############################################################################## # # Copyright (c) 2003 Zope Foundation and Contributors. # All Rights Reserved. # # This software is subject to the provisions of the Zope Public License, # Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution. # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS # FOR A PARTICULAR PURPOSE. # ############################################################################## """Compute a resolution order for an object and its bases """ __docformat__ = 'restructuredtext' def ro(object): """Compute a "resolution order" for an object """ return mergeOrderings([_flatten(object)]) def mergeOrderings(orderings, seen=None): """Merge multiple orderings so that within-ordering order is preserved Orderings are constrained in such a way that if an object appears in two or more orderings, then the suffix that begins with the object must be in both orderings. For example: >>> mergeOrderings([ ... ['x', 'y', 'z'], ... ['q', 'z'], ... [1, 3, 5], ... ['z'] ... ]) ['x', 'y', 'q', 1, 3, 5, 'z'] """ if seen is None: seen = {} result = [] orderings.reverse() for ordering in orderings: ordering = list(ordering) ordering.reverse() for o in ordering: if o not in seen: seen[o] = 1 result.append(o) result.reverse() return result def _flatten(ob): result = [ob] i = 0 for ob in iter(result): i += 1 # The recursive calls can be avoided by inserting the base classes # into the dynamically growing list directly after the currently # considered object; the iterator makes sure this will keep working # in the future, since it cannot rely on the length of the list # by definition. result[i:i] = ob.__bases__ return result