From 578de9f762e5196812fe8d8d2baf6b579d147670 Mon Sep 17 00:00:00 2001
From: Jiaming Yuan <jm.yuan@outlook.com>
Date: Fri, 8 Oct 2021 12:28:38 +0800
Subject: [PATCH] Fix cv `verbose_eval` (#7291)

---
 python-package/xgboost/training.py | 12 +++---
 tests/python/test_callback.py      | 59 ++++++++++++++++++++----------
 2 files changed, 46 insertions(+), 25 deletions(-)

diff --git a/python-package/xgboost/training.py b/python-package/xgboost/training.py
index 82b05171f0c7..c7fd14e435cf 100644
--- a/python-package/xgboost/training.py
+++ b/python-package/xgboost/training.py
@@ -472,13 +472,15 @@ def cv(params, dtrain, num_boost_round=10, nfold=3, stratified=False, folds=None
     if is_new_callback:
         assert all(isinstance(c, callback.TrainingCallback)
                    for c in callbacks), "You can't mix new and old callback styles."
-        if isinstance(verbose_eval, bool) and verbose_eval:
+        if verbose_eval:
             verbose_eval = 1 if verbose_eval is True else verbose_eval
-            callbacks.append(callback.EvaluationMonitor(period=verbose_eval,
-                                                        show_stdv=show_stdv))
+            callbacks.append(
+                callback.EvaluationMonitor(period=verbose_eval, show_stdv=show_stdv)
+            )
         if early_stopping_rounds:
-            callbacks.append(callback.EarlyStopping(
-                rounds=early_stopping_rounds, maximize=maximize))
+            callbacks.append(
+                callback.EarlyStopping(rounds=early_stopping_rounds, maximize=maximize)
+            )
         callbacks = callback.CallbackContainer(callbacks, metric=feval, is_cv=True)
     else:
         callbacks = _configure_deprecated_callbacks(
diff --git a/tests/python/test_callback.py b/tests/python/test_callback.py
index 4018bf0be256..204e5383a975 100644
--- a/tests/python/test_callback.py
+++ b/tests/python/test_callback.py
@@ -1,3 +1,4 @@
+from typing import Union
 import xgboost as xgb
 import pytest
 import os
@@ -22,29 +23,47 @@ def setup_class(cls):
         cls.X_valid = X[split:, ...]
         cls.y_valid = y[split:, ...]
 
-    def run_evaluation_monitor(self, D_train, D_valid, rounds, verbose_eval):
-        evals_result = {}
+    def run_evaluation_monitor(
+        self,
+        D_train: xgb.DMatrix,
+        D_valid: xgb.DMatrix,
+        rounds: int,
+        verbose_eval: Union[bool, int]
+    ):
+        def check_output(output: str) -> None:
+            if int(verbose_eval) == 1:
+                # Should print each iteration info
+                assert len(output.split('\n')) == rounds
+            elif int(verbose_eval) > rounds:
+                # Should print first and latest iteration info
+                assert len(output.split('\n')) == 2
+            else:
+                # Should print info by each period additionaly to first and latest
+                # iteration
+                num_periods = rounds // int(verbose_eval)
+                # Extra information is required for latest iteration
+                is_extra_info_required = num_periods * int(verbose_eval) < (rounds - 1)
+                assert len(output.split('\n')) == (
+                    1 + num_periods + int(is_extra_info_required)
+                )
+
+        evals_result: xgb.callback.TrainingCallback.EvalsLog = {}
+        params = {'objective': 'binary:logistic', 'eval_metric': 'error'}
         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)
+            xgb.train(
+                params, 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()
+            check_output(output)
 
-        if int(verbose_eval) == 1:
-            # Should print each iteration info
-            assert len(output.split('\n')) == rounds
-        elif int(verbose_eval) > rounds:
-            # Should print first and latest iteration info
-            assert len(output.split('\n')) == 2
-        else:
-            # Should print info by each period additionaly to first and latest iteration
-            num_periods = rounds // int(verbose_eval)
-            # Extra information is required for latest iteration
-            is_extra_info_required = num_periods * int(verbose_eval) < (rounds - 1)
-            assert len(output.split('\n')) == 1 + num_periods + int(is_extra_info_required)
+        with tm.captured_output() as (out, err):
+            xgb.cv(params, D_train, num_boost_round=rounds, verbose_eval=verbose_eval)
+            output = out.getvalue().strip()
+            check_output(output)
 
     def test_evaluation_monitor(self):
         D_train = xgb.DMatrix(self.X_train, self.y_train)