3. Configure Python¶

3.1.1. Requirements for optional modules¶

Some optional modules 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 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:

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

3.2.1. 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 2.72, aclocal from Automake 1.16.5, and pkg-config 1.8.1.

3.3.1. General Options¶

--enable-loadable-sqlite-extensions¶

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

See the sqlite3.Connection.enable_load_extension() method of the sqlite3 module.

Added in version 3.6.

--disable-ipv6¶

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

--enable-big-digits=[15|30]¶

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

By default, the digit size is 30.

Define the PYLONG_BITS_IN_DIGIT to 15 or 30.

See sys.int_info.bits_per_digit.

--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).

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

--with-tzpath=<list of absolute paths separated by pathsep>¶

Select the default time zone search path for zoneinfo.TZPATH. See the Compile-time configuration of the zoneinfo module.

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

See os.pathsep path separator.

Added in version 3.9.

--without-decimal-contextvar¶

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

See decimal.HAVE_CONTEXTVAR and the contextvars module.

Added in version 3.9.

--with-dbmliborder=<list of backend names>¶

Override order to check db backends for the dbm module

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

• ndbm;

• gdbm;

• bdb.

--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 PYTHONCOERCECLOCALE and the PEP 538.

--with-platlibdir=DIRNAME¶

Python library directory name (default is lib).

Fedora and SuSE use lib64 on 64-bit platforms.

See sys.platlibdir.

Added in version 3.9.

--with-wheel-pkg-dir=PATH¶

Directory of wheel packages used by the 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 ensurepip._bundled package.

Added in version 3.10.

--with-pkg-config=[check|yes|no]¶

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

• check (default): pkg-config is optional

• yes: pkg-config is mandatory

• no: configure does not use pkg-config even when present

Added in version 3.11.

--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 -X pystats command line option.

• Add PYTHONSTATS environment variable.

• Define the Py_STATS macro.

• Add functions to the sys module:

  • sys._stats_on(): Turns on statistics gathering.

  • sys._stats_off(): Turns off statistics gathering.

  • sys._stats_clear(): Clears the statistics.

  • 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.

Added in version 3.11.

--disable-gil¶

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

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

See Free-threaded CPython for more detail.

Added in version 3.13.

--enable-experimental-jit=[no|yes|yes-off|interpreter]¶

Indicate how to integrate the experimental just-in-time compiler.

• no: Don’t build the JIT.

• yes: Enable the JIT. To disable it at runtime, set the environment variable PYTHON_JIT=0.

• yes-off: Build the JIT, but disable it by default. To enable it at runtime, set the environment variable PYTHON_JIT=1.

• interpreter: Enable the “JIT interpreter” (only useful for those debugging the JIT itself). To disable it at runtime, set the environment variable PYTHON_JIT=0.

--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 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.

Added in version 3.13.

PKG_CONFIG¶

Path to pkg-config utility.

PKG_CONFIG_LIBDIR¶

PKG_CONFIG_PATH¶

pkg-config options.

3.3.2. C compiler options¶

CC¶

C compiler command.

CFLAGS¶

C compiler flags.

CPP¶

C preprocessor command.

CPPFLAGS¶

C preprocessor flags, e.g. -Iinclude_dir.

3.3.3. Linker options¶

LDFLAGS¶

Linker flags, e.g. -Llibrary_directory.

LIBS¶

Libraries to pass to the linker, e.g. -llibrary.

MACHDEP¶

Name for machine-dependent library files.

3.3.4. Options for third-party dependencies¶

BZIP2_CFLAGS¶

BZIP2_LIBS¶

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

CURSES_CFLAGS¶

CURSES_LIBS¶

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

GDBM_CFLAGS¶

GDBM_LIBS¶

C compiler and linker flags for gdbm.

LIBEDIT_CFLAGS¶

LIBEDIT_LIBS¶

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

LIBFFI_CFLAGS¶

LIBFFI_LIBS¶

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

LIBMPDEC_CFLAGS¶

LIBMPDEC_LIBS¶

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

Note

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

LIBLZMA_CFLAGS¶

LIBLZMA_LIBS¶

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

LIBREADLINE_CFLAGS¶

LIBREADLINE_LIBS¶

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

LIBSQLITE3_CFLAGS¶

LIBSQLITE3_LIBS¶

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

LIBUUID_CFLAGS¶

LIBUUID_LIBS¶

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

LIBZSTD_CFLAGS¶

LIBZSTD_LIBS¶

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

Added in version 3.14.

PANEL_CFLAGS¶

PANEL_LIBS¶

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

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

TCLTK_CFLAGS¶

TCLTK_LIBS¶

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

ZLIB_CFLAGS¶

ZLIB_LIBS¶

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

3.3.5. WebAssembly Options¶

--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.

Added in version 3.11.

--enable-wasm-pthreads¶

Turn on pthreads support for WASM.

Added in version 3.11.

3.3.6. Install Options¶

--prefix=PREFIX¶

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

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

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

--exec-prefix=EPREFIX¶

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

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

--disable-test-modules¶

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

Added in version 3.10.

--with-ensurepip=[upgrade|install|no]¶

Select the 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;

Added in version 3.6.

3.3.7. 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.

--enable-optimizations¶

Enable Profile Guided Optimization (PGO) using 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 CFLAGS.

Added in version 3.6.

Changed in version 3.10: Use -fno-semantic-interposition on GCC.

PROFILE_TASK¶

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

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

Added in version 3.8.

Changed in version 3.13: Task failure is no longer ignored silently.

--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).

Added in version 3.6.

Added in version 3.11: To use ThinLTO feature, use --with-lto=thin on Clang.

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

--enable-bolt¶

Enable usage of the BOLT post-link binary optimizer (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 BOLT_INSTRUMENT_FLAGS and BOLT_APPLY_FLAGS configure variables can be defined to override the default set of arguments for llvm-bolt to instrument and apply BOLT data to binaries, respectively.

Added in version 3.12.

BOLT_APPLY_FLAGS¶

Arguments to llvm-bolt when creating a BOLT optimized binary.

Added in version 3.12.

BOLT_INSTRUMENT_FLAGS¶

Arguments to llvm-bolt when instrumenting binaries.

Added in version 3.12.

--with-computed-gotos¶

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

--with-tail-call-interp¶

Enable interpreters using tail calls in CPython. If enabled, enabling PGO (--enable-optimizations) is highly recommended. This option specifically requires a C compiler with proper tail call support, and the preserve_none calling convention. For example, Clang 19 and newer supports this feature.

Added in version 3.14.

--without-mimalloc¶

Disable the fast mimalloc allocator (enabled by default).

See also PYTHONMALLOC environment variable.

--without-pymalloc¶

Disable the specialized Python memory allocator pymalloc (enabled by default).

See also PYTHONMALLOC environment variable.

--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.

--enable-profiling¶

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

--with-strict-overflow¶

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

--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.

Py_REMOTE_DEBUG¶

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

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

Added in version 3.14.

3.3.8. Python Debug Build¶

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

Effects of a debug build:

• Display all warnings by default: the list of default warning filters is empty in the warnings module.

• Add d to sys.abiflags.

• Add sys.gettotalrefcount() function.

• Add -X showrefcount command line option.

• Add -d command line option and 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 debug hooks on 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 --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 (gc.collect() function) runs some basic checks on objects consistency.

  • The Py_SAFE_DOWNCAST() macro checks for integer underflow and overflow when downcasting from wide types to narrow types.

See also the Python Development Mode and the --with-trace-refs configure option.

3.3.9. Debug options¶

--with-pydebug¶

Build Python in debug mode: define the Py_DEBUG macro (disabled by default).

--with-trace-refs¶

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

Effects:

• Define the Py_TRACE_REFS macro.

• Add sys.getobjects() function.

• Add PYTHONDUMPREFS environment variable.

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

Statically allocated objects are not traced.

Added in version 3.8.

Changed in version 3.13: This build is now ABI compatible with release build and debug build.

--with-assertions¶

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

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

See also the --with-pydebug option (debug build) which also enables assertions.

Added in version 3.6.

--with-valgrind¶

Enable Valgrind support (default is no).

--with-dtrace¶

Enable DTrace support (default is no).

See Instrumenting CPython with DTrace and SystemTap.

Added in version 3.6.

--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 --without-pymalloc to disable the specialized small-object allocator whose allocations are not tracked by ASan.

Added in version 3.6.

--with-memory-sanitizer¶

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

Added in version 3.6.

--with-undefined-behavior-sanitizer¶

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

Added in version 3.6.

--with-thread-sanitizer¶

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

Added in version 3.13.

3.3.10. Linker options¶

--enable-shared¶

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

--without-static-libpython¶

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

Added in version 3.10.

3.3.11. Libraries options¶

--with-libs='lib1 ...'¶

Link against additional libraries (default is no).

--with-system-expat¶

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

--with-system-libmpdec¶

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

Added in version 3.3.

Changed in version 3.13: Default to using the installed mpdecimal library.

Changed in version 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 since version 3.13, will be removed in version 3.16: A copy of the mpdecimal library sources will no longer be distributed with Python 3.16.

See also

LIBMPDEC_CFLAGS and LIBMPDEC_LIBS.

--with-readline=readline|editline¶

Designate a backend library for the readline module.

• readline: Use readline as the backend.

• editline: Use editline as the backend.

Added in version 3.10.

--without-readline¶

Don’t build the readline module (built by default).

Don’t define the HAVE_LIBREADLINE macro.

Added in version 3.10.

--with-libm=STRING¶

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

--with-libc=STRING¶

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

--with-openssl=DIR¶

Root of the OpenSSL directory.

Added in version 3.7.

--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 --with-openssl and pkg-config;

• DIR: set an explicit rpath.

Added in version 3.10.

3.3.12. Security Options¶

--with-hash-algorithm=[fnv|siphash13|siphash24]¶

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

• siphash13 (default);

• siphash24;

• fnv.

Added in version 3.4.

Added in version 3.11: siphash13 is added and it is the new default.

--with-builtin-hashlib-hashes=md5,sha1,sha256,sha512,sha3,blake2¶

Built-in hash modules:

• md5;

• sha1;

• sha256;

• sha512;

• sha3 (with shake);

• blake2.

Added in version 3.9.

--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 ssl module.

Added in version 3.7.

Changed in version 3.10: The settings python and STRING also set TLS 1.2 as minimum protocol version.

--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 --disable-safety:

• -fstack-protector-strong: Enable run-time checks for stack-based buffer overflows.

• -Wtrampolines: Enable warnings about trampolines that require executable stacks.

Added in version 3.14.

--enable-slower-safety¶

Enable compiler options that are