Use sys.base_prefix instead of sys.prefix

doc/build.rst

@@ -259,7 +259,7 @@ There are several ways to build and install the package from source:
 
     import sys
     import pathlib
-    libpath = pathlib.Path(sys.prefix).joinpath("lib", "libxgboost.so")
+    libpath = pathlib.Path(sys.base_prefix).joinpath("lib", "libxgboost.so")
     assert libpath.exists()
 
   Then pass ``use_system_libxgboost=True`` option to ``pip install``:

python-package/packager/nativelib.py

@@ -132,8 +132,8 @@ def locate_or_build_libxgboost(
 
     if build_config.use_system_libxgboost:
         # Find libxgboost from system prefix
-        sys_prefix = pathlib.Path(sys.prefix).absolute().resolve()
-        libxgboost_sys = sys_prefix / "lib" / _lib_name()
+        sys_base_prefix = pathlib.Path(sys.base_prefix).absolute().resolve()
+        libxgboost_sys = sys_base_prefix / "lib" / _lib_name()
         if not libxgboost_sys.exists():
             raise RuntimeError(
                 f"use_system_libxgboost was specified but {_lib_name()} is "

python-package/xgboost/libpath.py

@@ -27,7 +27,7 @@ def find_lib_path() -> List[str]:
         os.path.join(curr_path, os.path.pardir, os.path.pardir, "lib"),
         # use libxgboost from a system prefix, if available.  This should be the last
         # option.
-        os.path.join(sys.base_prefix, 'lib'),
+        os.path.join(sys.base_prefix, "lib"),
     ]
 
     if sys.platform == "win32":
@@ -62,8 +62,8 @@ def find_lib_path() -> List[str]:
             + ("\n- ".join(dll_path))
             + "\nXGBoost Python package path: "
             + curr_path
-            + "\nsys.prefix: "
-            + sys.prefix
+            + "\nsys.base_prefix: "
+            + sys.base_prefix
             + "\nSee: "
             + link
             + " for installing XGBoost."