在Django / Python中如何减去两个日期？ [英] How do I subtract two dates in Django/Python?

问题描述

为了教我自己Django，我正在一个健身追踪器上工作。我想随着时间的推移来衡量我的体重，所以我决定使用Python的Google图表包装。 Google图表要求您将日期转换为x坐标。要做到这一点，我想通过从最后一个权重中减去第一个权重，然后使用它来计算出x坐标（例如，我可以通过结果100，并增加x坐标由每个y坐标的结果编号。）

无论如何，我需要弄清楚如何从Django datetime对象中减去到目前为止，我很惊人在谷歌和这里的堆栈。我知道PHP，但从来没有处理过OO编程，所以请原谅我的无知。这是我的模型的样子：

  class Goal（models.Model）：
 goal_weight = models.DecimalField 目标重量，
 max_digits = 4，
 decimal_places = 1）
 target_date = models.DateTimeField（目标日期到达目标）
 set_date = models.DateTimeField（你什么时候设定你的目标？）
 comments = models.TextField（blank = True）
 
 def __unicode __（self）：
 return unicode（self.goal_weight）
 
 class Weight（models.Model）：
给定日期和时间的重量。
 
 goal = models.ForeignKey（Goal）
 weight = models.DecimalField（Current Weight，
 max_digits = 4，
 decimal_places = 1）
weight_date = models.DateTimeField（Weigh-In Date）
 comment = models.TextField（blank = True）
 
 def __unicode __（self）：
 return unicode（self.weight）
 
 def recording_today（self） 
 return self.date.date （）== datetime.date.today（）
  

有关如何在视图中进行的任何想法？非常感谢！

解决方案

你可以直接减去日期，这将产生一个 datetime.timedelta 对象：

  dt = weight_now.weight_date  -  weight_then.weight_date 
  

一个 timedelta 对象有几天，秒和微秒的字段。从那里，你可以做适当的数学。例如：

  hours = dt.seconds / 60/60＃返回日期之间的小时数
 weeks = dt .days / 7＃日期之间的周数
  

I'm working on a little fitness tracker in order to teach myself Django. I want to graph my weight over time, so I've decided to use the Python Google Charts Wrapper. Google charts require that you convert your date into a x coordinate. To do this I want to take the number of days in my dataset by subtracting the first weigh-in from the last weigh-in and then using that to figure out the x coords (for example, I could 100 by the result and increment the x coord by the resulting number for each y coord.)

Anyway, I need to figure out how to subtract Django datetime objects from one another and so far, I am striking out on both google and here at the stack. I know PHP, but have never gotten a handle on OO programming, so please excuse my ignorance. Here is what my models look like:

class Goal(models.Model):
    goal_weight = models.DecimalField("Goal Weight", 
        max_digits=4, 
        decimal_places=1)
    target_date = models.DateTimeField("Target Date to Reach Goal")
    set_date = models.DateTimeField("When did you set your goal?")
    comments = models.TextField(blank=True)

    def __unicode__(self):
        return unicode(self.goal_weight)

class Weight(models.Model):
    """ Weight at a given date and time. """

    goal = models.ForeignKey(Goal)
    weight = models.DecimalField("Current Weight",
        max_digits=4, 
        decimal_places=1)
    weigh_date = models.DateTimeField("Date of Weigh-In")
    comments = models.TextField(blank=True)

    def __unicode__(self):
        return unicode(self.weight)

    def recorded_today(self):
        return self.date.date() == datetime.date.today()

Any ideas on how to proceed in the view? Thanks so much!

解决方案

You can just subtract the dates directly, which will yield a datetime.timedelta object:

dt = weight_now.weight_date - weight_then.weight_date

A timedelta object has fields for days, seconds, and microseconds. From there, you can just do the appropriate math. For example:

hours = dt.seconds / 60 / 60    # Returns number of hours between dates
weeks = dt.days / 7             # number of weeks between dates

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