Enhance metric evaluation in DesktopEnv

- Add assertions to ensure the number of metrics matches the number of result and expected getters.
- Refactor metric calculation logic to handle cases with and without expected values more clearly.
- Improve comments for better understanding of single and multiple metric evaluations.

desktop_env/desktop_env.py

@@ -274,7 +274,11 @@ class DesktopEnv(gym.Env):
                 return 0
 
         if type(self.metric) == list:
+            # Multiple metrics to evaluate whether the task is successfully completed
             results = []
+            assert len(self.metric) == len(self.result_getter), "The number of metrics and result getters must be the same"
+            if "expected" in self.evaluator:
+                assert len(self.metric) == len(self.expected_getter), "The number of metrics and expected getters must be the same"
             for idx, metric in enumerate(self.metric):
                 try:
                     config = self.evaluator["result"][idx]
@@ -284,12 +288,11 @@ class DesktopEnv(gym.Env):
                     if self.metric_conj == 'and':
                         return 0
 
-                expected = self.evaluator["expected"][idx]
-                expected_state = self.expected_getter[idx](self, expected) if expected else None
-
-                metric: int = metric(result_state, expected_state,
-                                     **self.metric_options[idx]) if expected_state is not None \
-                    else metric(result_state, **self.metric_options[idx])
+                if "expected" in self.evaluator:
+                    expected_state = self.expected_getter[idx](self, self.evaluator["expected"][idx])
+                    metric: int = metric(result_state, expected_state, **self.metric_options[idx])
+                else:
+                    metric: int = metric(result_state, **self.metric_options[idx])
 
                 if self.metric_conj == 'and' and float(metric) == 0.0:
                     return 0
@@ -297,20 +300,21 @@ class DesktopEnv(gym.Env):
                     return 1
                 else:
                     results.append(metric)
+
             return sum(results) / len(results) if self.metric_conj == 'and' else max(results)
         else:
+            # Single metric to evaluate whether the task is successfully completed
             try:
                 result_state = self.result_getter(self, self.evaluator["result"])
             except FileNotFoundError:
                 logger.error("File not found!")
                 return 0
 
-            expected_state = self.expected_getter(self, self.evaluator["expected"]) if "expected" in self.evaluator \
-                else None
-
-            metric: float = self.metric(result_state, expected_state,
-                                        **self.metric_options) if expected_state is not None \
-                else self.metric(result_state, **self.metric_options)
+            if "expected" in self.evaluator:
+                expected_state = self.expected_getter(self, self.evaluator["expected"])
+                metric: float = self.metric(result_state, expected_state, **self.metric_options)
+            else:
+                metric: float = self.metric(result_state, **self.metric_options)
 
         return metric