Add a cmp_sort_key class which makes it easier to port code for python-3.0

compatibility. It works by generating key objects which use the given cmp
function to implement their __lt__ method. (trunk r12571)

svn path=/main/branches/2.1.6/; revision=12852

diff --git a/pym/portage/util.py b/pym/portage/util.py
index ab72140703f130bc9ac376f9e399a428a47f8a54..def0d3e40f3a24d694b096abb11d508a2f1aabae 100644 (file)
--- a/pym/portage/util.py
+++ b/pym/portage/util.py
@@ -605,6 +605,42 @@ def dump_traceback(msg, noiselevel=1):
                writemsg(error+"\n", noiselevel=noiselevel)
        writemsg("====================================\n\n", noiselevel=noiselevel)
 
+class cmp_sort_key(object):
+       """
+       In python-3.0 the list.sort() method no longer has a "cmp" keyword
+       argument. This class acts as an adapter which converts a cmp function
+       into one that's suitable for use as the "key" keyword argument to
+       list.sort(), making it easier to port code for python-3.0 compatibility.
+       It works by generating key objects which use the given cmp function to
+       implement their __lt__ method.
+       """
+       __slots__ = ("_cmp_func",)
+
+       def __init__(self, cmp_func):
+               """
+               @type cmp_func: callable which takes 2 positional arguments
+               @param cmp_func: A cmp function.
+               """
+               self._cmp_func = cmp_func
+
+       def __call__(self, lhs):
+               return self._cmp_key(self._cmp_func, lhs)
+
+       class _cmp_key(object):
+               __slots__ = ("_cmp_func", "_obj")
+
+               def __init__(self, cmp_func, obj):
+                       self._cmp_func = cmp_func
+                       self._obj = obj
+
+               def __lt__(self, other):
+                       if not isinstance(other, self.__class__):
+                               raise TypeError("Expected type %s, got %s" % \
+                                       (self.__class__, other.__class__))
+                       if self._cmp_func(self._obj, other._obj) < 0:
+                               return True
+                       return False
+
 def unique_array(s):
        """lifted from python cookbook, credit: Tim Peters
        Return a list of the elements in s in arbitrary order, sans duplicates"""