[python] migrate to pathlib in create_nuget.py (#4422)

.nuget/create_nuget.py

 # coding: utf-8
 """Script for generating files with NuGet package metadata."""
 import datetime
-import os
 import sys
-from distutils.file_util import copy_file
+from pathlib import Path
+from shutil import copyfile
 
 if __name__ == "__main__":
-    source = sys.argv[1]
-    current_dir = os.path.abspath(os.path.dirname(__file__))
-    linux_folder_path = os.path.join(current_dir, "runtimes", "linux-x64", "native")
-    if not os.path.exists(linux_folder_path):
-        os.makedirs(linux_folder_path)
-    osx_folder_path = os.path.join(current_dir, "runtimes", "osx-x64", "native")
-    if not os.path.exists(osx_folder_path):
-        os.makedirs(osx_folder_path)
-    windows_folder_path = os.path.join(current_dir, "runtimes", "win-x64", "native")
-    if not os.path.exists(windows_folder_path):
-        os.makedirs(windows_folder_path)
-    build_folder_path = os.path.join(current_dir, "build")
-    if not os.path.exists(build_folder_path):
-        os.makedirs(build_folder_path)
-    copy_file(os.path.join(source, "lib_lightgbm.so"), os.path.join(linux_folder_path, "lib_lightgbm.so"))
-    copy_file(os.path.join(source, "lib_lightgbm.dylib"), os.path.join(osx_folder_path, "lib_lightgbm.dylib"))
-    copy_file(os.path.join(source, "lib_lightgbm.dll"), os.path.join(windows_folder_path, "lib_lightgbm.dll"))
-    copy_file(os.path.join(source, "lightgbm.exe"), os.path.join(windows_folder_path, "lightgbm.exe"))
-    version = open(os.path.join(current_dir, os.path.pardir, 'VERSION.txt')).read().strip().replace('rc', '-rc')
+    source = Path(sys.argv[1])
+    current_dir = Path(__file__).parent.absolute()
+    linux_folder_path = current_dir / "runtimes" / "linux-x64" / "native"
+    linux_folder_path.mkdir(parents=True, exist_ok=True)
+    osx_folder_path = current_dir / "runtimes" / "osx-x64" / "native"
+    osx_folder_path.mkdir(parents=True, exist_ok=True)
+    windows_folder_path = current_dir / "runtimes" / "win-x64" / "native"
+    windows_folder_path.mkdir(parents=True, exist_ok=True)
+    build_folder_path = current_dir / "build"
+    build_folder_path.mkdir(parents=True, exist_ok=True)
+    copyfile(source / "lib_lightgbm.so", linux_folder_path / "lib_lightgbm.so")
+    copyfile(source / "lib_lightgbm.dylib", osx_folder_path / "lib_lightgbm.dylib")
+    copyfile(source / "lib_lightgbm.dll", windows_folder_path / "lib_lightgbm.dll")
+    copyfile(source / "lightgbm.exe", windows_folder_path / "lightgbm.exe")
+    version = (current_dir.parent / 'VERSION.txt').read_text(encoding='utf-8').strip().replace('rc', '-rc')
     nuget_str = rf"""<?xml version="1.0"?>
     <package xmlns="http://schemas.microsoft.com/packaging/2013/05/nuspec.xsd">
     <metadata>
@@ -79,9 +75,6 @@ if __name__ == "__main__":
     </Target>
     </Project>
     """
-    with open(os.path.join(current_dir, "LightGBM.nuspec"), "w") as nuget_file:
-        nuget_file.write(nuget_str)
-    with open(os.path.join(current_dir, "build", "LightGBM.props"), "w") as prop_file:
-        prop_file.write(prop_str)
-    with open(os.path.join(current_dir, "build", "LightGBM.targets"), "w") as target_file:
-        target_file.write(target_str)
+    (current_dir / "LightGBM.nuspec").write_text(nuget_str, encoding='utf-8')
+    (current_dir / "build" / "LightGBM.props").write_text(prop_str, encoding='utf-8')
+    (current_dir / "build" / "LightGBM.targets").write_text(target_str, encoding='utf-8')