[meld] dirdiff: Rework CanonicalListing to be marginally less odd

[Kai Willadsen <kaiw src gnome org>]

commit 8b9b439f61844ae49c6ccb190c4d1aec2f874145
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Dec 17 09:22:38 2017 +1000

    dirdiff: Rework CanonicalListing to be marginally less odd
    
    This is still a deeply odd class doing a weird thing inefficiently.
    
    Oh well.

 meld/dirdiff.py | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/meld/dirdiff.py b/meld/dirdiff.py
index b9a2848d..e76417df 100644
--- a/meld/dirdiff.py
+++ b/meld/dirdiff.py
@@ -232,10 +232,16 @@ class CanonicalListing(object):
             self.errors.append((pane, item, self.items[ci][pane]))
 
     def get(self):
-        first = lambda seq: next(s for s in seq if s)
-        filled = lambda seq: tuple([s or first(seq) for s in seq])
+        def filled(seq):
+            fill_value = next(s for s in seq if s)
+            return tuple(s or fill_value for s in seq)
+
         return sorted(filled(v) for v in self.items.values())
 
+    @staticmethod
+    def canonicalize_lower(element):
+        return element.lower()
+
 
 class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
     """Two or three way folder comparison"""
@@ -704,7 +710,7 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
 
             canonicalize = None
             if self.actiongroup.get_action("IgnoreCase").get_active():
-                canonicalize = lambda x: x.lower()
+                canonicalize = CanonicalListing.canonicalize_lower
             dirs = CanonicalListing(self.num_panes, canonicalize)
             files = CanonicalListing(self.num_panes, canonicalize)