Added printing requirements

zope/interface/ro.py

@@ -0,0 +1,69 @@
+##############################################################################
+#
+# 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