added ability to append new column passing a callable as the value that will be applied to every row; w/ test

tablib/core.py

@@ -177,6 +177,15 @@ class Dataset(object):
 			self._validate(row)
 			self._data.append(tuple(row))
 		elif col is not None:
+			col = list(col)
+			if self.headers:
+				header = [col.pop(0)]
+			else:
+				header = []
+			if len(col) == 1 and callable(col[0]):
+				col = map(col[0], self._data)
+			col = tuple(header + col)
+				
 			self._validate(col=col)
 
 			if self.headers:

test_tablib.py

@@ -102,6 +102,13 @@ class TablibTestCase(unittest.TestCase):
 
 		self.assertRaises(tablib.InvalidDimensions, data.append, col=new_col)
 
+	def test_add_callable_column(self):
+		"""Verify adding column with values specified as callable."""
+		new_col = ['first_again', lambda x: x[0]]
+		self.founders.append(col=new_col)
+
+		self.assertTrue(map(lambda x: x[0] == x[-1], self.founders))
+
 
 	def test_header_slicing(self):
 		"""Verify slicing by headers."""