new structure for ptychoengine

ptycho/ptycho_example.py

@@ -4,15 +4,17 @@ import random
 from ptycho.base import PtychoEngine
 
 class ExamplePtychoEngine(PtychoEngine):
-
-    # initialize job/engine-specific variables here
-    # e.g. self.output_dir
     
     def __init__(self, config):
         super().__init__(config)
-        self._metric = 0.0
 
     # run single ptychography job based on `config`
     def run(self, run_id="") -> None:
         print(f"[{run_id}] [ExamplePtychoEngine] Sleeping for 0.1 second.")
         time.sleep(0.1)
+
+    def metric(self, names):
+        if isinstance(names, (list, tuple)):
+            return [0.0] * len(names)
+        else:
+            return 0.0