add example for using cache

examples/basic/cached_record.py

@@ -0,0 +1,34 @@
+import rltk
+
+
+class Record1(rltk.Record):
+    remove_raw_object = True
+
+    @rltk.cached_property
+    def id(self):
+        print('--> compute id:', self.raw_object['doc_id'])
+        return self.raw_object['doc_id']
+
+    @rltk.cached_property
+    def value(self):
+        print('--> compute value:', self.raw_object['doc_value'])
+        return self.raw_object['doc_value']
+
+    @property
+    def id_and_value(self):
+        print('--> compute id_and_value')
+        return self.id + '-' + self.value
+
+
+arr = [
+    {'doc_id': '1', 'doc_value': 'a'},
+    {'doc_id': '2', 'doc_value': 'b'},
+    {'doc_id': '3', 'doc_value': 'c'}
+]
+ds1 = rltk.Dataset(reader=rltk.ArrayReader(arr), record_class=Record1)
+for r1 in ds1:
+    print('------------')
+    print('id:', r1.id)
+    print('value:', r1.value)
+    print('id_and_value:', r1.id_and_value)
+    print('cache in dict:', r1.__dict__)