pricing.krb
#

Weekly package

We use the 'weekly' package when a weekly price exists and duration is greater than a week.

 
week_package
    use packages(weekly, $delta)
    when
        packages.package('weekly')
        check $delta.days >= 7
#

Daily package

We use the 'daily' package when a daily price exists an duration is lower than a week, and greater than a day.

 
day_package
    use packages(daily, $delta)
    when
        packages.package('daily')
        check $delta.days >= 1
        check $delta.days < 7
#

Daily package for week

We use the 'daily' package when a daily price exists and duration is greater than a week, only if no weekly price exists.

 
day_package_for_week
    use packages(daily, $delta)
    when
        packages.package('daily')
        check $delta.days >= 7
        notany
            packages.package('weekly')

knowledge.py
# 
import datetime
#

Importing Pyke knowledge engine

 
from pyke import knowledge_engine
#

Finding out which package apply for the duration 


      		
    

      
        

          #
        

        
Given existings packages and duration, prints which package applies
or if no package applies.

      		
      
        
def which_package(packages, duration):

      		
    

      
        

          #
        

        
We are loading Pyke rules base we have defined in pricing.krb

      		
      
        
    engine = knowledge_engine.engine((__file__, '.rules'))
    engine.activate('pricing')

      		
    

      
        

          #
        

        
Creating the facts base from the package list.

      		
      
        
    for package in packages:
        engine.assert_('packages', 'package', (package,))
        

      		
    

      
        

          #
        

        
Now, we have our rules and our facts, let's just prove that a package applies.

      		
      
        
    try:
        vals, plans = engine.prove_1_goal('pricing.packages($type, $delta)', delta=duration)
        print vals['type']

      		
    

      
        

          #
        

        
We cannot prove that any package applies therefore no package applies.

      		
      
        
    except knowledge_engine.CanNotProve:
        print "No package applies"
    

      		
    

      
        

          #
        

        
Resetting the engine is needed to be able to apply a new fact base.

      		
      
        
    engine.reset()

      		
    

      
        

          #
        

        
 Let's try with a few examples 

      		
      
        

      		
    

      
        

          #
        

        
Defining a bunch of durations

      		
      
        
a_day = datetime.timedelta(days=1)
a_week = datetime.timedelta(days=7)
less_than_a_week = datetime.timedelta(days=4)
more_than_a_week = datetime.timedelta(days=9)

      		
    

      
        

          #
        

        
This should print 'daily'

      		
      
        
print "You should read 'daily' :",
which_package(['daily', 'weekly'], a_day)

      		
    

      
        

          #
        

        
This should print 'weekly'

      		
      
        
print "You should read 'weekly' :",
which_package(['daily', 'weekly'], a_week)

      		
    

      
        

          #
        

        
This should print 'daily'

      		
      
        
print "You should read 'daily' :",
which_package(['daily', 'weekly'], less_than_a_week)

      		
    

      
        

          #
        

        
This should print 'weekly'

      		
      
        
print "You should read 'weekly' :",
which_package(['daily', 'weekly'], more_than_a_week)

      		
    

      
        

          #
        

        
This should print 'daily'

      		
      
        
print "You should read 'daily' :",
which_package(['daily'], more_than_a_week)

      		
    

      
        

          #
        

        
This should print 'No package applies'

      		
      
        
print "You should read 'No package applies' :",
which_package(['weekly'], a_day)