From a2c778e2d12246cbc1da5b692a7cae23026693ce Mon Sep 17 00:00:00 2001
From: Jiaming Yuan <jm.yuan@outlook.com>
Date: Sat, 28 Nov 2020 14:18:33 -0500
Subject: [PATCH] Fix period in evaluation monitor. (#6441)

---
 python-package/xgboost/callback.py |  2 +-
 tests/python/test_callback.py      | 40 +++++++++++++++++-------------
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/python-package/xgboost/callback.py b/python-package/xgboost/callback.py
index b9583c381..e15bf699f 100644
--- a/python-package/xgboost/callback.py
+++ b/python-package/xgboost/callback.py
@@ -621,7 +621,7 @@ class EvaluationMonitor(TrainingCallback):
                     msg += self._fmt_metric(data, metric_name, score, stdv)
             msg += '\n'
 
-            if (epoch % self.period) != 0:
+            if (epoch % self.period) != 0 or self.period == 1:
                 rabit.tracker_print(msg)
                 self._latest = None
             else:
diff --git a/tests/python/test_callback.py b/tests/python/test_callback.py
index e1c5feee0..bdae94f87 100644
--- a/tests/python/test_callback.py
+++ b/tests/python/test_callback.py
@@ -22,6 +22,27 @@ class TestCallbacks:
         cls.X_valid = X[split:, ...]
         cls.y_valid = y[split:, ...]
 
+    def run_evaluation_monitor(self, D_train, D_valid, rounds, verbose_eval):
+        evals_result = {}
+        with tm.captured_output() as (out, err):
+            xgb.train({'objective': 'binary:logistic',
+                       'eval_metric': 'error'}, D_train,
+                      evals=[(D_train, 'Train'), (D_valid, 'Valid')],
+                      num_boost_round=rounds,
+                      evals_result=evals_result,
+                      verbose_eval=verbose_eval)
+            output: str = out.getvalue().strip()
+
+        pos = 0
+        msg = 'Train-error'
+        for i in range(rounds // int(verbose_eval)):
+            pos = output.find('Train-error', pos)
+            assert pos != -1
+            pos += len(msg)
+
+        assert output.find('Train-error', pos) == -1
+
+
     def test_evaluation_monitor(self):
         D_train = xgb.DMatrix(self.X_train, self.y_train)
         D_valid = xgb.DMatrix(self.X_valid, self.y_valid)
@@ -36,23 +57,8 @@ class TestCallbacks:
         assert len(evals_result['Train']['error']) == rounds
         assert len(evals_result['Valid']['error']) == rounds
 
-        with tm.captured_output() as (out, err):
-            xgb.train({'objective': 'binary:logistic',
-                       'eval_metric': 'error'}, D_train,
-                      evals=[(D_train, 'Train'), (D_valid, 'Valid')],
-                      num_boost_round=rounds,
-                      evals_result=evals_result,
-                      verbose_eval=2)
-            output: str = out.getvalue().strip()
-
-        pos = 0
-        msg = 'Train-error'
-        for i in range(rounds // 2):
-            pos = output.find('Train-error', pos)
-            assert pos != -1
-            pos += len(msg)
-
-        assert output.find('Train-error', pos) == -1
+        self.run_evaluation_monitor(D_train, D_valid, rounds, 2)
+        self.run_evaluation_monitor(D_train, D_valid, rounds, True)
 
     def test_early_stopping(self):
         D_train = xgb.DMatrix(self.X_train, self.y_train)