gh-82626: Emit a warning when bool is used as a file descriptor (GH-111275)

Doc/whatsnew/3.13.rst

@@ -145,6 +145,11 @@ Other Language Changes
   is rejected when the global is used in the :keyword:`else` block.
   (Contributed by Irit Katriel in :gh:`111123`.)
 
+* Many functions now emit a warning if a boolean value is passed as
+  a file descriptor argument.
+  This can help catch some errors earlier.
+  (Contributed by Serhiy Storchaka in :gh:`82626`.)
+
 * Added a new environment variable :envvar:`PYTHON_FROZEN_MODULES`. It
   determines whether or not frozen modules are ignored by the import machinery,
   equivalent of the :option:`-X frozen_modules <-X>` command-line option.

Lib/_pyio.py

@@ -1495,6 +1495,11 @@ class FileIO(RawIOBase):
         if isinstance(file, float):
             raise TypeError('integer argument expected, got float')
         if isinstance(file, int):
+            if isinstance(file, bool):
+                import warnings
+                warnings.warn("bool is used as a file descriptor",
+                              RuntimeWarning, stacklevel=2)
+                file = int(file)
             fd = file
             if fd < 0:
                 raise ValueError('negative file descriptor')

Lib/test/test_fileio.py

@@ -484,6 +484,14 @@ class OtherFileTests:
             import msvcrt
             self.assertRaises(OSError, msvcrt.get_osfhandle, make_bad_fd())
 
+    def testBooleanFd(self):
+        for fd in False, True:
+            with self.assertWarnsRegex(RuntimeWarning,
+                    'bool is used as a file descriptor') as cm:
+                f = self.FileIO(fd, closefd=False)
+            f.close()
+            self.assertEqual(cm.filename, __file__)
+
     def testBadModeArgument(self):
         # verify that we get a sensible error message for bad mode argument
         bad_mode = "qwerty"

Lib/test/test_genericpath.py

@@ -165,6 +165,12 @@ class GenericTest:
             os.close(w)
         self.assertFalse(self.pathmodule.exists(r))
 
+    def test_exists_bool(self):
+        for fd in False, True:
+            with self.assertWarnsRegex(RuntimeWarning,
+                    'bool is used as a file descriptor'):
+                self.pathmodule.exists(fd)
+
     def test_isdir(self):
         filename = os_helper.TESTFN
         bfilename = os.fsencode(filename)

Lib/test/test_os.py

@@ -2195,12 +2195,15 @@ class Win32ErrorTests(unittest.TestCase):
 class TestInvalidFD(unittest.TestCase):
     singles = ["fchdir", "dup", "fdatasync", "fstat",
                "fstatvfs", "fsync", "tcgetpgrp", "ttyname"]
+    singles_fildes = {"fchdir", "fdatasync", "fsync"}
     #singles.append("close")
     #We omit close because it doesn't raise an exception on some platforms
     def get_single(f):
         def helper(self):
             if  hasattr(os, f):
                 self.check(getattr(os, f))
+                if f in self.singles_fildes:
+                    self.check_bool(getattr(os, f))
         return helper
     for f in singles:
         locals()["test_"+f] = get_single(f)
@@ -2214,8 +2217,16 @@ class TestInvalidFD(unittest.TestCase):
             self.fail("%r didn't raise an OSError with a bad file descriptor"
                       % f)
 
+    def check_bool(self, f, *args, **kwargs):
+        with warnings.catch_warnings():
+            warnings.simplefilter("error", RuntimeWarning)
+            for fd in False, True:
+                with self.assertRaises(RuntimeWarning):
+                    f(fd, *args, **kwargs)
+
     def test_fdopen(self):
         self.check(os.fdopen, encoding="utf-8")
+        self.check_bool(os.fdopen, encoding="utf-8")
 
     @unittest.skipUnless(hasattr(os, 'isatty'), 'test needs os.isatty()')
     def test_isatty(self):
@@ -2277,11 +2288,14 @@ class TestInvalidFD(unittest.TestCase):
     def test_fpathconf(self):
         self.check(os.pathconf, "PC_NAME_MAX")
         self.check(os.fpathconf, "PC_NAME_MAX")
+        self.check_bool(os.pathconf, "PC_NAME_MAX")
+        self.check_bool(os.fpathconf, "PC_NAME_MAX")
 
     @unittest.skipUnless(hasattr(os, 'ftruncate'), 'test needs os.ftruncate()')
     def test_ftruncate(self):
         self.check(os.truncate, 0)
         self.check(os.ftruncate, 0)
+        self.check_bool(os.truncate, 0)
 
     @unittest.skipUnless(hasattr(os, 'lseek'), 'test needs os.lseek()')
     def test_lseek(self):

Lib/test/test_posix.py

@@ -1514,6 +1514,13 @@ class TestPosixDirFd(unittest.TestCase):
             self.assertRaises(OverflowError,
                     posix.stat, name, dir_fd=10**20)
 
+            for fd in False, True:
+                with self.assertWarnsRegex(RuntimeWarning,
+                        'bool is used as a file descriptor') as cm:
+                    with self.assertRaises(OSError):
+                        posix.stat('nonexisting', dir_fd=fd)
+                self.assertEqual(cm.filename, __file__)
+
     @unittest.skipUnless(os.utime in os.supports_dir_fd, "test needs dir_fd support in os.utime()")
     def test_utime_dir_fd(self):
         with self.prepare_file() as (dir_fd, name, fullname):

Misc/NEWS.d/next/Library/2023-10-24-19-19-54.gh-issue-82626._hfLRf.rst

@@ -0,0 +1,2 @@
+Many functions now emit a warning if a boolean value is passed as a file
+descriptor argument.

Modules/_io/fileio.c

@@ -269,6 +269,13 @@ _io_FileIO___init___impl(fileio *self, PyObject *nameobj, const char *mode,
             self->fd = -1;
     }
 
+    if (PyBool_Check(nameobj)) {
+        if (PyErr_WarnEx(PyExc_RuntimeWarning,
+                "bool is used as a file descriptor", 1))
+        {
+            return -1;
+        }
+    }
     fd = PyLong_AsInt(nameobj);
     if (fd < 0) {
         if (!PyErr_Occurred()) {

Modules/faulthandler.c

@@ -119,6 +119,13 @@ faulthandler_get_fileno(PyObject **file_ptr)
         }
     }
     else if (PyLong_Check(file)) {
+        if (PyBool_Check(file)) {
+            if (PyErr_WarnEx(PyExc_RuntimeWarning,
+                    "bool is used as a file descriptor", 1))
+            {
+                return -1;
+            }
+        }
         fd = PyLong_AsInt(file);
         if (fd == -1 && PyErr_Occurred())
             return -1;

Modules/posixmodule.c

@@ -969,6 +969,13 @@ _fd_converter(PyObject *o, int *p)
     int overflow;
     long long_value;
 
+    if (PyBool_Check(o)) {
+        if (PyErr_WarnEx(PyExc_RuntimeWarning,
+                "bool is used as a file descriptor", 1))
+        {
+            return 0;
+        }
+    }
     PyObject *index = _PyNumber_Index(o);
     if (index == NULL) {
         return 0;

Objects/fileobject.c

@@ -174,6 +174,13 @@ PyObject_AsFileDescriptor(PyObject *o)
     PyObject *meth;
 
     if (PyLong_Check(o)) {
+        if (PyBool_Check(o)) {
+            if (PyErr_WarnEx(PyExc_RuntimeWarning,
+                    "bool is used as a file descriptor", 1))
+            {
+                return -1;
+            }
+        }
         fd = PyLong_AsInt(o);
     }
     else if (PyObject_GetOptionalAttr(o, &_Py_ID(fileno), &meth) < 0) {