reports: Add BaseODS.set_custom_property() method.

conservancy_beancount/reports/core.py

@@ -1052,6 +1052,37 @@ class BaseODS(BaseSpreadsheet[RT, ST], metaclass=abc.ABCMeta):
 
     ### Properties
 
+    def set_custom_property(self,
+                            name: str,
+                            value: Any,
+                            valuetype: Optional[str]=None,
+    ) -> odf.meta.UserDefined:
+        if valuetype is None:
+            if isinstance(value, bool):
+                valuetype = 'boolean'
+            elif isinstance(value, (datetime.date, datetime.datetime)):
+                valuetype = 'date'
+            elif isinstance(value, (int, float, Decimal)):
+                valuetype = 'float'
+        if not isinstance(value, str):
+            if valuetype == 'boolean':
+                value = 'true' if value else 'false'
+            elif valuetype == 'date':
+                value = value.isoformat()
+            else:
+                value = str(value)
+        retval = self.ensure_child(self.document.meta, odf.meta.UserDefined, name=name)
+        if valuetype is None:
+            try:
+                retval.removeAttribute('valuetype')
+            except KeyError:
+                pass
+        else:
+            retval.setAttribute('valuetype', valuetype)
+        retval.childNodes.clear()
+        retval.addText(value)
+        return retval
+
     def set_properties(self, *,
                        created: Optional[datetime.datetime]=None,
                        generator: str='conservancy_beancount',