May 21, 2025 · May 21, 2025
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
        if closed:
            return

        if dealloc_warn := getattr(self, "_dealloc_warn", None):
            dealloc_warn(self)

        # If close() fails, the caller logs the exception with
        # sys.unraisablehook. close() must be called at the end at __del__().
        self.close()
        else:
            return "<{}.{} name={!r}>".format(modname, clsname, name)

    def _dealloc_warn(self, source):
        if dealloc_warn := getattr(self.raw, "_dealloc_warn", None):
            dealloc_warn(source)

    ### Lower-level APIs ###

    def fileno(self):
            raise
        self._fd = fd

    def__del__(self):
    def_dealloc_warn(self, source):
        if self._fd >= 0 and self._closefd and not self.closed:
            import warnings
            warnings.warn('unclosed file%r' % (self,), ResourceWarning,
            warnings.warn(f'unclosed file{source!r}', ResourceWarning,
                          stacklevel=2, source=self)
            self.close()

    def __getstate__(self):
        raise TypeError(f"cannot pickle {self.__class__.__name__!r} object")
        if not self.closed:
            self._stat_atopen = None
            try:
                if self._closefd:
                if self._closefd and self._fd >= 0:
                    os.close(self._fd)
            finally:
                super().close()
    def newlines(self):
        return self._decoder.newlines if self._decoder else None

    def _dealloc_warn(self, source):
        if dealloc_warn := getattr(self.buffer, "_dealloc_warn", None):
            dealloc_warn(source)


 class StringIO(TextIOWrapper):
    """Text I/O implementation using an in-memory buffer.
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
        self._check_abc_inheritance(io)

    def _check_warn_on_dealloc(self, *args, **kwargs):
        f = open(*args, **kwargs)
        f =self.open(*args, **kwargs)
        r = repr(f)
        with self.assertWarns(ResourceWarning) as cm:
            f = None
        r, w = os.pipe()
        fds += r, w
        with warnings_helper.check_no_resource_warning(self):
            open(r, *args, closefd=False, **kwargs)
 self.open(r, *args, closefd=False, **kwargs)

    @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
    def test_warn_on_dealloc_fd(self):
diff --git a/Misc/NEWS.d/next/Library/2025-05-17-20-23-57.gh-issue-133982.smS7au.rst b/Misc/NEWS.d/next/Library/2025-05-17-20-23-57.gh-issue-133982.smS7au.rst
 Emit :exc:`RuntimeWarning` in the Python implementation of :mod:`io` when
 the :term:`file-like object <file object>` is not closed explicitly in the
 presence of multiple I/O layers.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -407,6 +407,9 @@ def __del__(self):
		if closed:
		return

		if dealloc_warn := getattr(self, "_dealloc_warn", None):
		dealloc_warn(self)

		# If close() fails, the caller logs the exception with
		# sys.unraisablehook. close() must be called at the end at __del__().
		self.close()
Expand DownExpand Up		@@ -853,6 +856,10 @@ def __repr__(self):
		else:
		return "<{}.{} name={!r}>".format(modname, clsname, name)

		def _dealloc_warn(self, source):
		if dealloc_warn := getattr(self.raw, "_dealloc_warn", None):
		dealloc_warn(source)

		### Lower-level APIs ###

		def fileno(self):
Expand DownExpand Up		@@ -1600,12 +1607,11 @@ def __init__(self, file, mode='r', closefd=True, opener=None):
		raise
		self._fd = fd

		def__del__(self):
		def_dealloc_warn(self, source):
		if self._fd >= 0 and self._closefd and not self.closed:
		import warnings
		warnings.warn('unclosed file%r' % (self,), ResourceWarning,
		warnings.warn(f'unclosed file{source!r}', ResourceWarning,
		stacklevel=2, source=self)
		self.close()

		def __getstate__(self):
		raise TypeError(f"cannot pickle {self.__class__.__name__!r} object")
Expand DownExpand Up		@@ -1780,7 +1786,7 @@ def close(self):
		if not self.closed:
		self._stat_atopen = None
		try:
		if self._closefd:
		if self._closefd and self._fd >= 0:
		os.close(self._fd)
		finally:
		super().close()
Expand DownExpand Up		@@ -2689,6 +2695,10 @@ def readline(self, size=None):
		def newlines(self):
		return self._decoder.newlines if self._decoder else None

		def _dealloc_warn(self, source):
		if dealloc_warn := getattr(self.buffer, "_dealloc_warn", None):
		dealloc_warn(source)


		class StringIO(TextIOWrapper):
		"""Text I/O implementation using an in-memory buffer.
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -4417,7 +4417,7 @@ def test_abc_inheritance_official(self):
		self._check_abc_inheritance(io)

		def _check_warn_on_dealloc(self, args, *kwargs):
		f = open(args, *kwargs)
		f =self.open(args, *kwargs)
		r = repr(f)
		with self.assertWarns(ResourceWarning) as cm:
		f = None
Expand DownExpand Up		@@ -4446,7 +4446,7 @@ def cleanup_fds():
		r, w = os.pipe()
		fds += r, w
		with warnings_helper.check_no_resource_warning(self):
		open(r, args, closefd=False, *kwargs)
		self.open(r, args, closefd=False, *kwargs)

		@unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
		def test_warn_on_dealloc_fd(self):
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Emit :exc:`RuntimeWarning` in the Python implementation of :mod:`io` when
		the :term:`file-like object <file object>` is not closed explicitly in the
		presence of multiple I/O layers.