3. Configure Python¶
3.1. Build Requirements¶
Features required to build CPython:
A C11 compiler. Optional C11 features are not required.
Support for IEEE 754 floating point numbers and floating point Not-a-Number (NaN).
Support for threads.
On Windows, Microsoft Visual Studio 2017 or later is required.
Changed in version 3.11: C11 compiler, IEEE 754 and NaN support are now required. On Windows, Visual Studio 2017 or later is required.
Changed in version 3.10: OpenSSL 1.1.1 is now required.
Changed in version 3.7: Thread support and OpenSSL 1.0.2 are now required.
Changed in version 3.6: Selected C99 features are now required, like <stdint.h>
and static
inline
functions.
Changed in version 3.5: On Windows, Visual Studio 2015 or later is required.
See also PEP 7 “Style Guide for C Code” and PEP 11 “CPython platform support”.
3.2. Configure Options¶
List all ./configure
script options using:
./configure --help
See also the Misc/SpecialBuilds.txt
in the Python source distribution.
3.2.1. General Options¶
- --enable-loadable-sqlite-extensions¶
Support loadable extensions in the
_sqlite
extension module (default is no).See the
sqlite3.Connection.enable_load_extension()
method of thesqlite3
module.New in version 3.6.
- --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
to15
or30
.
- --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 thezoneinfo
module.Default:
/usr/share/zoneinfo:/usr/lib/zoneinfo:/usr/share/lib/zoneinfo:/etc/zoneinfo
.See
os.pathsep
path separator.New 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 thedecimal
module.See
decimal.HAVE_CONTEXTVAR
and thecontextvars
module.New in version 3.9.
- --with-dbmliborder=<list of backend names>¶
Override order to check db backends for the
dbm
moduleA 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.
New in 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
.New 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 theensurepip._bundled
package.New 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 optionalyes
: pkg-config is mandatoryno
: configure does not use pkg-config even when present
New in version 3.11.
- --enable-pystats¶
Turn on internal statistics gathering.
The statistics will be dumped to a arbitrary (probably unique) file in
/tmp/py_stats/
, orC:\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.New in version 3.11.
3.2.2. 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.
New in 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.New in version 3.11.
- --enable-wasm-pthreads¶
Turn on pthreads support for WASM.
New in version 3.11.
3.2.3. Install Options¶
3.2.4. 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-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.New 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)
.New in version 3.8.
- --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
orlld
).New in version 3.6.
New 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
andmerge-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.
New in version 3.12.
- --with-computed-gotos¶
Enable computed gotos in evaluation loop (enabled by default on supported compilers).
- --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).
3.2.5. 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
tosys.abiflags
.Add
sys.gettotalrefcount()
function.Add
-X showrefcount
command line option.Add
-d
command line option andPYTHONDEBUG
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
andPy_REF_DEBUG
macros.Add runtime checks: code surrounded by
#ifdef Py_DEBUG
and#endif
. Enableassert(...)
and_PyObject_ASSERT(...)
assertions: don’t set theNDEBUG
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.
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.
3.2.6. 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.
This build is not ABI compatible with release build (default build) or debug build (
Py_DEBUG
andPy_REF_DEBUG
macros).New in version 3.8.
- --with-assertions¶
Build with C assertions enabled (default is no):
assert(...);
and_PyObject_ASSERT(...);
.If set, the
NDEBUG
macro is not defined in theOPT
compiler variable.See also the
--with-pydebug
option (debug build) which also enables assertions.New 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.
New in version 3.6.
- --with-address-sanitizer¶
Enable AddressSanitizer memory error detector,
asan
(default is no).New in version 3.6.
- --with-memory-sanitizer¶
Enable MemorySanitizer allocation error detector,
msan
(default is no).New in version 3.6.
- --with-undefined-behavior-sanitizer¶
Enable UndefinedBehaviorSanitizer undefined behaviour detector,
ubsan
(default is no).New in version 3.6.
3.2.7. Linker options¶
Enable building a shared Python library:
libpython
(default is no).
- --without-static-libpython¶
Do not build
libpythonMAJOR.MINOR.a
and do not installpython.o
(built and enabled by default).New in version 3.10.
3.2.8. Libraries options¶
- --with-libs='lib1 ...'¶
Link against additional libraries (default is no).
- --with-system-expat¶
Build the
pyexpat
module using an installedexpat
library (default is no).
- --with-system-libmpdec¶
Build the
_decimal
extension module using an installedmpdec
library, see thedecimal
module (default is no).New in version 3.3.
- --with-readline=editline¶
Use
editline
library for backend of thereadline
module.Define the
WITH_EDITLINE
macro.New in version 3.10.
- --without-readline¶
Don’t build the
readline
module (built by default).Don’t define the
HAVE_LIBREADLINE
macro.New 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.
New 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
andpkg-config
;DIR: set an explicit rpath.
New in version 3.10.
3.2.9. Security Options¶
- --with-hash-algorithm=[fnv|siphash13|siphash24]¶
Select hash algorithm for use in
Python/pyhash.c
:siphash13
(default);siphash24
;fnv
.
New in version 3.4.
New 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
.
New 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.New in version 3.7.
Changed in version 3.10: The settings
python
and STRING also set TLS 1.2 as minimum protocol version.
3.2.10. 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
;32-bit
;64-bit
;3-way
;intel
;intel-32
;intel-64
;all
.
- --with-framework-name=FRAMEWORK¶
Specify the name for the python framework on macOS only valid when
--enable-framework
is set (default:Python
).
3.2.11. 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.
- --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 compilingNew in 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
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
3.3. Python Build System¶
3.3.1. Main files of the build system¶
configure.ac
=>configure
;Makefile.pre.in
=>Makefile
(created byconfigure
);pyconfig.h
(created byconfigure
);Modules/Setup
: C extensions built by the Makefile usingModule/makesetup
shell script;setup.py
: C extensions built using thesetuptools
package.
3.3.2. 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 staticlibpython
library are linked into the finalpython
program.C extensions are built by the Makefile (see
Modules/Setup
) andpython setup.py build
.
3.3.3. Main Makefile targets¶
make
: Build Python with the standard library.make platform:
: build thepython
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 themake
command (make all
or justmake
).make buildbottest
: Build Python and run the Python test suite, the same way than buildbots test Python. SetTESTTIMEOUT
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
andautoconf
must be run separately for the remaining generated files.make clean
: Remove built files.make distclean
: Same thanmake clean
, but remove also files created by the configure script.
3.3.4. 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 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 thePy_BUILD_CORE_MODULE
is definedUse
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.
3.4. Compiler and linker flags¶
Options set by the ./configure
script and environment variables and used by
Makefile
.
3.4.1. Preprocessor flags¶
- CONFIGURE_CPPFLAGS¶
Value of
CPPFLAGS
variable passed to the./configure
script.New in version 3.6.
- CPPFLAGS¶
(Objective) C/C++ preprocessor flags, e.g.
-I<include dir>
if you have headers in a nonstandard directory<include dir>
.Both
CPPFLAGS
andLDFLAGS
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.
- BASECPPFLAGS¶
New in version 3.4.
- PY_CPPFLAGS¶
Extra preprocessor flags added for building the interpreter object files.
Default:
$(BASECPPFLAGS) -I. -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS)
.New in version 3.2.
3.4.2. 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 the distutilsCFLAGS
once Python is installed (bpo-21121).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 inCFLAGS
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.
New in version 3.5.
- COMPILEALL_OPTS¶
Options passed to the
compileall
command line when building PYC files inmake install
. Default:-j0
.New in version 3.12.
- EXTRA_CFLAGS¶
Extra C compiler flags.
- CONFIGURE_CFLAGS_NODIST¶
Value of
CFLAGS_NODIST
variable passed to the./configure
script.New in version 3.5.
- BASECFLAGS¶
Base compiler flags.
- OPT¶
Optimization flags.
- CFLAGS_ALIASING¶
Strict or non-strict aliasing flags used to compile
Python/dtoa.c
.New in 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
.New in version 3.5.
- PY_STDMODULE_CFLAGS¶
C flags used for building the interpreter object files.
Default:
$(PY_CFLAGS) $(PY_CFLAGS_NODIST) $(PY_CPPFLAGS) $(CFLAGSFORSHARED)
.New in version 3.7.
- PY_CORE_CFLAGS¶
Default:
$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE
.New in 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
.New in version 3.8.
- PURIFY¶
Purify command. Purify is a memory debugger program.
Default: empty string (not used).
3.4.3. 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.New in version 3.2.
- LDFLAGS_NODIST¶
LDFLAGS_NODIST
is used in the same manner asCFLAGS_NODIST
. Use it when a linker flag should not be part of the distutilsLDFLAGS
once Python is installed (bpo-35257).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 inLDFLAGS
would take precedence over user- and package-supplied-L
flags.
- CONFIGURE_LDFLAGS_NODIST¶
Value of
LDFLAGS_NODIST
variable passed to the./configure
script.New in version 3.8.
- LDFLAGS¶
Linker flags, e.g.
-L<lib dir>
if you have libraries in a nonstandard directory<lib dir>
.Both
CPPFLAGS
andLDFLAGS
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.
- 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)
.New in version 3.8.
- PY_CORE_LDFLAGS¶
Linker flags used for building the interpreter object files.
New in version 3.8.