[Easy] Add str repr for IterationStats (#26232)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>

tests/v1/metrics/test_stats.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from vllm.v1.metrics.stats import IterationStats
+
+
+def test_iteration_stats_repr():
+    iteration_stats = IterationStats()
+    iteration_stats.iteration_timestamp = 0
+    expected_repr = ("IterationStats("
+                     "iteration_timestamp=0, "
+                     "num_generation_tokens=0, "
+                     "num_prompt_tokens=0, "
+                     "num_preempted_reqs=0, "
+                     "finished_requests=[], "
+                     "max_num_generation_tokens_iter=[], "
+                     "n_params_iter=[], "
+                     "time_to_first_tokens_iter=[], "
+                     "inter_token_latencies_iter=[], "
+                     "waiting_lora_adapters={}, "
+                     "running_lora_adapters={})")
+    assert repr(iteration_stats) == expected_repr

vllm/v1/metrics/stats.py

@@ -111,6 +111,11 @@ class IterationStats:
         self.waiting_lora_adapters: dict[str, int] = {}
         self.running_lora_adapters: dict[str, int] = {}
 
+    def __repr__(self) -> str:
+        field_to_value_str = ", ".join(f"{k}={v}"
+                                       for k, v in vars(self).items())
+        return f"{self.__class__.__name__}({field_to_value_str})"
+
     def _time_since(self, start: float) -> float:
         """Calculate an interval relative to this iteration's timestamp."""
         return self.iteration_timestamp - start