What’s new in Python 3.15

Editor:

TBD

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

For full details, see the changelog.

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.15 moves towards release, so it’s worth checking back even after reading earlier versions.

Summary — release highlights

New features

Other language changes

• Several error messages incorrectly using the term “argument” have been corrected. (Contributed by Stan Ulbrych in gh-133382.)

New modules

• None yet.

Improved modules

dbm

• Added new reorganize() methods to dbm.dumb and 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 dbm.gnu.open() which allows to disable the use of mmap(2). This may harm performance, but improve crash tolerance. (Contributed by Serhiy Storchaka in gh-66234.)

difflib

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

math

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

os.path

• The strict parameter to os.path.realpath() accepts a new value, os.path.ALLOW_MISSING. If used, errors other than 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.)

re

• Add the compile_template() method for the pattern object which allows to pre-compile replacement strings. (Contributed by Serhiy Storchaka in gh-105636.)

shelve

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

sqlite3

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

ssl

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

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.)

• 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.)

• extract() and 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, LinkFallbackError. (Contributed by Petr Viktorin for CVE 2025-4330 and CVE 2024-12718.)

• extract() and extractall() no longer extract rejected members when errorlevel() is zero. (Contributed by Matt Prodani and Petr Viktorin in gh-112887 and CVE 2025-4435.)

zlib

• Allow combining two Adler-32 checksums via adler32_combine(). (Contributed by Callum Attryde and Bénédikt Tran in gh-134635.)

• Allow combining two CRC-32 checksums via crc32_combine(). (Contributed by Bénédikt Tran in gh-134635.)

Optimizations

module_name

• TODO

Deprecated

hashlib

• In hash function constructors such as new() or the direct hash-named constructors such as md5() and sha256(), their optional initial data parameter could also be passed a keyword argument named data= or string= in various 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

ctypes

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

http.server

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

platform

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

sysconfig

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

threading

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

typing

• The undocumented keyword argument syntax for creating 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 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.)

wave

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

Porting to Python 3.15

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

Build changes

C API changes

New features

• Add PySys_GetAttr(), PySys_GetAttrString(), PySys_GetOptionalAttr(), and PySys_GetOptionalAttrString() functions as replacements for PySys_GetObject(). (Contributed by Serhiy Storchaka in gh-108512.)

• Add 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)

Porting to Python 3.15

• sqlite3.Connection APIs has been cleaned up.

  • All parameters of sqlite3.connect() except database are now keyword-only.

  • The first three parameters of methods create_function() and create_aggregate() are now positional-only.

  • The first parameter of methods set_authorizer(), set_progress_handler() and set_trace_callback() is now positional-only.

  (Contributed by Serhiy Storchaka in gh-133595.)

Deprecated C APIs

• TODO

Removed C APIs

• Remove deprecated PyUnicode functions:

  • PyUnicode_AsDecodedObject(): Use PyCodec_Decode() instead.

  • PyUnicode_AsDecodedUnicode(): Use PyCodec_Decode() instead; Note that some codecs (for example, “base64”) may return a type other than str, such as bytes.

  • PyUnicode_AsEncodedObject(): Use PyCodec_Encode() instead.

  • PyUnicode_AsEncodedUnicode(): Use PyCodec_Encode() instead; Note that some codecs (for example, “base64”) may return a type other than bytes, such as str.

  (Contributed by Stan Ulbrych in gh-133612)

• PyImport_ImportModuleNoBlock(): deprecated alias of PyImport_ImportModule(). (Contributed by Bénédikt Tran in gh-133644.)

The following functions are removed in favor of PyConfig_Get(). The pythoncapi-compat project can be used to get PyConfig_Get() on Python 3.13 and older.

• Python initialization functions:

  • Py_GetExecPrefix(): use PyConfig_Get("base_exec_prefix") (sys.base_exec_prefix) instead. Use PyConfig_Get("exec_prefix") (sys.exec_prefix) if virtual environments need to be handled.

  • Py_GetPath(): use PyConfig_Get("module_search_paths") (sys.path) instead.

  • Py_GetPrefix(): use PyConfig_Get("base_prefix") (sys.base_prefix) instead. Use PyConfig_Get("prefix") (sys.prefix) if virtual environments need to be handled.

  • Py_GetProgramFullPath(): use PyConfig_Get("executable") (sys.executable) instead.

  • Py_GetProgramName(): use PyConfig_Get("executable") (sys.executable) instead.

  • Py_GetPythonHome(): use PyConfig_Get("home") or the PYTHONHOME environment variable instead.

  (Contributed by Bénédikt Tran in gh-133644.)