Fix ctypes.CDLL to honor handle parameter on POSIX systems

The handle parameter was being ignored in the POSIX implementation
of CDLL._load_library(), causing it to always call _dlopen() even
when a valid handle was provided. This was a regression introduced
in recent refactoring.

This commit adds the missing handle check to match the Windows
implementation behavior, and includes a regression test.

Fixes gh-143304

Author: Koolvansh07

Lib/ctypes/__init__.py

@@ -458,6 +458,8 @@ def _load_library(self, name, mode, handle, winmode):
                 if name and name.endswith(")") and ".a(" in name:
                     mode |= _os.RTLD_MEMBER | _os.RTLD_NOW
             self._name = name
+            if handle is not None:
+                return handle
             return _dlopen(name, mode)
 
     def __repr__(self):

Lib/test/test_ctypes/test_loading.py

@@ -106,6 +106,20 @@ def test_load_without_name_and_with_handle(self):
         lib = ctypes.WinDLL(name=None, handle=handle)
         self.assertIs(handle, lib._handle)
 
+    @unittest.skipIf(os.name == "nt", 'POSIX-specific test')
+    def test_load_without_name_and_with_handle_posix(self):
+        # Test that CDLL honors the handle parameter on POSIX systems
+        # This is a regression test for gh-143304
+        if libc_name is None:
+            self.skipTest('could not find libc')
+        # First load a library normally to get a handle
+        lib1 = CDLL(libc_name)
+        handle = lib1._handle
+        # Now create a new CDLL instance with the same handle
+        lib2 = CDLL(name=None, handle=handle)
+        # The handle should be used directly, not ignored
+        self.assertIs(handle, lib2._handle)
+
     @unittest.skipUnless(os.name == "nt", 'Windows-specific test')
     def test_1703286_A(self):
         # On winXP 64-bit, advapi32 loads at an address that does