--- a/numerics/data.py	Fri Oct 03 17:48:39 2014 -0700
+++ b/numerics/data.py	Fri Oct 03 17:59:28 2014 -0700
@@ -16,7 +16,14 @@
     def __init__(self, given, expected):
         self.given = given
         self.expected = expected
-        Exception.__init__(self.__doc__.format(**self.__dict__))
+        Exception.__init__(self.__doc__.format(**self.__dict__).strip())
+
+
+class ColumnLengthException(ColumnNumberException):
+    """
+    wrong length of column: {given} given; {expected} expected
+    """
+    # XXX should share ABC, not inherit from ColumnNumberException
 
 
 class Rows(object):
@@ -56,3 +63,11 @@
 
     def __init__(self, *columns):
         self.columns = OrderedDict()  # this should be ordered
+        for name, values in columns:
+            self += (name, values)
+
+    def __iadd__(self, item):
+        column_name, values = item
+        assert column_name not in self.columns
+        
+        return self