Created get_col method with tests and tutorial.rst update

Useful when you have multiple columns with the same header

docs/tutorial.rst

@@ -146,6 +146,13 @@ To do so, we access the :class:`Dataset` as if it were a standard Python diction
     >>> data['First Name']
     ['Kenneth', 'Bessie']
 
+You can also access the column using its index. ::
+
+    >>> d.headers
+    ['Last Name', 'First Name', 'Age']
+    >>> d.get_col(1)
+    ['Kenneth', 'Bessie']
+
 Let's find the average age. ::
 
     >>> ages = data['Age']

tablib/core.py

@@ -175,7 +175,6 @@ def __getitem__(self, key):
             else:
                 return [result.tuple for result in _results]
 
-
     def __setitem__(self, key, value):
         self._validate(value)
         self._data[key] = Row(value)
@@ -695,6 +694,12 @@ def append_col(self, col, header=None):
         self.rpush_col(col, header)
 
 
+    def get_col(self, index):
+        """Returns the column from the :class:`Dataset` at the given index."""
+
+        return [row[index] for row in self._data]
+
+
     # ----
     # Misc
     # ----

test_tablib.py

@@ -113,6 +113,22 @@ def test_header_slicing(self):
             [self.john[2], self.george[2], self.tom[2]])
 
 
+    def test_get_col(self):
+        """Verify getting columns by index"""
+
+        self.assertEqual(
+            self.founders.get_col(self.headers.index('first_name')),
+            [self.john[0], self.george[0], self.tom[0]])
+
+        self.assertEqual(
+            self.founders.get_col(self.headers.index('last_name')),
+            [self.john[1], self.george[1], self.tom[1]])
+
+        self.assertEqual(
+            self.founders.get_col(self.headers.index('gpa')),
+            [self.john[2], self.george[2], self.tom[2]])
+
+
     def test_data_slicing(self):
         """Verify slicing by data."""