1 files changed, 21 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index 682ef891c..974ca6ddb 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -638,6 +638,27 @@ class Executable(Generative):
             return None
 
 
+class prefix_anon_map(dict):
+    """A map that creates new keys for missing key access.
+
+    Considers keys of the form "<ident> <name>" to produce
+    new symbols "<name>_<index>", where "index" is an incrementing integer
+    corresponding to <name>.
+
+    Inlines the approach taken by :class:`sqlalchemy.util.PopulateDict` which
+    is otherwise usually used for this type of operation.
+
+    """
+
+    def __missing__(self, key):
+        (ident, derived) = key.split(" ", 1)
+        anonymous_counter = self.get(derived, 1)
+        self[derived] = anonymous_counter + 1
+        value = derived + "_" + str(anonymous_counter)
+        self[key] = value
+        return value
+
+
 class SchemaEventTarget(object):
     """Base class for elements that are the targets of :class:`.DDLEvents`
     events.