# 3. Configure Python

## 3.1. Build Requirements

Features and minimum versions required to build CPython:

- A C11 compiler. Optional C11 features are not required.

- On Windows, Microsoft Visual Studio 2017 or later is required.

- Support for IEEE 754 floating-point numbers and floating-point Not-a-Number (NaN).

- Support for threads.

- OpenSSL 1.1.1 is the minimum version and OpenSSL 3.0.18 is the recommended minimum version for the `ssl` and `hashlib` extension modules.

- SQLite 3.15.2 for the `sqlite3` extension module.

- Tcl/Tk 8.5.12 for the `tkinter` module.

- libmpdec 2.5.0 for the `decimal` module.

- Autoconf 2.71 and aclocal 1.16.5 are required to regenerate the `configure` script.

Ändrad i version 3.1: Tcl/Tk version 8.3.1 is now required.

Ändrad i version 3.5: On Windows, Visual Studio 2015 or later is now required. Tcl/Tk version 8.4 is now required.

Ändrad i version 3.6: Selected C99 features are now required, like `<stdint.h>` and `static inline` functions.

Ändrad i version 3.7: Thread support and OpenSSL 1.0.2 are now required.

Ändrad i version 3.10: OpenSSL 1.1.1 is now required. Require SQLite 3.7.15.

Ändrad i version 3.11: C11 compiler, IEEE 754 and NaN support are now required. On Windows, Visual Studio 2017 or later is required. Tcl/Tk version 8.5.12 is now required for the `tkinter` module.

Ändrad i version 3.13: Autoconf 2.71, aclocal 1.16.5 and SQLite 3.15.2 are now 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

--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.

  Tillagd i 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).

  Ändrad i 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.

  Tillagd i 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.

  Tillagd i 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.

--without-freelists

  Disable all freelists except the empty tuple singleton.

  Tillagd i version 3.11.

--with-platlibdir=DIRNAME

  Python library directory name (default is `lib`).

  Fedora and SuSE use `lib64` on 64-bit platforms.

  See `sys.platlibdir`.

  Tillagd i 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.

  Tillagd i 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

  Tillagd i 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.

  Tillagd i version 3.11.

--disable-gil

  Enables experimental 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.

  Tillagd i version 3.13.

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

  Indicate how to integrate the JIT compiler.

  - `no` - build the interpreter without the JIT.

  - `yes` - build the interpreter with the JIT.

  - `yes-off` - build the interpreter with the JIT but disable it by default.

  - `interpreter` - build the interpreter without the JIT, but with the tier 2 enabled interpreter.

  By convention, `--enable-experimental-jit` is a shorthand for `--enable-experimental-jit=yes`.

  Anteckning

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

  Tillagd i 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

Tillagd i version 3.11.

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`.

LIBB2_CFLAGS

LIBB2_LIBS

  C compiler and linker flags for `libb2` (BLAKE2), used by `hashlib` module, overriding `pkg-config`.

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`.

  Anteckning

  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`.

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

--with-emscripten-target=[browser|node]

  Set build flavor for `wasm32-emscripten`.

  - `browser` (default): preload minimal stdlib, default MEMFS.

  - `node`: NODERAWFS and pthread support.

  Tillagd i version 3.11.

--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.

  Tillagd i version 3.11.

--enable-wasm-pthreads

  Turn on pthreads support for WASM.

  Tillagd i 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).

  Tillagd i 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;

  Tillagd i 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.

  Anteckning

  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`.

  Tillagd i version 3.6.

  Ändrad i 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)`.

  Tillagd i version 3.8.

  Ändrad i 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`).

  Tillagd i version 3.6.

  Tillagd i version 3.11: To use ThinLTO feature, use `--with-lto=thin` on Clang.

  Ändrad i 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.

  Tillagd i version 3.12.

BOLT_APPLY_FLAGS

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

  Tillagd i version 3.12.

BOLT_INSTRUMENT_FLAGS

  Arguments to `llvm-bolt` when instrumenting binaries.

  Tillagd i version 3.12.

--with-computed-gotos

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

--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).

### 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.

Ändrad i 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).

### 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.

  Tillagd i version 3.8.

  Ändrad i 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.

  Tillagd i 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.

  Tillagd i 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.

  Tillagd i version 3.6.

--with-memory-sanitizer

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

  Tillagd i version 3.6.

--with-undefined-behavior-sanitizer

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

  Tillagd i version 3.6.

--with-thread-sanitizer

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

  Tillagd i 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).

  Tillagd i 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).

  Tillagd i version 3.3.

  Ändrad i version 3.13: Default to using the installed `mpdecimal` library.

  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.

  Se även

  `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.

  Tillagd i version 3.10.

--without-readline

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

  Don’t define the `HAVE_LIBREADLINE` macro.

  Tillagd i 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.

  Tillagd i 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.

  Tillagd i 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`.

  Tillagd i version 3.4.

  Tillagd i 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`.

  Tillagd i 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.

  Tillagd i version 3.7.

  Ändrad i version 3.10: The settings `python` and STRING also set TLS 1.2 as minimum protocol version.

### 3.3.13. macOS Options

See Mac/README.rst.

--enable-universalsdk

--enable-universalsdk=SDKDIR

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

--enable-framework

--enable-framework=INSTALLDIR

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

--with-universal-archs=ARCH

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

--with-framework-name=FRAMEWORK

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

--with-app-store-compliance

--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.

  Tillagd i version 3.13.

### 3.3.14. iOS Options

See iOS/README.rst.

--enable-framework=INSTALLDIR

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

--with-framework-name=FRAMEWORK

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

### 3.3.15. 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.

--build=BUILD

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

--host=HOST

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

--with-build-python=path/to/python

  path to build `python` binary for cross compiling

  Tillagd i version 3.11.

CONFIG_SITE=file

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

  Example config.site file:

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

HOSTRUNNER

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

  Tillagd i version 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

## 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

#### 3.4.3.1. 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` (configured with `--with-emscripten-target`)

- `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.

#### 3.4.3.2. 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`.

#### 3.4.3.3. 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`).

#### 3.4.3.4. make clean

Remove built files.

#### 3.4.3.5. 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. [1]

#### 3.4.3.6. make install

Build the `all` target and install Python.

#### 3.4.3.7. make test

Build the `all` target and run the Python test suite with the `--fast-ci` option. Variables:

- `TESTOPTS`: additional regrtest command-line options.

- `TESTPYTHONOPTS`: additional Python command-line options.

- `TESTTIMEOUT`: timeout in seconds (default: 10 minutes).

#### 3.4.3.8. 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.

#### 3.4.3.9. 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.

### 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__
    '/usr/lib64/python3.9/lib-dynload/_asyncio.cpython-39-x86_64-linux-gnu.so'

`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

CONFIGURE_CPPFLAGS

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

  Tillagd i version 3.6.

CPPFLAGS

  (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.

BASECPPFLAGS

  Tillagd i version 3.4.

PY_CPPFLAGS

  Extra preprocessor flags added for building the interpreter object files.

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

  Tillagd i version 3.2.

### 3.5.2. Compiler flags

CC

  C compiler command.

  Example: `gcc -pthread`.

CXX

  C++ compiler command.

  Example: `g++ -pthread`.

CFLAGS

  C compiler flags.

CFLAGS_NODIST

  `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.

  Tillagd i version 3.5.

COMPILEALL_OPTS

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

  Tillagd i version 3.12.

EXTRA_CFLAGS

  Extra C compiler flags.

CONFIGURE_CFLAGS

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

  Tillagd i version 3.2.

CONFIGURE_CFLAGS_NODIST

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

  Tillagd i version 3.5.

BASECFLAGS

  Base compiler flags.

OPT

  Optimization flags.

CFLAGS_ALIASING

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

  Tillagd i version 3.7.

CCSHARED

  Compiler flags used to build a shared library.

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

CFLAGSFORSHARED

  Extra C flags added for building the interpreter object files.

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

PY_CFLAGS

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

PY_CFLAGS_NODIST

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

  Tillagd i version 3.5.

PY_STDMODULE_CFLAGS

  C flags used for building the interpreter object files.

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

  Tillagd i version 3.7.

PY_CORE_CFLAGS

  Default: `$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE`.

  Tillagd i version 3.2.

PY_BUILTIN_MODULE_CFLAGS

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

  Default: `$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN`.

  Tillagd i version 3.8.

PURIFY

  Purify command. Purify is a memory debugger program.

  Default: empty string (not used).

### 3.5.3. Linker flags

LINKCC

  Linker command used to build programs like `python` and `_testembed`.

  Default: `$(PURIFY) $(CC)`.

CONFIGURE_LDFLAGS

  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.

  Tillagd i version 3.2.

LDFLAGS_NODIST

  `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.

CONFIGURE_LDFLAGS_NODIST

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

  Tillagd i version 3.8.

LDFLAGS

  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.

LIBS

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

  Example: `-lrt`.

LDSHARED

  Command to build a shared library.

  Default: `@LDSHARED@ $(PY_LDFLAGS)`.

BLDSHARED

  Command to build `libpython` shared library.

  Default: `@BLDSHARED@ $(PY_CORE_LDFLAGS)`.

PY_LDFLAGS

  Default: `$(CONFIGURE_LDFLAGS) $(LDFLAGS)`.

PY_LDFLAGS_NODIST

  Default: `$(CONFIGURE_LDFLAGS_NODIST) $(LDFLAGS_NODIST)`.

  Tillagd i version 3.8.

PY_CORE_LDFLAGS

  Linker flags used for building the interpreter object files.

  Tillagd i version 3.8.

Footnotes

[1]

`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 to guarantee a completely clean build. Use with care, as it will delete all files not checked into Git, including your new, uncommitted work.