3. Configure Python

3.1. Configure Options

List all ./configure script options using:

./configure --help

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

3.1.1. General Options


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

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

New 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 number of bits is selected depending on sizeof(void*): 30 bits if void* size is 64-bit or larger, 15 bits otherwise.

Define the PYLONG_BITS_IN_DIGIT to 15 or 30.

See sys.int_info.bits_per_digit.


Compile the Python main() function and link Python executable with C++ compiler: $CXX, or COMPILER if specified.


Set the Python executable suffix to SUFFIX.

The default suffix is .exe on Windows and macOS (python.exe executable), and an empty string on other platforms (python executable).

--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.

New 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.

New in version 3.9.


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.



Python library directory name (default is lib).

Fedora and SuSE use lib64 on 64-bit platforms.

See sys.platlibdir.

New 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.

New in version 3.10.

3.1.2. Install Options


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

New 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;

New in version 3.6.

3.1.3. Performance options

Configuring Python using --enable-optimizations --with-lto (PGO + LTO) is recommended for best 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.

New in version 3.6.

Changed in version 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).

New 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).

New in version 3.6.


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).

3.1.4. 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 PYTHONTHREADDEBUG environment variable.

  • Add support for the __ltrace__ 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 surroundeded 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.

    • 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.

Changed in version 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.

3.1.5. 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).

New 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.

New in version 3.6.


Enable Valgrind support (default is no).


Enable DTrace support (default is no).

See Instrumenting CPython with DTrace and SystemTap.

New in version 3.6.


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

New in version 3.6.


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

New in version 3.6.


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

New in version 3.6.

3.1.6. 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).

New in version 3.10.

3.1.7. 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 _ctypes extension module using an installed ffi library, see the ctypes module (default is system-dependent).


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

New in version 3.3.


Use editline library for backend of the readline module.

Define the WITH_EDITLINE macro.

New in version 3.10.


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

Don’t define the HAVE_LIBREADLINE macro.

New in version 3.10.


Override search for Tcl and Tk include files.


Override search for Tcl and Tk libraries.


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.

New 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.

New in version 3.10.

3.1.8. Security Options


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

  • siphash24 (default).

  • fnv;

New in version 3.4.


Built-in hash modules:

  • md5;

  • sha1;

  • sha256;

  • sha512;

  • sha3 (with shake);

  • blake2.

New 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.

New in version 3.7.

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

3.1.9. 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).

3.2. Python Build System

3.2.1. 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;

  • setup.py: C extensions built using the distutils module.

3.2.2. 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) and python setup.py build.

3.2.3. 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.

3.2.4. 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 extensins 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 setup.py script only builds C extensions as shared libraries using the distutils module.

The PyAPI_FUNC(), PyAPI_API() and PyMODINIT_FUNC() macros of Include/pyport.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.

3.3. Compiler and linker flags

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

3.3.1. Preprocessor flags


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

New in version 3.6.


(Objective) C/C++ preprocessor flags, e.g. -I<include dir> if you have headers in a nonstandard directory <include dir>.

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


New in version 3.4.


Extra preprocessor flags added for building the interpreter object files.

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

New in version 3.2.

3.3.2. Compiler flags


C compiler command.

Example: gcc -pthread.


C compiler command used to build the main() function of programs like python.

Variable set by the --with-cxx-main option of the configure script.

Default: $(CC).


C++ compiler command.

Used if the --with-cxx-main option is used.

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 the distutils CFLAGS once Python is installed (bpo-21121).

New in version 3.5.


Extra C compiler flags.


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

New in version 3.2.


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

New in version 3.5.


Base compiler flags.


Optimization flags.


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

New 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.

New in version 3.5.


C flags used for building the interpreter object files.


New in version 3.7.



New in version 3.2.


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


New in version 3.8.


Purify command. Purify is a memory debugger program.

Default: empty string (not used).

3.3.3. Linker flags


Linker command used to build programs like python and _testembed.

Default: $(PURIFY) $(MAINCC).


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.

New 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 the distutils LDFLAGS once Python is installed (bpo-35257).


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

New in version 3.8.


Linker flags, e.g. -L<lib dir> if you have libraries in a nonstandard directory <lib dir>.

Both CPPFLAGS and LDFLAGS need to contain the shell’s value for setup.py 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.






New in version 3.8.


Linker flags used for building the interpreter object files.

New in version 3.8.