Optimize the return value of get_reverse_tree

All callers of get_reverse_tree compute the same modification of its
return value, so move that computation into get_reverse_tree.

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

britney.py

@@ -191,6 +191,7 @@ import urllib
 import apt_pkg
 
 from functools import reduce, partial
+from itertools import chain, repeat
 from operator import attrgetter
 
 if __name__ == '__main__':
@@ -1891,8 +1892,7 @@ class Britney(object):
                     # save the old binary for undo
                     undo['binaries'][p] = binaries[parch][0][binary]
                     # all the reverse dependencies are affected by the change
-                    affected.update( [ (x, parch) for x in \
-                                       self.get_reverse_tree(binary, parch, 'testing') ] )
+                    affected.update(self.get_reverse_tree(binary, parch, 'testing'))
                     # remove the provided virtual packages
                     for j in binaries[parch][0][binary][PROVIDES]:
                         key = j + "/" + parch
@@ -1916,8 +1916,7 @@ class Britney(object):
         # updates but not supported as a manual hint
         elif item.package in binaries[item.architecture][0]:
             undo['binaries'][item.package + "/" + item.architecture] = binaries[item.architecture][0][item.package]
-            affected.update( [ (x, item.architecture) for x in \
-               self.get_reverse_tree(item.package, item.architecture, 'testing') ] )
+            affected.update(self.get_reverse_tree(item.package, item.architecture, 'testing'))
             del binaries[item.architecture][0][item.package]
             self.systems[item.architecture].remove_binary(item.package)
 
@@ -1935,8 +1934,7 @@ class Britney(object):
                     # save the old binary package
                     undo['binaries'][p] = binaries[parch][0][binary]
                     # all the reverse dependencies are affected by the change
-                    affected.update( [ (x, parch) for x in \
-                                        self.get_reverse_tree(binary, parch, 'testing') ] )
+                    affected.update(self.get_reverse_tree(binary, parch, 'testing'))
                     # all the reverse conflicts and their dependency tree are affected by the change
                     for j in binaries[parch][0][binary][RCONFLICTS]:
                         key = (j, parch)
@@ -1958,8 +1956,7 @@ class Britney(object):
                             for rdep in tundo['binaries'][p][RDEPENDS]:
                                 if rdep in binaries[parch][0] and rdep not in source[BINARIES]:
                                     affected.add( (rdep, parch) )
-                                    affected.update( [ (x, parch) for x in \
-                                                        self.get_reverse_tree(rdep, parch, 'testing') ] )
+                                    affected.update(self.get_reverse_tree(rdep, parch, 'testing'))
                 # add/update the binary package
                 binaries[parch][0][binary] = self.binaries[item.suite][parch][0][binary]
                 self.systems[parch].add_binary(binary, binaries[parch][0][binary][:PROVIDES] + \
@@ -1974,8 +1971,7 @@ class Britney(object):
                         undo['virtual'][key] = binaries[parch][1][j][:]
                     binaries[parch][1][j].append(binary)
                 # all the reverse dependencies are affected by the change
-                affected.update( [ (x, parch) for x in \
-                                    self.get_reverse_tree(binary, parch, 'testing') ] )
+                affected.update(self.get_reverse_tree(binary, parch, 'testing'))
 
             # register reverse dependencies and conflicts for the new binary packages
             for p in source[BINARIES]:
@@ -2004,9 +2000,9 @@ class Britney(object):
                              if x in binaries ]
             # flatten the list-of-lists, filtering out already handled packages
             # in the process
-            rev_deps = set([ package for sublist in new_rev_deps \
-                             for package in sublist if package not in seen ])
-        return seen
+            rev_deps = set([package for package in chain.from_iterable(new_rev_deps) \
+                                 if package not in seen ])
+        return zip(seen, repeat(arch))
 
     def get_full_tree(self, pkg, arch, suite):
         """Calculate the full dependency tree for the given package