Merge pull request #26 from zblz/report-format-version

Write lens report format version to report and validate it on load

lens/summarise.py

@@ -26,8 +26,19 @@ class EmptyDataFrameError(Exception):
     pass
 
 
-def _validate_report(report):
+def _validate_report(report, schema_version):
     """Validates a dict report"""
+    report_schema_version = report.get('_schema_version')
+    if (report_schema_version is not None and
+            report_schema_version != schema_version):
+        raise LensSummaryError('The version of the report schema `{}` does '
+                               'not match the schema version `{}` supported '
+                               'by this version of lens {}.'.format(
+                                   report_schema_version,
+                                   schema_version,
+                                   __version__
+                               ))
+
     columns = report['_columns']
     column_props = report['column_properties']
     num_cols = [col for col in columns if (column_props[col]['numeric'])]
@@ -60,11 +71,16 @@ class Summary(object):
     in a Jupyter notebook.
 
     """
+    schema_version = 1
+
     def __init__(self, report):
         if not isinstance(report, dict):
             raise TypeError('report argument must be a dict')
 
-        _validate_report(report)
+        if '_schema_version' not in report.keys():
+            report['_schema_version'] = self.schema_version
+
+        _validate_report(report, schema_version=self.schema_version)
         self._report = report
 
     @staticmethod