- rework the -r flag on history to make use of existing walk_revisions();

this way we get at relative revisions, error handling, etc.
- don't run environment for history command unless "current" was requested;
running the environment modifies output with logging, might access multiple
dbs, etc., so don't get into it if not needed
- add test suite for commands, start with history output
- document/changelog for history -r feature
- fix sys.stdout writing for py3k
- one more with_statement future not needed

1 files changed, 6 insertions, 4 deletions

diff --git a/alembic/script.py b/alembic/script.py
index 229407b..637a749 100644
--- a/alembic/script.py
+++ b/alembic/script.py
@@ -56,20 +56,22 @@ class ScriptDirectory(object):
                                     "found in configuration.")
         return ScriptDirectory(
                     util.coerce_resource_to_filename(script_location),
-                    file_template = config.get_main_option(
+                    file_template=config.get_main_option(
                                         'file_template',
                                         _default_file_template)
                     )
 
-    def walk_revisions(self):
+    def walk_revisions(self, base="base", head="head"):
         """Iterate through all revisions.
 
         This is actually a breadth-first tree traversal,
         with leaf nodes being heads.
 
         """
-        heads = set(self.get_heads())
-        base = self.get_revision("base")
+        if head == "head":
+            heads = set(self.get_heads())
+        else:
+            heads = set([head])
         while heads:
             todo = set(heads)
             heads = set()