Merge branch 'develop' of https://github.com/rabinnankhwa/tablib into develop

# Conflicts:
#	AUTHORS

AUTHORS

@@ -29,5 +29,6 @@ Patches and Suggestions
 - Alex Gaynor
 - James Douglass
 - Tommy Anthony
+- Rabin Nankhwa
 - Marco Dallagiacoma
 - Mathias Loesch

tablib/core.py

@@ -163,15 +163,9 @@ class Dataset(object):
         # (column, callback) tuples
         self._formatters = []
 
-        try:
-            self.headers = kwargs['headers']
-        except KeyError:
-            self.headers = None
+        self.headers = kwargs.get('headers')
 
-        try:
-            self.title = kwargs['title']
-        except KeyError:
-            self.title = None
+        self.title = kwargs.get('title')
 
         self._register_formats()
 
@@ -952,6 +946,46 @@ class Dataset(object):
         self.__headers = None
 
 
+    def subset(self, rows=None, cols=None):
+        """Returns a new instance of the :class:`Dataset`,
+        including only specified rows and columns.
+        """
+
+        # Don't return if no data
+        if not self:
+            return
+        
+        if rows is None:
+            rows = list(range(self.height))
+        
+        if cols is None:
+            cols = list(self.headers)
+            
+        #filter out impossible rows and columns
+        rows = [row for row in rows if row in range(self.height)]
+        cols = [header for header in cols if header in self.headers]
+
+        _dset = Dataset()
+        
+        #filtering rows and columns
+        _dset.headers = list(cols)
+
+        _dset._data = []
+        for row_no, row in enumerate(self._data):
+            data_row = []
+            for key in _dset.headers:
+                if key in self.headers:
+                    pos = self.headers.index(key)
+                    data_row.append(row[pos])
+                else:
+                    raise KeyError
+
+            if row_no in rows:
+                _dset.append(row=Row(data_row))
+        
+        return _dset
+
+
 
 class Databook(object):
     """A book of :class:`Dataset` objects.

test_tablib.py

@@ -811,6 +811,26 @@ class TablibTestCase(unittest.TestCase):
         self.assertTrue(data[0] == new_row)
 
 
+    def test_subset(self):
+        """Create a subset of a dataset"""
+        
+        rows = (0, 2)
+        columns = ('first_name','gpa')
+        
+        data.headers = self.headers
+
+        data.append(self.john)
+        data.append(self.george)
+        data.append(self.tom)
+        
+        #Verify data is truncated
+        subset = data.subset(rows=rows, cols=columns)
+        self.assertEqual(type(subset), tablib.Dataset)
+        self.assertEqual(subset.headers, list(columns))
+        self.assertEqual(subset._data[0].list, ['John', 90])
+        self.assertEqual(subset._data[1].list, ['Thomas', 50])
+
+
     def test_formatters(self):
         """Confirm formatters are being triggered."""