3. Configure Python

3.1. Build Requirements

Features required to build CPython:

Zmienione w wersji 3.5: On Windows, Visual Studio 2015 or later is required.

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

Zmienione w wersji 3.7: Thread support and OpenSSL 1.0.2 are now required.

Zmienione w wersji 3.10: OpenSSL 1.1.1 is now required.

Zmienione w wersji 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”.

3.2. 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.

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 autoconf-archive, aclocal and pkg-config versions.

3.3. Configure Options

List all ./configure script options using:

./configure --help

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

3.3.1. General Options


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


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.


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).

Zmienione w wersji 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.


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.


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

Don’t define the PY_COERCE_C_LOCALE macro.



Disable all freelists except the empty tuple singleton.

Added in version 3.11.


Python library directory name (default is lib).

Fedora and SuSE use lib64 on 64-bit platforms.

See sys.platlibdir.

Added in version 3.9.


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.


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.


Turn on internal statistics gathering.

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

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

Added in version 3.11.

3.3.2. WebAssembly Options


Set build flavor for wasm32-emscripten.

  • browser (default): preload minimal stdlib, default MEMFS.

  • node: NODERAWFS and pthread support.

Added in version 3.11.


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.


Turn on pthreads support for WASM.

Added in version 3.11.

3.3.3. Install Options


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.


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

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


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.


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.

3.3.4. 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 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.


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.

Zmienione w wersji 3.10: Use -fno-semantic-interposition on GCC.


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.


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.

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


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.


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


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

See also PYTHONMALLOC environment variable.


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


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

3.3.5. 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.

Zmienione w wersji 3.8: Release builds and debug builds are now ABI compatible: defining the Py_DEBUG macro no longer implies the Py_TRACE_REFS macro (see the --with-trace-refs option), which introduces the only ABI incompatibility.

3.3.6. Debug options


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


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


  • Define the Py_TRACE_REFS macro.

  • Add sys.getobjects() function.

  • Add PYTHONDUMPREFS environment variable.

This build is not ABI compatible with release build (default build) or debug build (Py_DEBUG and Py_REF_DEBUG macros).

Added in version 3.8.


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.


Enable Valgrind support (default is no).


Enable DTrace support (default is no).

See Instrumenting CPython with DTrace and SystemTap.

Added in version 3.6.


Enable AddressSanitizer memory error detector, asan (default is no).

Added in version 3.6.


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

Added in version 3.6.


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

Added in version 3.6.

3.3.7. Linker options


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


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

Added in version 3.10.

3.3.8. Libraries options

--with-libs='lib1 ...'

Link against additional libraries (default is no).


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


Build the _decimal extension module using an installed mpdec library, see the decimal module (default is no).

Added in version 3.3.


Use editline library for backend of the readline module.

Define the WITH_EDITLINE macro.

Added in version 3.10.


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

Don’t define the HAVE_LIBREADLINE macro.

Added in version 3.10.


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


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


Root of the OpenSSL directory.

Added in version 3.7.


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.

3.3.9. Security Options


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.


Built-in hash modules:

  • md5;

  • sha1;

  • sha256;

  • sha512;

  • sha3 (with shake);

  • blake2.

Added in version 3.9.


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.

Zmienione w wersji 3.10: The settings python and STRING also set TLS 1.2 as minimum protocol version.

3.3.10. macOS Options

See Mac/README.rst.


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


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


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


  • universal2;

  • 32-bit;

  • 64-bit;

  • 3-way;

  • intel;

  • intel-32;

  • intel-64;

  • all.


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

3.3.11. 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.


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


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


path to build python binary for cross compiling

Added in version 3.11.


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

Example config.site file:

# config.site-aarch64

Cross compiling example:

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

3.4. Python Build System

3.4.1. Main files of the build system

  • configure.ac => configure;

  • Makefile.pre.in => Makefile (created by configure);

  • pyconfig.h (created by configure);

  • Modules/Setup: C extensions built by the Makefile using Module/makesetup shell script;

3.4.2. 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 Modules/Setup).

3.4.3. Main Makefile targets

  • make: Build Python with the standard library.

  • make platform:: build the python program, but don’t build the standard library extension modules.

  • make profile-opt: build Python using Profile Guided Optimization (PGO). You can use the configure --enable-optimizations option to make this the default target of the make command (make all or just make).

  • make buildbottest: Build Python and run the Python test suite, the same way than buildbots test Python. Set TESTTIMEOUT variable (in seconds) to change the test timeout (1200 by default: 20 minutes).

  • make install: Build and install Python.

  • make regen-all: Regenerate (almost) all generated files; make regen-stdlib-module-names and autoconf must be run separately for the remaining generated files.

  • make clean: Remove built files.

  • make distclean: Same than make clean, but remove also files created by the configure script.

3.4.4. 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:

>>> 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:

>>> import _asyncio
>>> _asyncio
<module '_asyncio' from '/usr/lib64/python3.9/lib-dynload/_asyncio.cpython-39-x86_64-linux-gnu.so'>
>>> _asyncio.__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 PyAPI_FUNC(), PyAPI_DATA() and PyMODINIT_FUNC macros of 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 PyInit_xxx() function is not exported, causing an ImportError on import.

3.5. Compiler and linker flags

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

3.5.1. Preprocessor flags


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

Added in version 3.6.


(Objective) C/C++ preprocessor flags, e.g. -Iinclude_dir if you have headers in a nonstandard directory include_dir.

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


Added in version 3.4.


Extra preprocessor flags added for building the interpreter object files.

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

Added in version 3.2.

3.5.2. Compiler flags


C compiler command.

Example: gcc -pthread.


C++ compiler command.

Example: g++ -pthread.


C compiler flags.


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

In particular, 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 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.

Added in version 3.5.


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

Added in version 3.12.


Extra C compiler flags.


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

Added in version 3.2.


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

Added in version 3.5.


Base compiler flags.


Optimization flags.


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

Added in version 3.7.


Compiler flags used to build a shared library.

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


Extra C flags added for building the interpreter object files.

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




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

Added in version 3.5.


C flags used for building the interpreter object files.


Added in version 3.7.



Added in version 3.2.


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


Added in version 3.8.


Purify command. Purify is a memory debugger program.

Default: empty string (not used).

3.5.3. Linker flags


Linker command used to build programs like python and _testembed.

Default: $(PURIFY) $(CC).


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

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

Added in version 3.2.


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

In particular, 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 LDFLAGS would take precedence over user- and package-supplied -L flags.


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

Added in version 3.8.


Linker flags, e.g. -Llib_dir if you have libraries in a nonstandard directory lib_dir.

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


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

Example: -lrt.


Command to build a shared library.



Command to build libpython shared library.






Added in version 3.8.


Linker flags used for building the interpreter object files.

Added in version 3.8.