Add container filters and use it to refactor get_reverse_tree

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -212,7 +212,8 @@ from excuse import Excuse
 from migrationitem import MigrationItem, HintItem
 from hints import HintCollection
 from britney import buildSystem
-from britney_util import old_libraries_format, same_source, undo_changes
+from britney_util import (old_libraries_format, same_source, undo_changes,
+                          ifilter_except, ifilter_only)
 from consts import (VERSION, SECTION, BINARIES, MAINTAINER, FAKESRC,
                    SOURCE, SOURCEVER, ARCHITECTURE, DEPENDS, CONFLICTS,
                    PROVIDES, RDEPENDS, RCONFLICTS)
@@ -2061,17 +2062,16 @@ class Britney(object):
             return frozenset()
         rev_deps = set(binaries[pkg][RDEPENDS])
         seen = set([pkg])
-        while len(rev_deps) > 0:
+
+        binfilt = ifilter_only(binaries)
+        revfilt = ifilter_except(seen)
+        flatten = chain.from_iterable
+        while rev_deps:
             # mark all of the current iteration of packages as affected
             seen |= rev_deps
             # generate the next iteration, which is the reverse-dependencies of
             # the current iteration
-            new_rev_deps = [ binaries[x][RDEPENDS] for x in rev_deps \
-                             if x in binaries ]
-            # flatten the list-of-lists, filtering out already handled packages
-            # in the process
-            rev_deps = set([package for package in chain.from_iterable(new_rev_deps) \
-                                 if package not in seen ])
+            rev_deps = set(revfilt(flatten( binaries[x][RDEPENDS] for x in binfilt(rev_deps) )))
         return izip(seen, repeat(arch))
 
     def _check_packages(self, binaries, systems, arch, affected, skip_archall, nuninst, pkg):

britney_util.py

@@ -5,6 +5,7 @@
 #                         Andreas Barth <aba@debian.org>
 #                         Fabio Tranchitella <kobold@debian.org>
 # Copyright (C) 2010-2012 Adam D. Barratt <adsb@debian.org>
+# Copyright (C) 2012 Niels Thykier <niels@thykier.net>
 
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -16,6 +17,9 @@
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 
+
+from functools import partial
+from itertools import ifilter, ifilterfalse
 import re
 from consts import BINARIES, PROVIDES
 
@@ -44,6 +48,32 @@ def same_source(sv1, sv2, binnmu_re=binnmu_re):
     return 0
 
 
+def ifilter_except(container, iterable=None):
+    """Filter out elements in container
+
+    If given an iterable it returns a filtered iterator, otherwise it
+    returns a function to generate filtered iterators.  The latter is
+    useful if the same filter has to be (re-)used on multiple
+    iterators that are not known on beforehand.
+    """
+    if iterable is not None:
+        return ifilterfalse(container.__contains__, iterable)
+    return partial(ifilterfalse, container.__contains__)
+
+
+def ifilter_only(container, iterable=None):
+    """Filter out elements in which are not in container
+
+    If given an iterable it returns a filtered iterator, otherwise it
+    returns a function to generate filtered iterators.  The latter is
+    useful if the same filter has to be (re-)used on multiple
+    iterators that are not known on beforehand.
+    """
+    if iterable is not None:
+        return ifilter(container.__contains__, iterable)
+    return partial(ifilter, container.__contains__)
+
+
 def undo_changes(lundo, systems, sources, binaries,
                  BINARIES=BINARIES, PROVIDES=PROVIDES):
     """Undoes one or more changes to testing