Adding Bigtable Row.increment_cell_value.

Similar to googleapis#1388. The API accepts integers and then encodes them
as bytes when stored in the table.

Author: dhermes

gcloud/bigtable/row.py

@@ -42,6 +42,43 @@ def __init__(self, row_key, table, filter_=None):
         self._row_key = _to_bytes(row_key)
         self._table = table
         self._filter = filter_
+        self._rule_pb_list = []
+
+    def increment_cell_value(self, column_family_id, column, int_value):
+        """Increments a value in an existing cell.
+
+        Assumes the value in the cell is stored as a 64 bit integer
+        serialized to bytes.
+
+        .. note::
+
+            This method adds a read-modify rule protobuf to the accumulated
+            read-modify rules on this :class:`Row`, but does not make an API
+            request. To actually send an API request (with the rules) to the
+            Google Cloud Bigtable API, call :meth:`commit_modifications`.
+
+        :type column_family_id: str
+        :param column_family_id: The column family that contains the column.
+                                 Must be of the form
+                                 ``[_a-zA-Z0-9][-_.a-zA-Z0-9]*``.
+
+        :type column: bytes
+        :param column: The column within the column family where the cell
+                       is located.
+
+        :type int_value: int
+        :param int_value: The value to increment the existing value in the cell
+                          by. If the targeted cell is unset, it will be treated
+                          as containing a zero. Otherwise, the targeted cell
+                          must contain an 8-byte value (interpreted as a 64-bit
+                          big-endian signed integer), or the entire request
+                          will fail.
+        """
+        column = _to_bytes(column)
+        rule_pb = data_pb2.ReadModifyWriteRule(family_name=column_family_id,
+                                               column_qualifier=column,
+                                               increment_amount=int_value)
+        self._rule_pb_list.append(rule_pb)
 
 
 class RowFilter(object):

gcloud/bigtable/test_row.py

@@ -49,6 +49,23 @@ def test_constructor_with_non_bytes(self):
         with self.assertRaises(TypeError):
             self._makeOne(row_key, None)
 
+    def test_increment_cell_value(self):
+        from gcloud.bigtable._generated import bigtable_data_pb2 as data_pb2
+
+        table = object()
+        row_key = b'row_key'
+        row = self._makeOne(row_key, table)
+        self.assertEqual(row._rule_pb_list, [])
+
+        column = b'column'
+        column_family_id = u'column_family_id'
+        int_value = 281330
+        row.increment_cell_value(column_family_id, column, int_value)
+        expected_pb = data_pb2.ReadModifyWriteRule(
+            family_name=column_family_id, column_qualifier=column,
+            increment_amount=int_value)
+        self.assertEqual(row._rule_pb_list, [expected_pb])
+
 
 class Test_BoolFilter(unittest2.TestCase):