terom@44: """
terom@44:     Miscellaneous utilities
terom@44: """
terom@44: 
terom@59: import functools
terom@23: 
terom@59: class LazyProperty (property) :
terom@12:     """
terom@59:         Lazy-loaded properties
terom@12:     """
terom@12: 
terom@75:     ATTRNAME = '_LazyProperty_values'
terom@75: 
terom@59:     def __init__ (self, func) :
terom@59:         """
terom@59:             Initialize with no value
terom@59:         """
terom@12: 
terom@59:         super(LazyProperty, self).__init__(func)
terom@75:         
terom@75:         self.func = func
terom@75:         self.name = func.__name__
terom@19: 
terom@59:         self.value = None
terom@26: 
terom@73:     def run (self, obj) :
terom@59:         """
terom@59:             Run the background func and return the to-be-cached value
terom@59:         """
terom@28: 
terom@75:         return self.func(obj)
terom@73:  
terom@75:     def obj_dict (self, obj):
terom@75:         """
terom@75:             Get the lazy-property dict of the given obj
terom@75:         """
terom@75: 
terom@75:         dict = getattr(obj, self.ATTRNAME, None)
terom@75: 
terom@75:         if dict is None :
terom@75:             dict = {}
terom@75: 
terom@75:             setattr(obj, self.ATTRNAME, dict)
terom@75: 
terom@75:         return dict
terom@75: 
terom@73:     def get (self, obj) :
terom@73:         """
terom@73:             Return the cached value
terom@73:         """
terom@59: 
terom@75:         return self.obj_dict(obj)[self.name]
terom@73:     
terom@73:     def set (self, obj, value) :
terom@73:         """
terom@73:             Set the cached value
terom@73:         """
terom@73: 
terom@75:         self.obj_dict(obj)[self.name] = value
terom@73: 
terom@73:     def test (self, obj) :
terom@73:         """
terom@73:             Tests if a value is set
terom@73:         """
terom@73: 
terom@75:         return self.name in self.obj_dict(obj)
terom@73:        
terom@75:     def __get__ (self, obj, owner) :
terom@59:         """
terom@59:             Return the cached value if it exists, otherwise, call the func
terom@59:         """
terom@59: 
terom@75:         if not obj :
terom@75:             return self
terom@75: 
terom@75:         if not self.test(obj) :
terom@59:             # generate it
terom@73:             self.set(obj, self.run(obj))
terom@59: 
terom@73:         return self.get(obj)
terom@59: 
terom@59: class LazyIteratorProperty (LazyProperty) :
terom@59:     """
terom@59:         A lazy-loaded property that automatically converts an iterator/genexp into a list.
terom@59:     """
terom@59: 
terom@73:     def run (self, obj) :
terom@59:         """
terom@59:             Wrap LazyProperty.run to return a list
terom@59:         """
terom@59: 
terom@73:         return list(super(LazyIteratorProperty, self).run(obj))
terom@59: 
terom@59: lazy_load = LazyProperty
terom@59: lazy_load_iter = LazyIteratorProperty
terom@59: