Remove unneeded check leading to a regression

- the check had been incorrecty introduced to fix an issue
  ultimately related to reference counting/garbage collection
- the fix was incorrect, and that case can probably be ignored,
  as the code leading to it makes no sense

CHANGES.md

@@ -1,6 +1,12 @@
 # pyfakefs Release Notes
 The released versions correspond to PyPI releases.
 
+## Unreleased
+
+### Fixes
+* fixed a regression from version 5.4.0 that incorrectly handled files opened twice via file descriptor
+  (see [#997](../../issues/997))
+
 ## [Version 5.4.0](https://pypi.python.org/pypi/pyfakefs/5.4.0) (2024-04-07)
 Improves permission handling.
 

pyfakefs/fake_open.py

@@ -144,12 +144,6 @@ def call(
 
         newline, open_modes = self._handle_file_mode(mode, newline, open_modes)
         opened_as_fd = isinstance(file_, int)
-        if opened_as_fd and not helpers.IS_PYPY:
-            fd: int = cast(int, file_)
-            # cannot open the same file descriptor twice, except in PyPy
-            for f in self.filesystem.get_open_files(fd):
-                if isinstance(f, FakeFileWrapper) and f.opened_as_fd:
-                    raise OSError(errno.EBADF, "Bad file descriptor")
 
         # the pathlib opener is defined in a Path instance that may not be
         # patched under some circumstances; as it just calls standard open(),

pyfakefs/tests/fake_os_test.py

@@ -231,18 +231,18 @@ def test_closed_file_descriptor(self):
         self.assert_raises_os_error(errno.EBADF, self.os.fdopen, fileno2, **kwargs)
 
     def test_fdopen_twice(self):
+        # regression test for #997
         file_path = self.make_path("some_file1")
         self.create_file(file_path, contents="contents here1")
         fake_file = self.open(file_path, "r", encoding="utf8")
         fd = fake_file.fileno()
-        self.open(fd, encoding="utf8")
-        if not IS_PYPY:
-            with self.assertRaises(OSError) as cm:
-                self.open(fd, encoding="utf8")
-            self.assertEqual(errno.EBADF, cm.exception.errno)
-        else:
-            self.open(fd, encoding="utf8")
-            self.os.close(fd)
+        # note: we need to assign the files to objects,
+        # otherwise the file will be closed immediately in the CPython implementation
+        # note that this case is not (and will probably not be) handled in pyfakefs
+        file1 = self.open(fd, encoding="utf8")  # noqa: F841
+        file2 = self.open(fd, encoding="utf8")  # noqa: F841
+
+        self.os.close(fd)
 
     def test_open_fd_write_mode_for_ro_file(self):
         # Create a writable file handle to a read-only file, see #967
@@ -3159,22 +3159,6 @@ def test_listdir_impossible_without_read_permission(self):
         with self.open(file_path, encoding="utf8") as f:
             assert f.read() == "hey"
 
-    def test_fdopen_twice(self):
-        file_path1 = self.make_path("some_file1")
-        file_path2 = self.make_path("SOME_file1")
-        self.create_file(file_path1, contents="contents here1")
-
-        fake_file1 = self.open(file_path2, "r", encoding="utf8")
-        fileno1 = fake_file1.fileno()
-        self.os.fdopen(fileno1, encoding="utf8")
-        if not IS_PYPY:
-            with self.assertRaises(OSError) as cm:
-                self.open(fileno1, encoding="utf8")
-            self.assertEqual(errno.EBADF, cm.exception.errno)
-        else:
-            self.open(fileno1, encoding="utf8")
-            self.os.close(fileno1)
-
     def test_stat(self):
         directory = self.make_path("xyzzy")
         directory1 = self.make_path("XYZZY")