pyDatalog：处理自定义谓词中的未绑定变量

Question

我正在编写一个pyDatalog程序来分析来自Weather Underground的天气数据（就像我自己和公司其他人的演示一样）。我写了一个自定义的谓词解析它开始和结束时间之间返回读数：

# class for the reading table. 
class Reading(Base): 
     __table__ = Table('reading', Base.metadata, autoload = True, autoload_with = engine) 
     def __repr__(self): 
     return str(self.Time) 
     # predicate to resolve 'timeBetween(X, Y, Z)' statements 
     # matches items as X where the time of day is between Y and Z (inclusive). 
     # if Y is later than Z, it returns the items not between Z and Y (exclusive). 
     # TODO - make it work where t1 and t2 are not bound. 
     # somehow needs to tell the engine to try somewhere else first. 
     @classmethod 
     def _pyD_timeBetween3(cls, dt, t1, t2): 
     if dt.is_const(): 
      # dt is already known 
      if t1.is_const() and t2.is_const(): 
      if (dt.id.Time.time() >= makeTime(t1.id)) and (dt.id.Time.time() <= makeTime(t2.id)): 
       yield (dt.id, t1.id, t2.id) 
     else: 
      # dt is an unbound variable 
      if t1.is_const() and t2.is_const(): 
      if makeTime(t2.id) > makeTime(t1.id): 
       op = 'and' 
      else: 
       op = 'or' 
      sqlWhere = "time(Time) >= '%s' %s time(Time) <= '%s'" % (t1.id, op, t2.id) 
      for instance in cls.session.query(cls).filter(sqlWhere): 
       yield(instance, t1.id, t2.id) 

这在T1和T2是绑定到特定值的情况下正常工作：

:> easterly(X) <= (Reading.WindDirection[X] == 'East') 
:> + rideAfter('11:00:00') 
:> + rideBefore('15:00:00') 
:> goodTime(X) <= rideAfter(Y) & rideBefore(Z) & Reading.timeBetween(X, Y, Z) 
:> goodTime(X) 
[(2013-02-19 11:25:00,), (2013-02-19 12:45:00,), (2013-02-19 12:50:00,), (2013-02-19 13:25:00,), (2013-02-19 14:30:00,), (2013-02-19 15:00:00,), (2013-02-19 13:35:00,), (2013-02-19 13:50:00,), (2013-02-19 12:20:00,), (2013-02-19 12:35:00,), (2013-02-19 14:05:00,), (2013-02-19 11:20:00,), (2013-02-19 11:50:00,), (2013-02-19 13:15:00,), (2013-02-19 14:55:00,), (2013-02-19 12:00:00,), (2013-02-19 13:00:00,), (2013-02-19 14:20:00,), (2013-02-19 14:15:00,), (2013-02-19 13:10:00,), (2013-02-19 12:10:00,), (2013-02-19 14:45:00,), (2013-02-19 14:35:00,), (2013-02-19 13:20:00,), (2013-02-19 11:10:00,), (2013-02-19 13:05:00,), (2013-02-19 12:55:00,), (2013-02-19 14:10:00,), (2013-02-19 13:45:00,), (2013-02-19 13:55:00,), (2013-02-19 11:05:00,), (2013-02-19 12:25:00,), (2013-02-19 14:00:00,), (2013-02-19 12:05:00,), (2013-02-19 12:40:00,), (2013-02-19 14:40:00,), (2013-02-19 11:00:00,), (2013-02-19 11:15:00,), (2013-02-19 11:30:00,), (2013-02-19 11:45:00,), (2013-02-19 13:40:00,), (2013-02-19 11:55:00,), (2013-02-19 14:25:00,), (2013-02-19 13:30:00,), (2013-02-19 12:30:00,), (2013-02-19 12:15:00,), (2013-02-19 11:40:00,), (2013-02-19 14:50:00,), (2013-02-19 11:35:00,)] 

但是如果我声明与其他顺序的条件GOODTIME规则（即，其中Y和Z是在它试图解决timeBetween点未结合的），它返回一个空集：

:> atoms('niceTime') 
:> niceTime(X) <= Reading.timeBetween(X, Y, Z) & rideAfter(Y) & rideBefore(Z) 
<pyDatalog.pyEngine.Clause object at 0x0adfa510> 
:> niceTime(X) 
[] 

钍似乎是错误的 - 两个查询应该返回相同的一组结果。

我的问题是在pyDatalog中是否有办法处理这种情况？我认为需要发生的是timeBetween谓词应该能够告诉引擎退出，并尝试在尝试这个之前先解决其他规则，但是在文档中我看不到任何这种引用。

Answer 1

pyDatalog reference说：“虽然pyDatalog语句的顺序是无差异的，但是文本内部的文字顺序是显着的”，pyDatalog的确按照它们声明的顺序来解析谓词。

话虽如此，它可能会改善pyDatalog先解析绑定变量的谓词，但我不知道为什么这很重要。