This article explains the new features in Python 3.15, compared to 3.14.

For full details, see the :ref:`changelog <changelog>`.

• Several error messages incorrectly using the term "argument" have been corrected. (Contributed by Stan Ulbrych in :gh:`133382`.)

• None yet.

• Added new :meth:`!reorganize` methods to :mod:`dbm.dumb` and :mod:`dbm.sqlite3` which allow to recover unused free space previously occupied by deleted entries. (Contributed by Andrea Oliveri in :gh:`134004`.)
• Add the 'm' flag for :func:`dbm.gnu.open` which allows to disable the use of :manpage:`mmap(2)`. This may harm performance, but improve crash tolerance. (Contributed by Serhiy Storchaka in :gh:`66234`.)

• Improved the styling of HTML diff pages generated by the :class:`difflib.HtmlDiff` class, and migrated the output to the HTML5 standard. (Contributed by Jiahao Li in :gh:`134580`.)

• Add :func:`math.isnormal` and :func:`math.issubnormal` functions. (Contributed by Sergey B Kirpichev in :gh:`132908`.)

• The strict parameter to :func:`os.path.realpath` accepts a new value, :data:`os.path.ALLOW_MISSING`. If used, errors other than :exc:`FileNotFoundError` will be re-raised; the resulting path can be missing but it will be free of symlinks. (Contributed by Petr Viktorin for :cve:`2025-4517`.)

• Added new :meth:`!reorganize` method to :mod:`shelve` used to recover unused free space previously occupied by deleted entries. (Contributed by Andrea Oliveri in :gh:`134004`.)

• Support SQL keyword completion in the :mod:`sqlite3` command-line interface. (Contributed by Long Tan in :gh:`133393`.)

• Indicate through :data:`ssl.HAS_PSK_TLS13` whether the :mod:`ssl` module supports "External PSKs" in TLSv1.3, as described in RFC 9258. (Contributed by Will Childs-Klein in :gh:`133624`.)

• :func:`~tarfile.data_filter` now normalizes symbolic link targets in order to avoid path traversal attacks. (Contributed by Petr Viktorin in :gh:`127987` and :cve:`2025-4138`.)
• :func:`~tarfile.TarFile.extractall` now skips fixing up directory attributes when a directory was removed or replaced by another kind of file. (Contributed by Petr Viktorin in :gh:`127987` and :cve:`2024-12718`.)
• :func:`~tarfile.TarFile.extract` and :func:`~tarfile.TarFile.extractall` now (re-)apply the extraction filter when substituting a link (hard or symbolic) with a copy of another archive member, and when fixing up directory attributes. The former raises a new exception, :exc:`~tarfile.LinkFallbackError`. (Contributed by Petr Viktorin for :cve:`2025-4330` and :cve:`2024-12718`.)
• :func:`~tarfile.TarFile.extract` and :func:`~tarfile.TarFile.extractall` no longer extract rejected members when :func:`~tarfile.TarFile.errorlevel` is zero. (Contributed by Matt Prodani and Petr Viktorin in :gh:`112887` and :cve:`2025-4435`.)

• Allow combining two Adler-32 checksums via :func:`~zlib.adler32_combine`. (Contributed by Callum Attryde and Bénédikt Tran in :gh:`134635`.)
• Allow combining two CRC-32 checksums via :func:`~zlib.crc32_combine`. (Contributed by Bénédikt Tran in :gh:`134635`.)

• TODO

• In hash function constructors such as :func:`~hashlib.new` or the direct hash-named constructors such as :func:`~hashlib.md5` and :func:`~hashlib.sha256`, their optional initial data parameter could also be passed a keyword argument named data= or string= in various :mod:`hashlib` implementations.

  Support for the string keyword argument name is now deprecated and is slated for removal in Python 3.19. Prefer passing the initial data as a positional argument for maximum backwards compatibility.

  (Contributed by Bénédikt Tran in :gh:`134978`.)

• Removed the undocumented function :func:`!ctypes.SetPointerType`, which has been deprecated since Python 3.13. (Contributed by Bénédikt Tran in :gh:`133866`.)

• Removed the :class:`!CGIHTTPRequestHandler` class and the --cgi flag from the :program:`python -m http.server` command-line interface. They were deprecated in Python 3.13. (Contributed by Bénédikt Tran in :gh:`133810`.)

• Removed the :func:`!platform.java_ver` function, which was deprecated since Python 3.13. (Contributed by Alexey Makridenko in :gh:`133604`.)

• Removed the check_home parameter of :func:`sysconfig.is_python_build`. (Contributed by Filipe Laíns in :gh:`92897`.)

• Remove support for arbitrary positional or keyword arguments in the C implementation of :class:`~threading.RLock` objects. This was deprecated in Python 3.14. (Contributed by Bénédikt Tran in :gh:`134087`.)

• The undocumented keyword argument syntax for creating :class:`~typing.NamedTuple` classes (for example, Point = NamedTuple("Point", x=int, y=int)) is no longer supported. Use the class-based syntax or the functional syntax instead. (Contributed by Bénédikt Tran in :gh:`133817`.)
• Using TD = TypedDict("TD") or TD = TypedDict("TD", None) to construct a :class:`~typing.TypedDict` type with zero field is no longer supported. Use class TD(TypedDict): pass or TD = TypedDict("TD", {}) instead. (Contributed by Bénédikt Tran in :gh:`133823`.)

• Removed the getmark(), setmark() and getmarkers() methods of the :class:`~wave.Wave_read` and :class:`~wave.Wave_write` classes, which were deprecated since Python 3.13. (Contributed by Bénédikt Tran in :gh:`133873`.)

This section lists previously described changes and other bugfixes that may require changes to your code.

• Add :c:func:`PySys_GetAttr`, :c:func:`PySys_GetAttrString`, :c:func:`PySys_GetOptionalAttr`, and :c:func:`PySys_GetOptionalAttrString` functions as replacements for :c:func:`PySys_GetObject`. (Contributed by Serhiy Storchaka in :gh:`108512`.)
• Add :c:type:`PyUnstable_Unicode_GET_CACHED_HASH` to get the cached hash of a string. See the documentation for caveats. (Contributed by Petr Viktorin in :gh:`131510`)

• :class:`sqlite3.Connection` APIs has been cleaned up.

  • All parameters of :func:`sqlite3.connect` except database are now keyword-only.
  • The first three parameters of methods :meth:`~sqlite3.Connection.create_function` and :meth:`~sqlite3.Connection.create_aggregate` are now positional-only.
  • The first parameter of methods :meth:`~sqlite3.Connection.set_authorizer`, :meth:`~sqlite3.Connection.set_progress_handler` and :meth:`~sqlite3.Connection.set_trace_callback` is now positional-only.

  (Contributed by Serhiy Storchaka in :gh:`133595`.)

• Private functions promoted to public C APIs:

  • PyMutex_IsLocked() : :c:func:`PyMutex_IsLocked`

  The pythoncapi-compat project can be used to get most of these new functions on Python 3.14 and older.

• TODO

• Remove deprecated PyUnicode functions:

  • :c:func:`!PyUnicode_AsDecodedObject`: Use :c:func:`PyCodec_Decode` instead.
  • :c:func:`!PyUnicode_AsDecodedUnicode`: Use :c:func:`PyCodec_Decode` instead; Note that some codecs (for example, "base64") may return a type other than :class:`str`, such as :class:`bytes`.
  • :c:func:`!PyUnicode_AsEncodedObject`: Use :c:func:`PyCodec_Encode` instead.
  • :c:func:`!PyUnicode_AsEncodedUnicode`: Use :c:func:`PyCodec_Encode` instead; Note that some codecs (for example, "base64") may return a type other than :class:`bytes`, such as :class:`str`.

  (Contributed by Stan Ulbrych in :gh:`133612`)

• :c:func:`!PyImport_ImportModuleNoBlock`: deprecated alias of :c:func:`PyImport_ImportModule`. (Contributed by Bénédikt Tran in :gh:`133644`.)

The following functions are removed in favor of :c:func:`PyConfig_Get`. The pythoncapi-compat project can be used to get :c:func:`!PyConfig_Get` on Python 3.13 and older.

• Python initialization functions:

  • :c:func:`!Py_GetExecPrefix`: use :c:func:`PyConfig_Get("base_exec_prefix") <PyConfig_Get>` (:data:`sys.base_exec_prefix`) instead. Use :c:func:`PyConfig_Get("exec_prefix") <PyConfig_Get>` (:data:`sys.exec_prefix`) if :ref:`virtual environments <venv-def>` need to be handled.
  • :c:func:`!Py_GetPath`: use :c:func:`PyConfig_Get("module_search_paths") <PyConfig_Get>` (:data:`sys.path`) instead.
  • :c:func:`!Py_GetPrefix`: use :c:func:`PyConfig_Get("base_prefix") <PyConfig_Get>` (:data:`sys.base_prefix`) instead. Use :c:func:`PyConfig_Get("prefix") <PyConfig_Get>` (:data:`sys.prefix`) if :ref:`virtual environments <venv-def>` need to be handled.
  • :c:func:`!Py_GetProgramFullPath`: use :c:func:`PyConfig_Get("executable") <PyConfig_Get>` (:data:`sys.executable`) instead.
  • :c:func:`!Py_GetProgramName`: use :c:func:`PyConfig_Get("executable") <PyConfig_Get>` (:data:`sys.executable`) instead.
  • :c:func:`!Py_GetPythonHome`: use :c:func:`PyConfig_Get("home") <PyConfig_Get>` or the :envvar:`PYTHONHOME` environment variable instead.

  (Contributed by Bénédikt Tran in :gh:`133644`.)