add os.PathLike support for file paths to DMatrix and Booster Python classes (#4757)

tests/python/test_basic.py

@@ -11,6 +11,7 @@ import numpy as np
 import xgboost as xgb
 import unittest
 import json
+from pathlib import Path
 
 dpath = 'demo/data/'
 rng = np.random.RandomState(1994)
@@ -341,3 +342,92 @@ class TestBasic(unittest.TestCase):
         dtrain.get_float_info('weight')
         dtrain.get_float_info('base_margin')
         dtrain.get_uint_info('root_index')
+
+
+class TestBasicPathLike(unittest.TestCase):
+    """Unit tests using the os_fspath and pathlib.Path for file interaction."""
+
+    def test_DMatrix_init_from_path(self):
+        """Initialization from the data path."""
+        dpath = Path('demo/data')
+        dtrain = xgb.DMatrix(dpath / 'agaricus.txt.train')
+        assert dtrain.num_row() == 6513
+        assert dtrain.num_col() == 127
+
+
+    def test_DMatrix_save_to_path(self):
+        """Saving to a binary file using pathlib from a DMatrix."""
+        data = np.random.randn(100, 2)
+        target = np.array([0, 1] * 50)
+        features = ['Feature1', 'Feature2']
+
+        dm = xgb.DMatrix(data, label=target, feature_names=features)
+
+        # save, assert exists, remove file
+        binary_path = Path("dtrain.bin")
+        dm.save_binary(binary_path)
+        assert binary_path.exists()
+        Path.unlink(binary_path)
+
+
+    def test_Booster_init_invalid_path(self):
+        """An invalid model_file path should raise XGBoostError."""
+        self.assertRaises(xgb.core.XGBoostError, xgb.Booster,
+                          model_file=Path("invalidpath"))
+
+
+    def test_Booster_save_and_load(self):
+        """Saving and loading model files from paths."""
+        save_path = Path("saveload.model")
+
+        data = np.random.randn(100, 2)
+        target = np.array([0, 1] * 50)
+        features = ['Feature1', 'Feature2']
+
+        dm = xgb.DMatrix(data, label=target, feature_names=features)
+        params = {'objective': 'binary:logistic',
+                  'eval_metric': 'logloss',
+                  'eta': 0.3,
+                  'max_depth': 1}
+
+        bst = xgb.train(params, dm, num_boost_round=1)
+
+        # save, assert exists
+        bst.save_model(save_path)
+        assert save_path.exists()
+
+        def dump_assertions(dump):
+            """Assertions for the expected dump from Booster"""
+            assert len(dump) == 1, 'Exepcted only 1 tree to be dumped.'
+            assert len(dump[0].splitlines()) == 3, 'Expected 1 root and 2 leaves - 3 lines.'
+
+        # load the model again using Path
+        bst2 = xgb.Booster(model_file=save_path)
+        dump2 = bst2.get_dump()
+        dump_assertions(dump2)
+
+        # load again using load_model
+        bst3 = xgb.Booster()
+        bst3.load_model(save_path)
+        dump3= bst3.get_dump()
+        dump_assertions(dump3)
+
+        # remove file
+        Path.unlink(save_path)
+
+    def test_os_fspath(self):
+        """Core properties of the os_fspath function."""
+        # strings are returned unmodified
+        assert '' == xgb.compat.os_fspath('')
+        assert '/this/path' == xgb.compat.os_fspath('/this/path')
+
+        # bytes are returned unmodified
+        assert b'/this/path' == xgb.compat.os_fspath(b'/this/path')
+
+        # path objects are returned as string representation
+        path_test = Path('this') / 'path'
+        assert str(path_test) == xgb.compat.os_fspath(path_test)
+
+        # invalid values raise Type error
+        self.assertRaises(TypeError, xgb.compat.os_fspath, 123)
+