546 

   547 # selector base classes and operations ########################################

   548 class Selector(object):

   549     """base class for selector classes providing implementation

   550     for operators ``&`` and ``|``

   551 

   552     This class is only here to give access to binary operators, the

   553     selector logic itself should be implemented in the __call__ method

   554     """

   555     def __init__(self, *selectors):

   556         self.selectors = self.merge_selectors(selectors)

   557 

   558     @classmethod

   559     def merge_selectors(cls, selectors):

   560         """merge selectors when possible :

   561 

   562         AndSelector(AndSelector(sel1, sel2), AndSelector(sel3, sel4))

   563         ==> AndSelector(sel1, sel2, sel3, sel4)

   564         """

   565         merged_selectors = []

   566         for selector in selectors:

   567             if isinstance(selector, cls):

   568                 merged_selectors += selector.selectors

   569             else:

   570                 merged_selectors.append(selector)

   571         return merged_selectors

   572         

   573     def __and__(self, other):

   574         return AndSelector(self, other)

   575 

   576     def __or__(self, other):

   577         return OrSelector(self, other)

   578 

   579     __ror__ = __or__    # for cases like (function | selector)

   580     __rand__ = __and__  # for cases like (function & selector)

   581     # XXX (function | function) or (function & function) not managed yet

   582 

   583     def __call__(self, cls, *args, **kwargs):

   584         return NotImplementedError("selector %s must implement its logic "

   585                                    "in its __call__ method" % self.__class__.__name__)

   586 

   587 

   588 class AndSelector(Selector):

   589     """and-chained selectors (formerly known as chainall)"""

   590     def __call__(self, cls, *args, **kwargs):

   591         score = 0

   592         for selector in self.selectors:

   593             partscore = selector(cls, *args, **kwargs)

   594             if not partscore:

   595                 return 0

   596             score += partscore

   597         return score

   598 

   599 

   600 class OrSelector(Selector):

   601     """or-chained selectors (formerly known as chainfirst)"""

   602     def __call__(self, cls, *args, **kwargs):

   603         for selector in self.selectors:

   604             partscore = selector(cls, *args, **kwargs)

   605             if partscore:

   606                 return partscore

   607         return 0