Configure Python

.. highlight:: sh

.. _build-requirements:

Build Requirements

To build CPython, you will need:

A C11 <https://en.cppreference.com/w/c/11>_ compiler. Optional C11 features <https://en.wikipedia.org/wiki/C11_(C_standard_revision)#Optional_features>_ are not required.
On Windows, Microsoft Visual Studio 2017 or later is required.
Support for IEEE 754 <https://en.wikipedia.org/wiki/IEEE_754>_ floating-point numbers and floating-point Not-a-Number (NaN) <https://en.wikipedia.org/wiki/NaN#Floating_point>_.
Support for threads.

.. versionchanged:: 3.5 On Windows, Visual Studio 2015 or later is now required.

.. versionchanged:: 3.6 Selected C99 features, like <stdint.h> and static inline functions, are now required.

.. versionchanged:: 3.7 Thread support is now required.

.. versionchanged:: 3.11 C11 compiler, IEEE 754 and NaN support are now required. On Windows, Visual Studio 2017 or later is required.

See also :pep:7 "Style Guide for C Code" and :pep:11 "CPython platform support".

.. _optional-module-requirements:

Requirements for optional modules

Some :term:optional modules <optional module> of the standard library require third-party libraries installed for development (for example, header files must be available).

Missing requirements are reported in the configure output. Modules that are missing due to missing dependencies are listed near the end of the make output, sometimes using an internal name, for example, _ctypes for :mod:ctypes module.

If you distribute a CPython interpreter without optional modules, it's best practice to advise users, who generally expect that standard library modules are available.

Dependencies to build optional modules are:

.. list-table:: :header-rows: 1 :align: left

- Dependency
- Minimum version
- Python module
- libbz2 <https://sourceware.org/bzip2/>_
- :mod:bz2
- libffi <https://sourceware.org/libffi/>_
- 3.3.0 recommended
- :mod:ctypes
- liblzma <https://tukaani.org/xz/>_
- :mod:lzma
- libmpdec <https://www.bytereef.org/mpdecimal/doc/libmpdec/>_
- 2.5.0
- :mod:decimal [1]_
- libreadline <https://tiswww.case.edu/php/chet/readline/rltop.html>_ or libedit <https://www.thrysoee.dk/editline/>_ [2]_
- :mod:readline
- libuuid <https://linux.die.net/man/3/libuuid>_
- _uuid [3]_
- ncurses <https://gnu.org/software/ncurses/ncurses.html>_ [4]_
- :mod:curses
- OpenSSL <https://openssl-library.org/>_
- | 3.0.18 recommended | (1.1.1 minimum)
- :mod:ssl, :mod:hashlib [5]_
- SQLite <https://sqlite.org/>_
- 3.15.2
- :mod:sqlite3
- Tcl/Tk <https://www.tcl-lang.org/>_
- 8.5.12
- :mod:tkinter, :ref:IDLE <idle>, :mod:turtle
- zlib <https://www.zlib.net>_
- 1.2.2.1
- :mod:zlib, :mod:gzip, :mod:ensurepip
- zstd <https://facebook.github.io/zstd/>_
- 1.4.5
- :mod:compression.zstd

.. [1] If libmpdec is not available, the :mod:decimal module will use a pure-Python implementation. See :option:--with-system-libmpdec for details. .. [2] See :option:--with-readline for choosing the backend for the :mod:readline module. .. [3] The :mod:uuid module uses _uuid to generate "safe" UUIDs. See the module documentation for details. .. [4] The :mod:curses module requires the libncurses or libncursesw library. The :mod:curses.panel module additionally requires the libpanel or libpanelw library. .. [5] If OpenSSL is not available, the :mod:hashlib module will use bundled implementations of several hash functions. See :option:--with-builtin-hashlib-hashes for forcing usage of OpenSSL.

Note that the table does not include all optional modules; in particular, platform-specific modules like :mod:winreg are not listed here.

.. seealso::

The devguide <https://devguide.python.org/getting-started/setup-building/#install-dependencies>_ includes a full list of dependencies required to build all modules and instructions on how to install them on common platforms.
:option:--with-system-expat allows building with an external libexpat <https://libexpat.github.io/>_ library.
:ref:configure-options-for-dependencies

.. versionchanged:: 3.1 Tcl/Tk version 8.3.1 is now required for :mod:tkinter.

.. versionchanged:: 3.5 Tcl/Tk version 8.4 is now required for :mod:tkinter.

.. versionchanged:: 3.7 OpenSSL 1.0.2 is now required for :mod:hashlib and :mod:ssl.

.. versionchanged:: 3.10 OpenSSL 1.1.1 is now required for :mod:hashlib and :mod:ssl. SQLite 3.7.15 is now required for :mod:sqlite3.

.. versionchanged:: 3.11 Tcl/Tk version 8.5.12 is now required for :mod:tkinter.

.. versionchanged:: 3.13 SQLite 3.15.2 is now required for :mod:sqlite3.

Generated files

To reduce build dependencies, Python source code contains multiple generated files. Commands to regenerate all generated files::

make regen-all
make regen-stdlib-module-names
make regen-limited-abi
make regen-configure

The Makefile.pre.in file documents generated files, their inputs, and tools used to regenerate them. Search for regen-* make targets.

configure script

The make regen-configure command regenerates the aclocal.m4 file and the configure script using the Tools/build/regen-configure.sh shell script which uses an Ubuntu container to get the same tools versions and have a reproducible output.

The container is optional, the following command can be run locally::

autoreconf -ivf -Werror

The generated files can change depending on the exact versions of the tools used. The container that CPython uses has Autoconf <https://gnu.org/software/autoconf>_ 2.72, aclocal from Automake <https://www.gnu.org/software/automake>_ 1.16.5, and pkg-config <https://www.freedesktop.org/wiki/Software/pkg-config/>_ 1.8.1.

.. versionchanged:: 3.13 Autoconf 2.71 and aclocal 1.16.5 and are now used to regenerate :file:configure.

.. versionchanged:: 3.14 Autoconf 2.72 is now used to regenerate :file:configure.

.. _configure-options:

Configure Options

List all :file:configure script options using::

./configure --help

See also the :file:Misc/SpecialBuilds.txt in the Python source distribution.

General Options

.. option:: --enable-loadable-sqlite-extensions

Support loadable extensions in the :mod:!_sqlite extension module (default is no) of the :mod:sqlite3 module.

See the :meth:sqlite3.Connection.enable_load_extension method of the :mod:sqlite3 module.

.. versionadded:: 3.6

.. option:: --disable-ipv6

Disable IPv6 support (enabled by default if supported), see the :mod:socket module.

.. option:: --enable-big-digits=[15|30]

Define the size in bits of Python :class:int digits: 15 or 30 bits.

By default, the digit size is 30.

Define the PYLONG_BITS_IN_DIGIT to 15 or 30.

See :data:sys.int_info.bits_per_digit <sys.int_info>.

.. option:: --with-suffix=SUFFIX

Set the Python executable suffix to SUFFIX.

The default suffix is .exe on Windows and macOS (python.exe executable), .js on Emscripten node, .html on Emscripten browser, .wasm on WASI, and an empty string on other platforms (python executable).

.. versionchanged:: 3.11 The default suffix on WASM platform is one of .js, .html or .wasm.

.. option:: --with-tzpath=<list of absolute paths separated by pathsep>

Select the default time zone search path for :const:zoneinfo.TZPATH. See the :ref:Compile-time configuration <zoneinfo_data_compile_time_config> of the :mod:zoneinfo module.

Default: /usr/share/zoneinfo:/usr/lib/zoneinfo:/usr/share/lib/zoneinfo:/etc/zoneinfo.

See :data:os.pathsep path separator.

.. versionadded:: 3.9

.. option:: --without-decimal-contextvar

Build the _decimal extension module using a thread-local context rather than a coroutine-local context (default), see the :mod:decimal module.

See :const:decimal.HAVE_CONTEXTVAR and the :mod:contextvars module.

.. versionadded:: 3.9

.. option:: --with-dbmliborder=<list of backend names>

Override order to check db backends for the :mod:dbm module

A valid value is a colon (:) separated string with the backend names:

ndbm;
gdbm;
bdb.

.. option:: --without-c-locale-coercion

Disable C locale coercion to a UTF-8 based locale (enabled by default).

Don't define the PY_COERCE_C_LOCALE macro.

See :envvar:PYTHONCOERCECLOCALE and the :pep:538.

.. option:: --with-platlibdir=DIRNAME

Python library directory name (default is lib).

Fedora and SuSE use lib64 on 64-bit platforms.

See :data:sys.platlibdir.

.. versionadded:: 3.9

.. option:: --with-wheel-pkg-dir=PATH

Directory of wheel packages used by the :mod:ensurepip module (none by default).

Some Linux distribution packaging policies recommend against bundling dependencies. For example, Fedora installs wheel packages in the /usr/share/python-wheels/ directory and don't install the :mod:!ensurepip._bundled package.

.. versionadded:: 3.10

.. option:: --with-pkg-config=[check|yes|no]

Whether configure should use :program:pkg-config to detect build dependencies.

check (default): :program:pkg-config is optional
yes: :program:pkg-config is mandatory
no: configure does not use :program:pkg-config even when present

.. versionadded:: 3.11

.. option:: --with-missing-stdlib-config=FILE

Path to a JSON <https://www.json.org/json-en.html>_ configuration file containing custom error messages for missing :term:standard library modules.

This option is intended for Python distributors who wish to provide distribution-specific guidance when users encounter standard library modules that are missing or packaged separately.

The JSON file should map missing module names to custom error message strings. For example, if your distribution packages :mod:tkinter and :mod:_tkinter separately and excludes :mod:!_gdbm for legal reasons, the configuration could contain:

.. code-block:: json

  {
      "_gdbm": "The '_gdbm' module is not available in this distribution",
      "tkinter": "Install the python-tk package to use tkinter",
      "_tkinter": "Install the python-tk package to use tkinter",
  }

.. versionadded:: 3.15

.. option:: --enable-pystats

Turn on internal Python performance statistics gathering.

By default, statistics gathering is off. Use python3 -X pystats command or set PYTHONSTATS=1 environment variable to turn on statistics gathering at Python startup.

At Python exit, dump statistics if statistics gathering was on and not cleared.

Effects:

Add :option:-X pystats <-X> command line option.
Add :envvar:!PYTHONSTATS environment variable.
Define the Py_STATS macro.
Add functions to the :mod:sys module:
- :func:!sys._stats_on: Turns on statistics gathering.
- :func:!sys._stats_off: Turns off statistics gathering.
- :func:!sys._stats_clear: Clears the statistics.
- :func:!sys._stats_dump: Dump statistics to file, and clears the statistics.

The statistics will be dumped to a arbitrary (probably unique) file in /tmp/py_stats/ (Unix) or C:\temp\py_stats\ (Windows). If that directory does not exist, results will be printed on stderr.

Use Tools/scripts/summarize_stats.py to read the stats.

Statistics:

Opcode:
- Specialization: success, failure, hit, deferred, miss, deopt, failures;
- Execution count;
- Pair count.
Call:
- Inlined Python calls;
- PyEval calls;
- Frames pushed;
- Frame object created;
- Eval calls: vector, generator, legacy, function VECTORCALL, build class, slot, function "ex", API, method.
Object:
- incref and decref;
- interpreter incref and decref;
- allocations: all, 512 bytes, 4 kiB, big;
- free;
- to/from free lists;
- dictionary materialized/dematerialized;
- type cache;
- optimization attempts;
- optimization traces created/executed;
- uops executed.
Garbage collector:
- Garbage collections;
- Objects visited;
- Objects collected.

.. versionadded:: 3.11

.. _free-threading-build:

.. option:: --disable-gil

.. c:macro:: Py_GIL_DISABLED :no-typesetting:

Enables support for running Python without the :term:global interpreter lock (GIL): :term:free-threaded build.

Defines the Py_GIL_DISABLED macro and adds "t" to :data:sys.abiflags.

See :ref:whatsnew313-free-threaded-cpython for more detail.

.. versionadded:: 3.13

.. option:: --enable-experimental-jit=[no|yes|yes-off|interpreter]

Indicate how to integrate the :ref:experimental just-in-time compiler <whatsnew314-jit-compiler>.

no: Don't build the JIT.
yes: Enable the JIT. To disable it at runtime, set the environment variable :envvar:PYTHON_JIT=0 <PYTHON_JIT>.
yes-off: Build the JIT, but disable it by default. To enable it at runtime, set the environment variable :envvar:PYTHON_JIT=1 <PYTHON_JIT>.
interpreter: Enable the "JIT interpreter" (only useful for those debugging the JIT itself). To disable it at runtime, set the environment variable :envvar:PYTHON_JIT=0 <PYTHON_JIT>.

--enable-experimental-jit=no is the default behavior if the option is not provided, and --enable-experimental-jit is shorthand for --enable-experimental-jit=yes. See :file:Tools/jit/README.md for more information, including how to install the necessary build-time dependencies.

.. note::

  When building CPython with JIT enabled, ensure that your system has Python 3.11 or later installed.

.. versionadded:: 3.13

.. option:: PKG_CONFIG

Path to pkg-config utility.

.. option:: PKG_CONFIG_LIBDIR .. option:: PKG_CONFIG_PATH

pkg-config options.

.. option:: --disable-epoll

Build without epoll, meaning that :py:func:select.epoll will not be present even if the system provides an :manpage:epoll_create <epoll_create(2)> function. This may be used on systems where :manpage:!epoll_create or :manpage:epoll_create1 <epoll_create1(2)> is available but incompatible with Linux semantics.

.. versionadded:: 3.15

C compiler options

.. option:: CC

C compiler command.

.. option:: CFLAGS

C compiler flags.

.. option:: CPP

C preprocessor command.

.. option:: CPPFLAGS

C preprocessor flags, e.g. :samp:-I{include_dir}.

Linker options

.. option:: LDFLAGS

Linker flags, e.g. :samp:-L{library_directory}.

.. option:: LIBS

Libraries to pass to the linker, e.g. :samp:-l{library}.

.. option:: MACHDEP

Name for machine-dependent library files.

.. _configure-options-for-dependencies:

Options for third-party dependencies

.. versionadded:: 3.11

.. option:: BZIP2_CFLAGS .. option:: BZIP2_LIBS

C compiler and linker flags to link Python to libbz2, used by :mod:bz2 module, overriding pkg-config.

.. option:: CURSES_CFLAGS .. option:: CURSES_LIBS

C compiler and linker flags for libncurses or libncursesw, used by :mod:curses module, overriding pkg-config.

.. option:: GDBM_CFLAGS .. option:: GDBM_LIBS

C compiler and linker flags for gdbm.

.. option:: LIBEDIT_CFLAGS .. option:: LIBEDIT_LIBS

C compiler and linker flags for libedit, used by :mod:readline module, overriding pkg-config.

.. option:: LIBFFI_CFLAGS .. option:: LIBFFI_LIBS

C compiler and linker flags for libffi, used by :mod:ctypes module, overriding pkg-config.

.. option:: LIBMPDEC_CFLAGS .. option:: LIBMPDEC_LIBS

C compiler and linker flags for libmpdec, used by :mod:decimal module, overriding pkg-config.

.. note::

  These environment variables have no effect unless
  :option:`--with-system-libmpdec` is specified.

.. option:: LIBLZMA_CFLAGS .. option:: LIBLZMA_LIBS

C compiler and linker flags for liblzma, used by :mod:lzma module, overriding pkg-config.

.. option:: LIBREADLINE_CFLAGS .. option:: LIBREADLINE_LIBS

C compiler and linker flags for libreadline, used by :mod:readline module, overriding pkg-config.

.. option:: LIBSQLITE3_CFLAGS .. option:: LIBSQLITE3_LIBS

C compiler and linker flags for libsqlite3, used by :mod:sqlite3 module, overriding pkg-config.

.. option:: LIBUUID_CFLAGS .. option:: LIBUUID_LIBS

C compiler and linker flags for libuuid, used by :mod:uuid module, overriding pkg-config.

.. option:: LIBZSTD_CFLAGS .. option:: LIBZSTD_LIBS

C compiler and linker flags for libzstd, used by :mod:compression.zstd module, overriding pkg-config.

.. versionadded:: 3.14

.. option:: PANEL_CFLAGS .. option:: PANEL_LIBS

C compiler and linker flags for PANEL, overriding pkg-config.

C compiler and linker flags for libpanel or libpanelw, used by :mod:curses.panel module, overriding pkg-config.

.. option:: TCLTK_CFLAGS .. option:: TCLTK_LIBS

C compiler and linker flags for TCLTK, overriding pkg-config.

.. option:: ZLIB_CFLAGS .. option:: ZLIB_LIBS

C compiler and linker flags for libzlib, used by :mod:gzip module, overriding pkg-config.

WebAssembly Options

.. option:: --enable-wasm-dynamic-linking

Turn on dynamic linking support for WASM.

Dynamic linking enables dlopen. File size of the executable increases due to limited dead code elimination and additional features.

.. versionadded:: 3.11

.. option:: --enable-wasm-pthreads

Turn on pthreads support for WASM.

.. versionadded:: 3.11

Install Options

.. option:: --prefix=PREFIX

Install architecture-independent files in PREFIX. On Unix, it defaults to :file:/usr/local.

This value can be retrieved at runtime using :data:sys.prefix.

As an example, one can use --prefix="$HOME/.local/" to install a Python in its home directory.

.. option:: --exec-prefix=EPREFIX

Install architecture-dependent files in EPREFIX, defaults to :option:--prefix.

This value can be retrieved at runtime using :data:sys.exec_prefix.

.. option:: --disable-test-modules

Don't build nor install test modules, like the :mod:test package or the :mod:!_testcapi extension module (built and installed by default).

.. versionadded:: 3.10

.. option:: --with-ensurepip=[upgrade|install|no]

Select the :mod:ensurepip command run on Python installation:

upgrade (default): run python -m ensurepip --altinstall --upgrade command.
install: run python -m ensurepip --altinstall command;
no: don't run ensurepip;

.. versionadded:: 3.6

Performance options

Configuring Python using --enable-optimizations --with-lto (PGO + LTO) is recommended for best performance. The experimental --enable-bolt flag can also be used to improve performance.

.. option:: --enable-optimizations

Enable Profile Guided Optimization (PGO) using :envvar:PROFILE_TASK (disabled by default).

The C compiler Clang requires llvm-profdata program for PGO. On macOS, GCC also requires it: GCC is just an alias to Clang on macOS.

Disable also semantic interposition in libpython if --enable-shared and GCC is used: add -fno-semantic-interposition to the compiler and linker flags.

.. note::

  During the build, you may encounter compiler warnings about
  profile data not being available for some source files.
  These warnings are harmless, as only a subset of the code is exercised
  during profile data acquisition.
  To disable these warnings on Clang, manually suppress them by adding
  ``-Wno-profile-instr-unprofiled`` to :envvar:`CFLAGS`.

.. versionadded:: 3.6

.. versionchanged:: 3.10 Use -fno-semantic-interposition on GCC.

.. envvar:: PROFILE_TASK

Environment variable used in the Makefile: Python command line arguments for the PGO generation task.

Default: -m test --pgo --timeout=$(TESTTIMEOUT).

.. versionadded:: 3.8

.. versionchanged:: 3.13 Task failure is no longer ignored silently.

.. option:: --with-lto=[full|thin|no|yes]

Enable Link Time Optimization (LTO) in any build (disabled by default).

The C compiler Clang requires llvm-ar for LTO (ar on macOS), as well as an LTO-aware linker (ld.gold or lld).

.. versionadded:: 3.6

.. versionadded:: 3.11 To use ThinLTO feature, use --with-lto=thin on Clang.

.. versionchanged:: 3.12 Use ThinLTO as the default optimization policy on Clang if the compiler accepts the flag.

.. option:: --enable-bolt

Enable usage of the BOLT post-link binary optimizer <https://github.com/llvm/llvm-project/tree/main/bolt>_ (disabled by default).

BOLT is part of the LLVM project but is not always included in their binary distributions. This flag requires that llvm-bolt and merge-fdata are available.

BOLT is still a fairly new project so this flag should be considered experimental for now. Because this tool operates on machine code its success is dependent on a combination of the build environment + the other optimization configure args + the CPU architecture, and not all combinations are supported. BOLT versions before LLVM 16 are known to crash BOLT under some scenarios. Use of LLVM 16 or newer for BOLT optimization is strongly encouraged.

The :envvar:!BOLT_INSTRUMENT_FLAGS and :envvar:!BOLT_APPLY_FLAGS :program:configure variables can be defined to override the default set of arguments for :program:llvm-bolt to instrument and apply BOLT data to binaries, respectively.

.. versionadded:: 3.12

.. option:: BOLT_APPLY_FLAGS

Arguments to llvm-bolt when creating a BOLT optimized binary <https://github.com/facebookarchive/BOLT>_.

.. versionadded:: 3.12

.. option:: BOLT_INSTRUMENT_FLAGS

Arguments to llvm-bolt when instrumenting binaries.

.. versionadded:: 3.12

.. option:: --with-computed-gotos

Enable computed gotos in evaluation loop (enabled by default on supported compilers).

.. option:: --with-tail-call-interp

Enable interpreters using tail calls in CPython. If enabled, enabling PGO (:option:--enable-optimizations) is highly recommended. This option specifically requires a C compiler with proper tail call support, and the preserve_none <https://clang.llvm.org/docs/AttributeReference.html#preserve-none>_ calling convention. For example, Clang 19 and newer supports this feature.

.. versionadded:: 3.14

.. option:: --without-mimalloc

Disable the fast :ref:mimalloc <mimalloc> allocator (enabled by default).

This option cannot be used together with :option:--disable-gil because the :term:free-threaded <free threading> build requires mimalloc.

See also :envvar:PYTHONMALLOC environment variable.

.. option:: --without-pymalloc

Disable the specialized Python memory allocator :ref:pymalloc <pymalloc> (enabled by default).

See also :envvar:PYTHONMALLOC environment variable.

.. option:: --with-pymalloc-hugepages

Enable huge page support for :ref:pymalloc <pymalloc> arenas (disabled by default). When enabled, the arena size on 64-bit platforms is increased to 2 MiB and arena allocation uses MAP_HUGETLB (Linux) or MEM_LARGE_PAGES (Windows) with automatic fallback to regular pages.

Even when compiled with this option, huge pages are not used at runtime unless the :envvar:PYTHON_PYMALLOC_HUGEPAGES environment variable is set to 1. This opt-in is required because huge pages

carry risks on Linux: if the huge-page pool is exhausted, page faults (including copy-on-write faults after :func:os.fork) deliver SIGBUS and kill the process.
need a special privilege on Windows. See the Windows documentation for large pages <https://learn.microsoft.com/windows/win32/memory/large-page-support>_ for details. Python will fail on startup if the required privilege SeLockMemoryPrivilege <https://learn.microsoft.com/previous-versions/windows/it-pro/windows-10/security/threat-protection/security-policy-settings/lock-pages-in-memory>_ is not held by the user.

The configure script checks that the platform supports MAP_HUGETLB and emits a warning if it is not available.

On Windows, use the --pymalloc-hugepages flag with build.bat or set the UsePymallocHugepages MSBuild property.

.. versionadded:: 3.15

.. option:: --without-doc-strings

Disable static documentation strings to reduce the memory footprint (enabled by default). Documentation strings defined in Python are not affected.

Don't define the WITH_DOC_STRINGS macro.

See the PyDoc_STRVAR() macro.

.. option:: --enable-profiling

Enable C-level code profiling with gprof (disabled by default).

.. option:: --with-strict-overflow

Add -fstrict-overflow to the C compiler flags (by default we add -fno-strict-overflow instead).

.. option:: --without-remote-debug

Deactivate remote debugging support described in :pep:768 (enabled by default). When this flag is provided the code that allows the interpreter to schedule the execution of a Python file in a separate process as described in :pep:768 is not compiled. This includes both the functionality to schedule code to be executed and the functionality to receive code to be executed.

.. c:macro:: Py_REMOTE_DEBUG

  This macro is defined by default, unless Python is configured with
  :option:`--without-remote-debug`.

  Note that even if the macro is defined, remote debugging may not be
  available (for example, on an incompatible platform).

.. versionadded:: 3.14

.. _debug-build:

Python Debug Build

A debug build is Python built with the :option:--with-pydebug configure option.

Effects of a debug build:

Display all warnings by default: the list of default warning filters is empty in the :mod:warnings module.
Add d to :data:sys.abiflags.
Add :func:!sys.gettotalrefcount function.
Add :option:-X showrefcount <-X> command line option.
Add :option:-d command line option and :envvar:PYTHONDEBUG environment variable to debug the parser.
Add support for the __lltrace__ variable: enable low-level tracing in the bytecode evaluation loop if the variable is defined.
Install :ref:debug hooks on memory allocators <default-memory-allocators> to detect buffer overflow and other memory errors.
Define Py_DEBUG and Py_REF_DEBUG macros.
Add runtime checks: code surrounded by #ifdef Py_DEBUG and #endif. Enable assert(...) and _PyObject_ASSERT(...) assertions: don't set the NDEBUG macro (see also the :option:--with-assertions configure option). Main runtime checks:
- Add sanity checks on the function arguments.
- Unicode and int objects are created with their memory filled with a pattern to detect usage of uninitialized objects.
- Ensure that functions which can clear or replace the current exception are not called with an exception raised.
- Check that deallocator functions don't change the current exception.
- The garbage collector (:func:gc.collect function) runs some basic checks on objects consistency.
- The :c:macro:!Py_SAFE_DOWNCAST() macro checks for integer underflow and overflow when downcasting from wide types to narrow types.

See also the :ref:Python Development Mode <devmode> and the :option:--with-trace-refs configure option.

.. versionchanged:: 3.8 Release builds are now ABI compatible with debug builds: defining the Py_DEBUG macro no longer implies the Py_TRACE_REFS macro (see the :option:--with-trace-refs option). However, debug builds still expose more symbols than release builds and code built against a debug build is not necessarily compatible with a release build.

Debug options

.. option:: --with-pydebug

:ref:Build Python in debug mode <debug-build>: define the Py_DEBUG macro (disabled by default).

.. option:: --with-trace-refs

Enable tracing references for debugging purpose (disabled by default).

Effects:

Define the Py_TRACE_REFS macro.
Add :func:sys.getobjects function.
Add :envvar:PYTHONDUMPREFS environment variable.

The :envvar:PYTHONDUMPREFS environment variable can be used to dump objects and reference counts still alive at Python exit.

:ref:Statically allocated objects <static-types> are not traced.

.. versionadded:: 3.8

.. versionchanged:: 3.13 This build is now ABI compatible with release build and :ref:debug build <debug-build>.

.. option:: --with-assertions

Build with C assertions enabled (default is no): assert(...); and _PyObject_ASSERT(...);.

If set, the NDEBUG macro is not defined in the :envvar:OPT compiler variable.

See also the :option:--with-pydebug option (:ref:debug build <debug-build>) which also enables assertions.

.. versionadded:: 3.6

.. option:: --with-valgrind

Enable Valgrind support (default is no).

.. option:: --with-dtrace

Enable DTrace support (default is no).

See :ref:Instrumenting CPython with DTrace and SystemTap <instrumentation>.

.. versionadded:: 3.6

.. option:: --with-address-sanitizer

Enable AddressSanitizer memory error detector, asan (default is no). To improve ASan detection capabilities you may also want to combine this with :option:--without-pymalloc to disable the specialized small-object allocator whose allocations are not tracked by ASan.

.. versionadded:: 3.6

.. option:: --with-memory-sanitizer

Enable MemorySanitizer allocation error detector, msan (default is no).

.. versionadded:: 3.6

.. option:: --with-undefined-behavior-sanitizer

Enable UndefinedBehaviorSanitizer undefined behaviour detector, ubsan (default is no).

.. versionadded:: 3.6

.. option:: --with-thread-sanitizer

Enable ThreadSanitizer data race detector, tsan (default is no).

.. versionadded:: 3.13

Linker options

.. option:: --enable-shared

Enable building a shared Python library: libpython (default is no).

.. option:: --without-static-libpython

Do not build libpythonMAJOR.MINOR.a and do not install python.o (built and enabled by default).

.. versionadded:: 3.10

Libraries options

.. option:: --with-libs='lib1 ...'

Link against additional libraries (default is no).

.. option:: --with-system-expat

Build the :mod:!pyexpat module using an installed expat library (default is no).

.. option:: --with-system-libmpdec

Build the _decimal extension module using an installed mpdecimal library, see the :mod:decimal module (default is yes).

.. versionadded:: 3.3

.. versionchanged:: 3.13 Default to using the installed mpdecimal library.

.. versionchanged:: 3.15

  A bundled copy of the library will no longer be selected
  implicitly if an installed ``mpdecimal`` library is not found.
  In Python 3.15 only, it can still be selected explicitly using
  ``--with-system-libmpdec=no`` or ``--without-system-libmpdec``.

.. deprecated-removed:: 3.13 3.16 A copy of the mpdecimal library sources will no longer be distributed with Python 3.16.

.. seealso:: :option:LIBMPDEC_CFLAGS and :option:LIBMPDEC_LIBS.

.. option:: --with-readline=readline|editline

Designate a backend library for the :mod:readline module.

readline: Use readline as the backend.
editline: Use editline as the backend.

.. versionadded:: 3.10

.. option:: --without-readline

Don't build the :mod:readline module (built by default).

Don't define the HAVE_LIBREADLINE macro.

.. versionadded:: 3.10

.. option:: --with-libm=STRING

Override libm math library to STRING (default is system-dependent).

.. option:: --with-libc=STRING

Override libc C library to STRING (default is system-dependent).

.. option:: --with-openssl=DIR

Root of the OpenSSL directory.

.. versionadded:: 3.7

.. option:: --with-openssl-rpath=[no|auto|DIR]

Set runtime library directory (rpath) for OpenSSL libraries:

no (default): don't set rpath;
auto: auto-detect rpath from :option:--with-openssl and pkg-config;
DIR: set an explicit rpath.

.. versionadded:: 3.10

Security Options

.. option:: --with-hash-algorithm=[fnv|siphash13|siphash24]

Select hash algorithm for use in Python/pyhash.c:

siphash13 (default);
siphash24;
fnv.

.. versionadded:: 3.4

.. versionadded:: 3.11 siphash13 is added and it is the new default.

.. option:: --with-builtin-hashlib-hashes=md5,sha1,sha256,sha512,sha3,blake2

Built-in hash modules:

md5;
sha1;
sha256;
sha512;
sha3 (with shake);
blake2.

.. versionadded:: 3.9

.. option:: --with-ssl-default-suites=[python|openssl|STRING]

Override the OpenSSL default cipher suites string:

python (default): use Python's preferred selection;
openssl: leave OpenSSL's defaults untouched;
STRING: use a custom string

See the :mod:ssl module.

.. versionadded:: 3.7

.. versionchanged:: 3.10

  The settings ``python`` and *STRING* also set TLS 1.2 as minimum
  protocol version.

.. option:: --disable-safety

Disable compiler options that are recommended by OpenSSF_ for security reasons with no performance overhead. If this option is not enabled, CPython will be built based on safety compiler options with no slow down. When this option is enabled, CPython will not be built with the compiler options listed below.

The following compiler options are disabled with :option:!--disable-safety:

-fstack-protector-strong_: Enable run-time checks for stack-based buffer overflows.
-Wtrampolines_: Enable warnings about trampolines that require executable stacks.

.. versionadded:: 3.14

.. option:: --enable-slower-safety

Enable compiler options that are recommended by OpenSSF_ for security reasons which require overhead. If this option is not enabled, CPython will not be built based on safety compiler options which performance impact. When this option is enabled, CPython will be built with the compiler options listed below.

The following compiler options are enabled with :option:!--enable-slower-safety:

-D_FORTIFY_SOURCE=3_: Fortify sources with compile- and run-time checks for unsafe libc usage and buffer overflows.

.. _-D_FORTIFY_SOURCE=3: https://github.com/ossf/wg-best-practices-os-developers/blob/main/docs/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.md#fortify-sources-for-unsafe-libc-usage-and-buffer-overflows

.. versionadded:: 3.14

macOS Options

See :source:Mac/README.rst.

.. option:: --enable-universalsdk .. option:: --enable-universalsdk=SDKDIR

Create a universal binary build. SDKDIR specifies which macOS SDK should be used to perform the build (default is no).

.. option:: --enable-framework .. option:: --enable-framework=INSTALLDIR

Create a Python.framework rather than a traditional Unix install. Optional INSTALLDIR specifies the installation path (default is no).

.. option:: --with-universal-archs=ARCH

Specify the kind of universal binary that should be created. This option is only valid when :option:--enable-universalsdk is set.

Options:

universal2 (x86-64 and arm64);
32-bit (PPC and i386);
64-bit (PPC64 and x86-64);
3-way (i386, PPC and x86-64);
intel (i386 and x86-64);
intel-32 (i386);
intel-64 (x86-64);
all (PPC, i386, PPC64 and x86-64).

Note that values for this configuration item are not the same as the identifiers used for universal binary wheels on macOS. See the Python Packaging User Guide for details on the packaging platform compatibility tags used on macOS <https://packaging.python.org/en/latest/specifications/platform-compatibility-tags/#macos>_

.. option:: --with-framework-name=FRAMEWORK

Specify the name for the python framework on macOS only valid when :option:--enable-framework is set (default: Python).

.. option:: --with-app-store-compliance .. option:: --with-app-store-compliance=PATCH-FILE

The Python standard library contains strings that are known to trigger automated inspection tool errors when submitted for distribution by the macOS and iOS App Stores. If enabled, this option will apply the list of patches that are known to correct app store compliance. A custom patch file can also be specified. This option is disabled by default.

.. versionadded:: 3.13

iOS Options

See :source:iOS/README.rst.

.. option:: --enable-framework=INSTALLDIR

Create a Python.framework. Unlike macOS, the INSTALLDIR argument specifying the installation path is mandatory.

.. option:: --with-framework-name=FRAMEWORK

Specify the name for the framework (default: Python).

Cross Compiling Options

Cross compiling, also known as cross building, can be used to build Python for another CPU architecture or platform. Cross compiling requires a Python interpreter for the build platform. The version of the build Python must match the version of the cross compiled host Python.

.. option:: --build=BUILD

configure for building on BUILD, usually guessed by :program:config.guess.

.. option:: --host=HOST

cross-compile to build programs to run on HOST (target platform)

.. option:: --with-build-python=path/to/python

path to build python binary for cross compiling

.. versionadded:: 3.11

.. option:: CONFIG_SITE=file

An environment variable that points to a file with configure overrides.

Example config.site file:

.. code-block:: ini

  # config.site-aarch64
  ac_cv_buggy_getaddrinfo=no
  ac_cv_file__dev_ptmx=yes
  ac_cv_file__dev_ptc=no

.. option:: HOSTRUNNER

Program to run CPython for the host platform for cross-compilation.

.. versionadded:: 3.11

Cross compiling example::

CONFIG_SITE=config.site-aarch64 ../configure
--build=x86_64-pc-linux-gnu
--host=aarch64-unknown-linux-gnu
--with-build-python=../x86_64/python

Python Build System

Main files of the build system

:file:configure.ac => :file:configure;
:file:Makefile.pre.in => :file:Makefile (created by :file:configure);
:file:pyconfig.h (created by :file:configure);
:file:Modules/Setup: C extensions built by the Makefile using :file:Module/makesetup shell script;

Main build steps

C files (.c) are built as object files (.o).
A static libpython library (.a) is created from objects files.
python.o and the static libpython library are linked into the final python program.
C extensions are built by the Makefile (see :file:Modules/Setup).

Main Makefile targets

make ^^^^

For the most part, when rebuilding after editing some code or refreshing your checkout from upstream, all you need to do is execute make, which (per Make's semantics) builds the default target, the first one defined in the Makefile. By tradition (including in the CPython project) this is usually the all target. The configure script expands an autoconf variable, @DEF_MAKE_ALL_RULE@ to describe precisely which targets make all will build. The three choices are:

profile-opt (configured with --enable-optimizations)
build_wasm (chosen if the host platform matches wasm32-wasi* or wasm32-emscripten)
build_all (configured without explicitly using either of the others)

Depending on the most recent source file changes, Make will rebuild any targets (object files and executables) deemed out-of-date, including running configure again if necessary. Source/target dependencies are many and maintained manually however, so Make sometimes doesn't have all the information necessary to correctly detect all targets which need to be rebuilt. Depending on which targets aren't rebuilt, you might experience a number of problems. If you have build or test problems which you can't otherwise explain, make clean && make should work around most dependency problems, at the expense of longer build times.

make platform ^^^^^^^^^^^^^

Build the python program, but don't build the standard library extension modules. This generates a file named platform which contains a single line describing the details of the build platform, e.g., macosx-14.3-arm64-3.12 or linux-x86_64-3.13.

make profile-opt ^^^^^^^^^^^^^^^^

Build Python using profile-guided optimization (PGO). You can use the configure :option:--enable-optimizations option to make this the default target of the make command (make all or just make).

make clean ^^^^^^^^^^

Remove built files.

make distclean ^^^^^^^^^^^^^^

In addition to the work done by make clean, remove files created by the configure script. configure will have to be run before building again. [#]_

make install ^^^^^^^^^^^^

Build the all target and install Python.

make test ^^^^^^^^^

Build the all target and run the Python test suite with the --fast-ci option without GUI tests. Variables:

TESTOPTS: additional regrtest command-line options.
TESTPYTHONOPTS: additional Python command-line options.
TESTTIMEOUT: timeout in seconds (default: 10 minutes).

make ci ^^^^^^^

This is similar to make test, but uses the -ugui to also run GUI tests.

.. versionadded:: 3.14

make buildbottest ^^^^^^^^^^^^^^^^^

This is similar to make test, but uses the --slow-ci option and default timeout of 20 minutes, instead of --fast-ci option.

make regen-all ^^^^^^^^^^^^^^

Regenerate (almost) all generated files. These include (but are not limited to) bytecode cases, and parser generator file. make regen-stdlib-module-names and autoconf must be run separately for the remaining generated files <#generated-files>_.

C extensions

Some C extensions are built as built-in modules, like the sys module. They are built with the Py_BUILD_CORE_BUILTIN macro defined. Built-in modules have no __file__ attribute:

.. code-block:: pycon

>>> import sys
>>> sys
<module 'sys' (built-in)>
>>> sys.__file__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'sys' has no attribute '__file__'

Other C extensions are built as dynamic libraries, like the _asyncio module. They are built with the Py_BUILD_CORE_MODULE macro defined. Example on Linux x86-64:

.. code-block:: pycon

>>> import _asyncio
>>> _asyncio
<module '_asyncio' from '/usr/lib64/python3.9/lib-dynload/_asyncio.cpython-39-x86_64-linux-gnu.so'>
>>> _asyncio.__file__
'/usr/lib64/python3.9/lib-dynload/_asyncio.cpython-39-x86_64-linux-gnu.so'

:file:Modules/Setup is used to generate Makefile targets to build C extensions. At the beginning of the files, C extensions are built as built-in modules. Extensions defined after the *shared* marker are built as dynamic libraries.

The :c:macro:!PyAPI_FUNC(), :c:macro:!PyAPI_DATA() and :c:macro:PyMODINIT_FUNC macros of :file:Include/exports.h are defined differently depending if the Py_BUILD_CORE_MODULE macro is defined:

Use Py_EXPORTED_SYMBOL if the Py_BUILD_CORE_MODULE is defined
Use Py_IMPORTED_SYMBOL otherwise.

If the Py_BUILD_CORE_BUILTIN macro is used by mistake on a C extension built as a shared library, its :samp:PyInit_{xxx}() function is not exported, causing an :exc:ImportError on import.

Compiler and linker flags

Options set by the ./configure script and environment variables and used by Makefile.

Preprocessor flags

.. envvar:: CONFIGURE_CPPFLAGS

Value of :envvar:CPPFLAGS variable passed to the ./configure script.

.. versionadded:: 3.6

.. envvar:: CPPFLAGS

(Objective) C/C++ preprocessor flags, e.g. :samp:-I{include_dir} if you have headers in a nonstandard directory include_dir.

Both :envvar:CPPFLAGS and :envvar:LDFLAGS need to contain the shell's value to be able to build extension modules using the directories specified in the environment variables.

.. envvar:: BASECPPFLAGS

.. versionadded:: 3.4

.. envvar:: PY_CPPFLAGS

Extra preprocessor flags added for building the interpreter object files.

Default: $(BASECPPFLAGS) -I. -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS).

.. versionadded:: 3.2

Compiler flags

.. envvar:: CC

C compiler command.

Example: gcc -pthread.

.. envvar:: CXX

C++ compiler command.

Example: g++ -pthread.

.. envvar:: CFLAGS

C compiler flags.

.. envvar:: CFLAGS_NODIST

:envvar:CFLAGS_NODIST is used for building the interpreter and stdlib C extensions. Use it when a compiler flag should not be part of :envvar:CFLAGS once Python is installed (:gh:65320).

In particular, :envvar:CFLAGS should not contain:

the compiler flag -I (for setting the search path for include files). The -I flags are processed from left to right, and any flags in :envvar:CFLAGS would take precedence over user- and package-supplied -I flags.
hardening flags such as -Werror because distributions cannot control whether packages installed by users conform to such heightened standards.

.. versionadded:: 3.5

.. envvar:: COMPILEALL_OPTS

Options passed to the :mod:compileall command line when building PYC files in make install. Default: -j0.

.. versionadded:: 3.12

.. envvar:: EXTRA_CFLAGS

Extra C compiler flags.

.. envvar:: CONFIGURE_CFLAGS

Value of :envvar:CFLAGS variable passed to the ./configure script.

.. versionadded:: 3.2

.. envvar:: CONFIGURE_CFLAGS_NODIST

Value of :envvar:CFLAGS_NODIST variable passed to the ./configure script.

.. versionadded:: 3.5

.. envvar:: BASECFLAGS

Base compiler flags.

.. envvar:: OPT

Optimization flags.

.. envvar:: CFLAGS_ALIASING

Strict or non-strict aliasing flags used to compile Python/dtoa.c.

.. versionadded:: 3.7

.. envvar:: CCSHARED

Compiler flags used to build a shared library.

For example, -fPIC is used on Linux and on BSD.

.. envvar:: CFLAGSFORSHARED

Extra C flags added for building the interpreter object files.

Default: $(CCSHARED) when :option:--enable-shared is used, or an empty string otherwise.

.. envvar:: PY_CFLAGS

Default: $(BASECFLAGS) $(OPT) $(CONFIGURE_CFLAGS) $(CFLAGS) $(EXTRA_CFLAGS).

.. envvar:: PY_CFLAGS_NODIST

Default: $(CONFIGURE_CFLAGS_NODIST) $(CFLAGS_NODIST) -I$(srcdir)/Include/internal.

.. versionadded:: 3.5

.. envvar:: PY_STDMODULE_CFLAGS

C flags used for building the interpreter object files.

Default: $(PY_CFLAGS) $(PY_CFLAGS_NODIST) $(PY_CPPFLAGS) $(CFLAGSFORSHARED).

.. versionadded:: 3.7

.. envvar:: PY_CORE_CFLAGS

Default: $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE.

.. versionadded:: 3.2

.. envvar:: PY_BUILTIN_MODULE_CFLAGS

Compiler flags to build a standard library extension module as a built-in module, like the :mod:posix module.

Default: $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN.

.. versionadded:: 3.8

.. envvar:: PURIFY

Purify command. Purify is a memory debugger program.

Default: empty string (not used).

Linker flags

.. envvar:: LINKCC

Linker command used to build programs like python and _testembed.

Default: $(PURIFY) $(CC).

.. envvar:: CONFIGURE_LDFLAGS

Value of :envvar:LDFLAGS variable passed to the ./configure script.

Avoid assigning :envvar:CFLAGS, :envvar:LDFLAGS, etc. so users can use them on the command line to append to these values without stomping the pre-set values.

.. versionadded:: 3.2

.. envvar:: LDFLAGS_NODIST

:envvar:LDFLAGS_NODIST is used in the same manner as :envvar:CFLAGS_NODIST. Use it when a linker flag should not be part of :envvar:LDFLAGS once Python is installed (:gh:65320).

In particular, :envvar:LDFLAGS should not contain:

the compiler flag -L (for setting the search path for libraries). The -L flags are processed from left to right, and any flags in :envvar:LDFLAGS would take precedence over user- and package-supplied -L flags.

.. envvar:: CONFIGURE_LDFLAGS_NODIST

Value of :envvar:LDFLAGS_NODIST variable passed to the ./configure script.

.. versionadded:: 3.8

.. envvar:: LDFLAGS

Linker flags, e.g. :samp:-L{lib_dir} if you have libraries in a nonstandard directory lib_dir.

Both :envvar:CPPFLAGS and :envvar:LDFLAGS need to contain the shell's value to be able to build extension modules using the directories specified in the environment variables.

Please consider using EXE_LDFLAGS if the supplied linker flags are executable specific, e.g. GCC's -pie flag.

.. envvar:: LIBS

Linker flags to pass libraries to the linker when linking the Python executable.

Example: -lrt.

.. envvar:: LDSHARED

Command to build a shared library.

Default: @LDSHARED@ $(PY_LDFLAGS).

.. envvar:: BLDSHARED

Command to build libpython shared library.

Default: @BLDSHARED@ $(PY_CORE_LDFLAGS).

.. envvar:: PY_LDFLAGS

Default: $(CONFIGURE_LDFLAGS) $(LDFLAGS).

.. envvar:: PY_LDFLAGS_NODIST

Default: $(CONFIGURE_LDFLAGS_NODIST) $(LDFLAGS_NODIST).

.. versionadded:: 3.8

.. envvar:: PY_CORE_LDFLAGS

Linker flags used for building the interpreter object files.

.. versionadded:: 3.8

.. envvar:: EXE_LDFLAGS

Linker flags used for building executable targets such as the interpreter. If supplied, :envvar:PY_CORE_EXE_LDFLAGS will be used in replacement of :envvar:PY_CORE_LDFLAGS.

.. versionadded:: 3.15

.. envvar:: CONFIGURE_EXE_LDFLAGS

Value of :envvar:EXE_LDFLAGS variable passed to the ./configure script.

.. versionadded:: 3.15

.. envvar:: PY_CORE_EXE_LDFLAGS

Linker flags used for building the interpreter and executable targets.

Default: $(PY_CORE_LDFLAGS)

.. versionadded:: 3.15

.. rubric:: Footnotes

.. [#] git clean -fdx is an even more extreme way to "clean" your checkout. It removes all files not known to Git. When bug hunting using git bisect, this is recommended between probes <https://github.com/python/cpython/issues/114505#issuecomment-1907021718>_ to guarantee a completely clean build. Use with care, as it will delete all files not checked into Git, including your new, uncommitted work.