Adding comments to clarify HappyBase counter_inc().

Author: dhermes

gcloud/bigtable/happybase/table.py

@@ -181,11 +181,25 @@ def counter_inc(self, row, column, value=1):
             column = column.decode('utf-8')
         column_family_id, column_qualifier = column.split(':')
         row.increment_cell_value(column_family_id, column_qualifier, value)
+        # See row.commit_modifications() will return a dictionary:
+        # {
+        #     u'col-fam-id': {
+        #         b'col-name1': [
+        #             (b'cell-val', datetime.datetime(...)),
+        #             ...
+        #         ],
+        #         ...
+        #     },
+        # }
         modified_cells = row.commit_modifications()
+        # Get the cells in the modified column,
         column_cells = modified_cells[column_family_id][column_qualifier]
+        # Make sure there is exactly one cell in the column.
         if len(column_cells) != 1:
             raise ValueError('Expected server to return one modified cell.')
-        bytes_value = column_cells[0][0]
+        column_cell = column_cells[0]
+        # Get the bytes value from the column and convert it to an integer.
+        bytes_value = column_cell[0]
         int_value, = _UNPACK_I64(bytes_value)
         return int_value