start_time = db.Column(db.DateTime, nullable = False)
    
      def __repr__(self):
        return '<Show {} {}>'.format(self.artist_id, self.venue_id)
   


    @app.route('/venues')
    def venues():
    
      current_time = datetime.now().strftime('%Y-%m-%d %H:%S:%M')
      venue_city_state = ''
    
      data = []
      # queries Venue db for all records
      venues = Venue.query.all()
    
      for venue in venues:
        upcomingshows = venue.shows
    
        filtered_upcomingshows = [show for show in upcomingshows if show.start_time > current_time]
    
        if venue_city_state == venue.city + venue.state:
          data[len(data) - 1]["venues"].append({
            "id": venue.id, 
            "name": venue.name,
            "num_upcoming_shows": len(filtered_upcomingshows)
          })
        else:
          venue_city_state == venue.city + venue.state
          data.append({
            "city": venue.city, 
            "state": venue.state, 
            "venues": [{
              "id": venue.id, 
              "name": venue.name, 
              "num_upcoming_shows": len(filtered_upcomingshows)
            }]
          })

Answer 1

问题是（正如解释器所说）current_time 是一个字符串，show.start_time 是一个datetime.datetime 实例。要解决此问题，您可以在定义 current_time 时删除 .strftime('%Y-%m-%d %H:%S:%M') 调用。

date.strftime(format)

返回一个表示日期的字符串，由显式格式字符串控制。引用小时、分钟或秒的格式代码将看到 0 值。有关格式化指令的完整列表，请参阅 strftime() 和 strptime() Behavior。

参考：https://docs.python.org/3/library/datetime.html#datetime.date.strftime

Answer 2

current_time = datetime.now().strftime('%Y-%m-%d %H:%S:%M')

.strftime 记录到return a string，只需取消调用即可：

current_time = datetime.now()