This script demonstrate how to access the eval metrics

import os
from typing import Any, Dict

import xgboost as xgb

CURRENT_DIR = os.path.dirname(__file__)
dtrain = xgb.DMatrix(
    os.path.join(CURRENT_DIR, "../data/agaricus.txt.train?format=libsvm")
)
dtest = xgb.DMatrix(
    os.path.join(CURRENT_DIR, "../data/agaricus.txt.test?format=libsvm")
)

param = [
    ("max_depth", 2),
    ("objective", "binary:logistic"),
    ("eval_metric", "logloss"),
    ("eval_metric", "error"),
]

num_round = 2
watchlist = [(dtest, "eval"), (dtrain, "train")]

evals_result: Dict[str, Any] = {}
bst = xgb.train(param, dtrain, num_round, watchlist, evals_result=evals_result)

print("Access logloss metric directly from evals_result:")
print(evals_result["eval"]["logloss"])

print("")
print("Access metrics through a loop:")
for e_name, e_mtrs in evals_result.items():
    print("- {}".format(e_name))
    for e_mtr_name, e_mtr_vals in e_mtrs.items():
        print("   - {}".format(e_mtr_name))
        print("      - {}".format(e_mtr_vals))

print("")
print("Access complete dictionary:")
print(evals_result)