Python Initialization Configuration¶
Added in version 3.8.
Python can be initialized with Py_InitializeFromConfig() and the
PyConfig structure. It can be preinitialized with
Py_PreInitialize() and the PyPreConfig structure.
There are two kinds of configuration:
The Python Configuration can be used to build a customized Python which behaves as the regular Python. For example, environment variables and command line arguments are used to configure Python.
The Isolated Configuration can be used to embed Python into an application. It isolates Python from the system. For example, environment variables are ignored, the LC_CTYPE locale is left unchanged and no signal handler is registered.
The Py_RunMain() function can be used to write a customized Python
program.
See also Initialization, Finalization, and Threads.
See also
PEP 587 “Python Initialization Configuration”.
Example¶
Example of customized Python always running in isolated mode:
int main(int argc, char **argv)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
config.isolated = 1;
/* Decode command line arguments.
Implicitly preinitialize Python (in isolated mode). */
status = PyConfig_SetBytesArgv(&config, argc, argv);
if (PyStatus_Exception(status)) {
goto exception;
}
status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto exception;
}
PyConfig_Clear(&config);
return Py_RunMain();
exception:
PyConfig_Clear(&config);
if (PyStatus_IsExit(status)) {
return status.exitcode;
}
/* Display the error message and exit the process with
non-zero exit code */
Py_ExitStatusException(status);
}
PyWideStringList¶
-
type PyWideStringList¶
List of
wchar_t*strings.If length is non-zero, items must be non-
NULLand all strings must be non-NULL.Methods:
-
PyStatus PyWideStringList_Append(PyWideStringList *list, const wchar_t *item)¶
Append item to list.
Python must be preinitialized to call this function.
-
PyStatus PyWideStringList_Insert(PyWideStringList *list, Py_ssize_t index, const wchar_t *item)¶
Insert item into list at index.
If index is greater than or equal to list length, append item to list.
index must be greater than or equal to
0.Python must be preinitialized to call this function.
Structure fields:
-
Py_ssize_t length¶
List length.
-
wchar_t **items¶
List items.
-
PyStatus PyWideStringList_Append(PyWideStringList *list, const wchar_t *item)¶
PyStatus¶
-
type PyStatus¶
Structure to store an initialization function status: success, error or exit.
For an error, it can store the C function name which created the error.
Structure fields:
-
int exitcode¶
Exit code. Argument passed to
exit().
-
const char *err_msg¶
Error message.
-
const char *func¶
Name of the function which created an error, can be
NULL.
Functions to create a status:
-
PyStatus PyStatus_Error(const char *err_msg)¶
Initialization error with a message.
err_msg must not be
NULL.
Functions to handle a status:
-
int PyStatus_Exception(PyStatus status)¶
Is the status an error or an exit? If true, the exception must be handled; by calling
Py_ExitStatusException()for example.
-
int exitcode¶
Note
Internally, Python uses macros which set PyStatus.func,
whereas functions to create a status set func to NULL.
Example:
PyStatus alloc(void **ptr, size_t size)
{
*ptr = PyMem_RawMalloc(size);
if (*ptr == NULL) {
return PyStatus_NoMemory();
}
return PyStatus_Ok();
}
int main(int argc, char **argv)
{
void *ptr;
PyStatus status = alloc(&ptr, 16);
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
PyMem_Free(ptr);
return 0;
}
PyPreConfig¶
-
type PyPreConfig¶
Structure used to preinitialize Python.
Function to initialize a preconfiguration:
-
void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)¶
Initialize the preconfiguration with Python Configuration.
-
void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)¶
Initialize the preconfiguration with Isolated Configuration.
Structure fields:
-
int allocator¶
Name of the Python memory allocators:
PYMEM_ALLOCATOR_NOT_SET(0): don’t change memory allocators (use defaults).PYMEM_ALLOCATOR_DEFAULT(1): default memory allocators.PYMEM_ALLOCATOR_DEBUG(2): default memory allocators with debug hooks.PYMEM_ALLOCATOR_MALLOC(3): usemalloc()of the C library.PYMEM_ALLOCATOR_MALLOC_DEBUG(4): force usage ofmalloc()with debug hooks.PYMEM_ALLOCATOR_PYMALLOC(5): Python pymalloc memory allocator.PYMEM_ALLOCATOR_PYMALLOC_DEBUG(6): Python pymalloc memory allocator with debug hooks.PYMEM_ALLOCATOR_MIMALLOC(6): usemimalloc, a fast malloc replacement.PYMEM_ALLOCATOR_MIMALLOC_DEBUG(7): usemimalloc, a fast malloc replacement with debug hooks.
PYMEM_ALLOCATOR_PYMALLOCandPYMEM_ALLOCATOR_PYMALLOC_DEBUGare not supported if Python isconfigured using --without-pymalloc.PYMEM_ALLOCATOR_MIMALLOCandPYMEM_ALLOCATOR_MIMALLOC_DEBUGare not supported if Python isconfigured using --without-mimallocor if the underlying atomic support isn’t available.See Memory Management.
Default:
PYMEM_ALLOCATOR_NOT_SET.
-
int configure_locale¶
Set the LC_CTYPE locale to the user preferred locale.
If equals to
0, setcoerce_c_localeandcoerce_c_locale_warnmembers to0.See the locale encoding.
Default:
1in Python config,0in isolated config.
-
int coerce_c_locale¶
If equals to
2, coerce the C locale.If equals to
1, read the LC_CTYPE locale to decide if it should be coerced.See the locale encoding.
Default:
-1in Python config,0in isolated config.
-
int coerce_c_locale_warn¶
If non-zero, emit a warning if the C locale is coerced.
Default:
-1in Python config,0in isolated config.
-
int dev_mode¶
Python Development Mode: see
PyConfig.dev_mode.Default:
-1in Python mode,0in isolated mode.
-
int isolated¶
Isolated mode: see
PyConfig.isolated.Default:
0in Python mode,1in isolated mode.
-
int legacy_windows_fs_encoding¶
If non-zero:
Set
PyPreConfig.utf8_modeto0,Set
PyConfig.filesystem_encodingto"mbcs",Set
PyConfig.filesystem_errorsto"replace".
Initialized from the
PYTHONLEGACYWINDOWSFSENCODINGenvironment variable value.Only available on Windows.
#ifdef MS_WINDOWSmacro can be used for Windows specific code.Default:
0.
-
int parse_argv¶
If non-zero,
Py_PreInitializeFromArgs()andPy_PreInitializeFromBytesArgs()parse theirargvargument the same way the regular Python parses command line arguments: see Command Line Arguments.Default:
1in Python config,0in isolated config.
-
int use_environment¶
Use environment variables? See
PyConfig.use_environment.Default:
1in Python config and0in isolated config.
-
int utf8_mode¶
If non-zero, enable the Python UTF-8 Mode.
Set to
0or1by the-X utf8command line option and thePYTHONUTF8environment variable.Also set to
1if theLC_CTYPElocale isCorPOSIX.Default:
-1in Python config and0in isolated config.
-
void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)¶
Preinitialize Python with PyPreConfig¶
The preinitialization of Python:
Set the Python memory allocators (
PyPreConfig.allocator)Configure the LC_CTYPE locale (locale encoding)
Set the Python UTF-8 Mode (
PyPreConfig.utf8_mode)
The current preconfiguration (PyPreConfig type) is stored in
_PyRuntime.preconfig.
Functions to preinitialize Python:
-
PyStatus Py_PreInitialize(const PyPreConfig *preconfig)¶
Preinitialize Python from preconfig preconfiguration.
preconfig must not be
NULL.
-
PyStatus Py_PreInitializeFromBytesArgs(const PyPreConfig *preconfig, int argc, char *const *argv)¶
Preinitialize Python from preconfig preconfiguration.
Parse argv command line arguments (bytes strings) if
parse_argvof preconfig is non-zero.preconfig must not be
NULL.
-
PyStatus Py_PreInitializeFromArgs(const PyPreConfig *preconfig, int argc, wchar_t *const *argv)¶
Preinitialize Python from preconfig preconfiguration.
Parse argv command line arguments (wide strings) if
parse_argvof preconfig is non-zero.preconfig must not be
NULL.
The caller is responsible to handle exceptions (error or exit) using
PyStatus_Exception() and Py_ExitStatusException().
For Python Configuration
(PyPreConfig_InitPythonConfig()), if Python is initialized with
command line arguments, the command line arguments must also be passed to
preinitialize Python, since they have an effect on the pre-configuration
like encodings. For example, the -X utf8 command line option
enables the Python UTF-8 Mode.
PyMem_SetAllocator() can be called after Py_PreInitialize() and
before Py_InitializeFromConfig() to install a custom memory allocator.
It can be called before Py_PreInitialize() if
PyPreConfig.allocator is set to PYMEM_ALLOCATOR_NOT_SET.
Python memory allocation functions like PyMem_RawMalloc() must not be
used before the Python preinitialization, whereas calling directly malloc()
and free() is always safe. Py_DecodeLocale() must not be called
before the Python preinitialization.
Example using the preinitialization to enable the Python UTF-8 Mode:
PyStatus status;
PyPreConfig preconfig;
PyPreConfig_InitPythonConfig(&preconfig);
preconfig.utf8_mode = 1;
status = Py_PreInitialize(&preconfig);
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
/* at this point, Python speaks UTF-8 */
Py_Initialize();
/* ... use Python API here ... */
Py_Finalize();
PyConfig¶
-
type PyConfig¶
Structure containing most parameters to configure Python.
When done, the
PyConfig_Clear()function must be used to release the configuration memory.Structure methods:
-
void PyConfig_InitPythonConfig(PyConfig *config)¶
Initialize configuration with the Python Configuration.
-
void PyConfig_InitIsolatedConfig(PyConfig *config)¶
Initialize configuration with the Isolated Configuration.
-
PyStatus PyConfig_SetString(PyConfig *config, wchar_t *const *config_str, const wchar_t *str)¶
Copy the wide character string str into
*config_str.Preinitialize Python if needed.
-
PyStatus PyConfig_SetBytesString(PyConfig *config, wchar_t *const *config_str, const char *str)¶
Decode str using
Py_DecodeLocale()and set the result into*config_str.Preinitialize Python if needed.
-
PyStatus PyConfig_SetArgv(PyConfig *config, int argc, wchar_t *const *argv)¶
Set command line arguments (
argvmember of config) from the argv list of wide character strings.Preinitialize Python if needed.
-
PyStatus PyConfig_SetBytesArgv(PyConfig *config, int argc, char *const *argv)¶
Set command line arguments (
argvmember of config) from the argv list of bytes strings. Decode bytes usingPy_DecodeLocale().Preinitialize Python if needed.
-
PyStatus PyConfig_SetWideStringList(PyConfig *config, PyWideStringList *list, Py_ssize_t length, wchar_t **items)¶
Set the list of wide strings list to length and items.
Preinitialize Python if needed.
-
PyStatus PyConfig_Read(PyConfig *config)¶
Read all Python configuration.
Fields which are already initialized are left unchanged.
Fields for path configuration are no longer calculated or modified when calling this function, as of Python 3.11.
The
PyConfig_Read()function only parsesPyConfig.argvarguments once:PyConfig.parse_argvis set to2after arguments are parsed. Since Python arguments are stripped fromPyConfig.argv, parsing arguments twice would parse the application options as Python options.Preinitialize Python if needed.
Changed in version 3.10: The
PyConfig.argvarguments are now only parsed once,PyConfig.parse_argvis set to2after arguments are parsed, and arguments are only parsed ifPyConfig.parse_argvequals1.Changed in version 3.11:
PyConfig_Read()no longer calculates all paths, and so fields listed under Python Path Configuration may no longer be updated untilPy_InitializeFromConfig()is called.
Most
PyConfigmethods preinitialize Python if needed. In that case, the Python preinitialization configuration (PyPreConfig) in based on thePyConfig. If configuration fields which are in common withPyPreConfigare tuned, they must be set before calling aPyConfigmethod:Moreover, if
PyConfig_SetArgv()orPyConfig_SetBytesArgv()is used, this method must be called before other methods, since the preinitialization configuration depends on command line arguments (ifparse_argvis non-zero).The caller of these methods is responsible to handle exceptions (error or exit) using
PyStatus_Exception()andPy_ExitStatusException().Structure fields:
-
PyWideStringList argv¶
Set
sys.argvcommand line arguments based onargv. These parameters are similar to those passed to the program’smain()function with the difference that the first entry should refer to the script file to be executed rather than the executable hosting the Python interpreter. If there isn’t a script that will be run, the first entry inargvcan be an empty string.Set
parse_argvto1to parseargvthe same way the regular Python parses Python command line arguments and then to strip Python arguments fromargv.If
argvis empty, an empty string is added to ensure thatsys.argvalways exists and is never empty.Default:
NULL.See also the
orig_argvmember.
-
int safe_path¶
If equals to zero,
Py_RunMain()prepends a potentially unsafe path tosys.pathat startup:If
argv[0]is equal toL"-m"(python -m module), prepend the current working directory.If running a script (
python script.py), prepend the script’s directory. If it’s a symbolic link, resolve symbolic links.Otherwise (
python -c codeandpython), prepend an empty string, which means the current working directory.
Set to
1by the-Pcommand line option and thePYTHONSAFEPATHenvironment variable.Default:
0in Python config,1in isolated config.Added in version 3.11.
-
wchar_t *base_exec_prefix¶
-
Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.exec_prefix.
-
wchar_t *base_executable¶
Python base executable:
sys._base_executable.Set by the
__PYVENV_LAUNCHER__environment variable.Set from
PyConfig.executableifNULL.Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.executable.
-
wchar_t *base_prefix¶
-
Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.prefix.
-
int buffered_stdio¶
If equals to
0andconfigure_c_stdiois non-zero, disable buffering on the C streams stdout and stderr.Set to
0by the-ucommand line option and thePYTHONUNBUFFEREDenvironment variable.stdin is always opened in buffered mode.
Default:
1.
-
int bytes_warning¶
If equals to
1, issue a warning when comparingbytesorbytearraywithstr, or comparingbyteswithint.If equal or greater to
2, raise aBytesWarningexception in these cases.Incremented by the
-bcommand line option.Default:
0.
-
int warn_default_encoding¶
If non-zero, emit a
EncodingWarningwarning whenio.TextIOWrapperuses its default encoding. See Opt-in EncodingWarning for details.Default:
0.Added in version 3.10.
-
int code_debug_ranges¶
If equals to
0, disables the inclusion of the end line and column mappings in code objects. Also disables traceback printing carets to specific error locations.Set to
0by thePYTHONNODEBUGRANGESenvironment variable and by the-X no_debug_rangescommand line option.Default:
1.Added in version 3.11.
-
wchar_t *check_hash_pycs_mode¶
Control the validation behavior of hash-based
.pycfiles: value of the--check-hash-based-pycscommand line option.Valid values:
L"always": Hash the source file for invalidation regardless of value of the ‘check_source’ flag.L"never": Assume that hash-based pycs always are valid.L"default": The ‘check_source’ flag in hash-based pycs determines invalidation.
Default:
L"default".See also PEP 552 “Deterministic pycs”.
-
int configure_c_stdio¶
If non-zero, configure C standard streams:
On Windows, set the binary mode (
O_BINARY) on stdin, stdout and stderr.If
buffered_stdioequals zero, disable buffering of stdin, stdout and stderr streams.If
interactiveis non-zero, enable stream buffering on stdin and stdout (only stdout on Windows).
Default:
1in Python config,0in isolated config.
-
int dev_mode¶
If non-zero, enable the Python Development Mode.
Set to
1by the-X devoption and thePYTHONDEVMODEenvironment variable.Default:
-1in Python mode,0in isolated mode.
-
int dump_refs¶
Dump Python references?
If non-zero, dump all objects which are still alive at exit.
Set to
1by thePYTHONDUMPREFSenvironment variable.Needs a special build of Python with the
Py_TRACE_REFSmacro defined: see theconfigure --with-trace-refs option.Default:
0.
-
wchar_t *exec_prefix¶
The site-specific directory prefix where the platform-dependent Python files are installed:
sys.exec_prefix.Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.base_exec_prefix.
-
wchar_t *executable¶
The absolute path of the executable binary for the Python interpreter:
sys.executable.Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.base_executable.
-
int faulthandler¶
Enable faulthandler?
If non-zero, call
faulthandler.enable()at startup.Set to
1by-X faulthandlerand thePYTHONFAULTHANDLERenvironment variable.Default:
-1in Python mode,0in isolated mode.
-
wchar_t *filesystem_encoding¶
Filesystem encoding:
sys.getfilesystemencoding().On macOS, Android and VxWorks: use
"utf-8"by default.On Windows: use
"utf-8"by default, or"mbcs"iflegacy_windows_fs_encodingofPyPreConfigis non-zero.Default encoding on other platforms:
"utf-8"ifPyPreConfig.utf8_modeis non-zero."ascii"if Python detects thatnl_langinfo(CODESET)announces the ASCII encoding, whereas thembstowcs()function decodes from a different encoding (usually Latin1)."utf-8"ifnl_langinfo(CODESET)returns an empty string.Otherwise, use the locale encoding:
nl_langinfo(CODESET)result.
At Python startup, the encoding name is normalized to the Python codec name. For example,
"ANSI_X3.4-1968"is replaced with"ascii".See also the
filesystem_errorsmember.
-
wchar_t *filesystem_errors¶
Filesystem error handler:
sys.getfilesystemencodeerrors().On Windows: use
"surrogatepass"by default, or"replace"iflegacy_windows_fs_encodingofPyPreConfigis non-zero.On other platforms: use
"surrogateescape"by default.Supported error handlers:
"strict""surrogateescape""surrogatepass"(only supported with the UTF-8 encoding)
See also the
filesystem_encodingmember.
-
unsigned long hash_seed¶
-
int use_hash_seed¶
Randomized hash function seed.
If
use_hash_seedis zero, a seed is chosen randomly at Python startup, andhash_seedis ignored.Set by the
PYTHONHASHSEEDenvironment variable.Default use_hash_seed value:
-1in Python mode,0in isolated mode.
-
wchar_t *home¶
Set the default Python “home” directory, that is, the location of the standard Python libraries (see
PYTHONHOME).Set by the
PYTHONHOMEenvironment variable.Default:
NULL.Part of the Python Path Configuration input.
-
int import_time¶
If non-zero, profile import time.
Set the
1by the-X importtimeoption and thePYTHONPROFILEIMPORTTIMEenvironment variable.Default:
0.
-
int inspect¶
Enter interactive mode after executing a script or a command.
If greater than
0, enable inspect: when a script is passed as first argument or the -c option is used, enter interactive mode after executing the script or the command, even whensys.stdindoes not appear to be a terminal.Incremented by the
-icommand line option. Set to1if thePYTHONINSPECTenvironment variable is non-empty.Default:
0.
-
int install_signal_handlers¶
Install Python signal handlers?
Default:
1in Python mode,0in isolated mode.
-
int interactive¶
If greater than
0, enable the interactive mode (REPL).Incremented by the
-icommand line option.Default:
0.
-
int int_max_str_digits¶
Configures the integer string conversion length limitation. An initial value of
-1means the value will be taken from the command line or environment or otherwise default to 4300 (sys.int_info.default_max_str_digits). A value of0disables the limitation. Values greater than zero but less than 640 (sys.int_info.str_digits_check_threshold) are unsupported and will produce an error.Configured by the
-X int_max_str_digitscommand line flag or thePYTHONINTMAXSTRDIGITSenvironment variable.Default:
-1in Python mode. 4300 (sys.int_info.default_max_str_digits) in isolated mode.Added in version 3.12.
-
int cpu_count¶
If the value of
cpu_countis not-1then it will override the return values ofos.cpu_count(),os.process_cpu_count(), andmultiprocessing.cpu_count().Configured by the
-X cpu_count=n|defaultcommand line flag or thePYTHON_CPU_COUNTenvironment variable.Default:
-1.Added in version 3.13.
-
int isolated¶
If greater than
0, enable isolated mode:Set
safe_pathto1: don’t prepend a potentially unsafe path tosys.pathat Python startup, such as the current directory, the script’s directory or an empty string.Set
use_environmentto0: ignorePYTHONenvironment variables.Set
user_site_directoryto0: don’t add the user site directory tosys.path.Python REPL doesn’t import
readlinenor enable default readline configuration on interactive prompts.
Set to
1by the-Icommand line option.Default:
0in Python mode,1in isolated mode.See also the Isolated Configuration and
PyPreConfig.isolated.
-
int legacy_windows_stdio¶
If non-zero, use
io.FileIOinstead ofio._WindowsConsoleIOforsys.stdin,sys.stdoutandsys.stderr.Set to
1if thePYTHONLEGACYWINDOWSSTDIOenvironment variable is set to a non-empty string.Only available on Windows.
#ifdef MS_WINDOWSmacro can be used for Windows specific code.Default:
0.See also the PEP 528 (Change Windows console encoding to UTF-8).
-
int malloc_stats¶
If non-zero, dump statistics on Python pymalloc memory allocator at exit.
Set to
1by thePYTHONMALLOCSTATSenvironment variable.The option is ignored if Python is
configured using the --without-pymalloc option.Default:
0.
-
wchar_t *platlibdir¶
Platform library directory name:
sys.platlibdir.Set by the
PYTHONPLATLIBDIRenvironment variable.Default: value of the
PLATLIBDIRmacro which is set by theconfigure --with-platlibdir option(default:"lib", or"DLLs"on Windows).Part of the Python Path Configuration input.
Added in version 3.9.
Changed in version 3.11: This macro is now used on Windows to locate the standard library extension modules, typically under
DLLs. However, for compatibility, note that this value is ignored for any non-standard layouts, including in-tree builds and virtual environments.
-
wchar_t *pythonpath_env¶
Module search paths (
sys.path) as a string separated byDELIM(os.pathsep).Set by the
PYTHONPATHenvironment variable.Default:
NULL.Part of the Python Path Configuration input.
-
PyWideStringList module_search_paths¶
-
int module_search_paths_set¶
Module search paths:
sys.path.If
module_search_paths_setis equal to0,Py_InitializeFromConfig()will replacemodule_search_pathsand setsmodule_search_paths_setto1.Default: empty list (
module_search_paths) and0(module_search_paths_set).Part of the Python Path Configuration output.
-
int optimization_level¶
Compilation optimization level:
0: Peephole optimizer, set__debug__toTrue.1: Level 0, remove assertions, set__debug__toFalse.2: Level 1, strip docstrings.
Incremented by the
-Ocommand line option. Set to thePYTHONOPTIMIZEenvironment variable value.Default:
0.
-
PyWideStringList orig_argv¶
The list of the original command line arguments passed to the Python executable:
sys.orig_argv.If
orig_argvlist is empty andargvis not a list only containing an empty string,PyConfig_Read()copiesargvintoorig_argvbefore modifyingargv(ifparse_argvis non-zero).See also the
argvmember and thePy_GetArgcArgv()function.Default: empty list.
Added in version 3.10.
-
int parse_argv¶
Parse command line arguments?
If equals to
1, parseargvthe same way the regular Python parses command line arguments, and strip Python arguments fromargv.The
PyConfig_Read()function only parsesPyConfig.argvarguments once:PyConfig.parse_argvis set to2after arguments are parsed. Since Python arguments are stripped fromPyConfig.argv, parsing arguments twice would parse the application options as Python options.Default:
1in Python mode,0in isolated mode.Changed in version 3.10: The
PyConfig.argvarguments are now only parsed ifPyConfig.parse_argvequals to1.
-
int parser_debug¶
Parser debug mode. If greater than
0, turn on parser debugging output (for expert only, depending on compilation options).Incremented by the
-dcommand line option. Set to thePYTHONDEBUGenvironment variable value.Needs a debug build of Python (the
Py_DEBUGmacro must be defined).Default:
0.
-
int pathconfig_warnings¶
If non-zero, calculation of path configuration is allowed to log warnings into
stderr. If equals to0, suppress these warnings.Default:
1in Python mode,0in isolated mode.Part of the Python Path Configuration input.
Changed in version 3.11: Now also applies on Windows.
-
wchar_t *prefix¶
The site-specific directory prefix where the platform independent Python files are installed:
sys.prefix.Default:
NULL.Part of the Python Path Configuration output.
See also
PyConfig.base_prefix.
-
wchar_t *program_name¶
Program name used to initialize
executableand in early error messages during Python initialization.On macOS, use
PYTHONEXECUTABLEenvironment variable if set.If the
WITH_NEXT_FRAMEWORKmacro is defined, use__PYVENV_LAUNCHER__environment variable if set.Use
argv[0]ofargvif available and non-empty.Otherwise, use
L"python"on Windows, orL"python3"on other platforms.
Default:
NULL.Part of the Python Path Configuration input.
-
wchar_t *pycache_prefix¶
Directory where cached
.pycfiles are written:sys.pycache_prefix.Set by the
-X pycache_prefix=PATHcommand line option and thePYTHONPYCACHEPREFIXenvironment variable. The command-line option takes precedence.If
NULL,sys.pycache_prefixis set toNone.Default:
NULL.
-
int quiet¶
Quiet mode. If greater than
0, don’t display the copyright and version at Python startup in interactive mode.Incremented by the
-qcommand line option.Default:
0.
-
wchar_t *run_command¶
Value of the
-ccommand line option.Used by
Py_RunMain().Default:
NULL.
-
wchar_t *run_filename¶
Filename passed on the command line: trailing command line argument without
-cor-m. It is used by thePy_RunMain()function.For example, it is set to
script.pyby thepython3 script.py argcommand line.See also the
PyConfig.skip_source_first_lineoption.Default:
NULL.
-
wchar_t *run_module¶
Value of the
-mcommand line option.Used by
Py_RunMain().Default:
NULL.
-
wchar_t *run_presite¶
package.modulepath to module that should be imported beforesite.pyis run.Set by the
-X presite=package.modulecommand-line option and thePYTHON_PRESITEenvironment variable. The command-line option takes precedence.Needs a debug build of Python (the
Py_DEBUGmacro must be defined).Default:
NULL.
-
int show_ref_count¶
Show total reference count at exit (excluding immortal objects)?
Set to
1by-X showrefcountcommand line option.Needs a debug build of Python (the
Py_REF_DEBUGmacro must be defined).Default:
0.
-
int site_import¶
Import the
sitemodule at startup?If equal to zero, disable the import of the module site and the site-dependent manipulations of
sys.paththat it entails.Also disable these manipulations if the
sitemodule is explicitly imported later (callsite.main()if you want them to be triggered).Set to
0by the-Scommand line option.sys.flags.no_siteis set to the inverted value ofsite_import.Default:
1.
-
int skip_source_first_line¶
If non-zero, skip the first line of the
PyConfig.run_filenamesource.It allows the usage of non-Unix forms of
#!cmd. This is intended for a DOS specific hack only.Set to
1by the-xcommand line option.Default:
0.
-
wchar_t *stdio_encoding¶
-
wchar_t *stdio_errors¶
Encoding and encoding errors of
sys.stdin,sys.stdoutandsys.stderr(butsys.stderralways uses"backslashreplace"error handler).Use the
PYTHONIOENCODINGenvironment variable if it is non-empty.Default encoding:
"UTF-8"ifPyPreConfig.utf8_modeis non-zero.Otherwise, use the locale encoding.
Default error handler:
On Windows: use
"surrogateescape"."surrogateescape"ifPyPreConfig.utf8_modeis non-zero, or if the LC_CTYPE locale is “C” or “POSIX”."strict"otherwise.
See also
PyConfig.legacy_windows_stdio.
-
int tracemalloc¶
Enable tracemalloc?
If non-zero, call
tracemalloc.start()at startup.Set by
-X tracemalloc=Ncommand line option and by thePYTHONTRACEMALLOCenvironment variable.Default:
-1in Python mode,0in isolated mode.
-
int perf_profiling¶
Enable compatibility mode with the perf profiler?
If non-zero, initialize the perf trampoline. See Python support for the Linux perf profiler for more information.
Set by
-X perfcommand-line option and by thePYTHON_PERF_JIT_SUPPORTenvironment variable for perf support with stack pointers and-X perf_jitcommand-line option and by thePYTHON_PERF_JIT_SUPPORTenvironment variable for perf support with DWARF JIT information.Default:
-1.Added in version 3.12.
-
int use_environment¶
-
If equals to zero, ignore the environment variables.
Set to
0by the-Eenvironment variable.Default:
1in Python config and0in isolated config.
-
int use_system_logger¶
If non-zero,
stdoutandstderrwill be redirected to the system log.Only available on macOS 10.12 and later, and on iOS.
Default:
0(don’t use system log).Added in version 3.13.2.
-
int user_site_directory¶
If non-zero, add the user site directory to
sys.path.Set to
0by the-sand-Icommand line options.Set to
0by thePYTHONNOUSERSITEenvironment variable.Default:
1in Python mode,0in isolated mode.
-
int verbose¶
Verbose mode. If greater than
0, print a message each time a module is imported, showing the place (filename or built-in module) from which it is loaded.If greater than or equal to
2, print a message for each file that is checked for when searching for a module. Also provides information on module cleanup at exit.Incremented by the
-vcommand line option.Set by the
PYTHONVERBOSEenvironment variable value.Default:
0.
-
PyWideStringList warnoptions¶
Options of the
warningsmodule to build warnings filters, lowest to highest priority:sys.warnoptions.The
warningsmodule addssys.warnoptionsin the reverse order: the lastPyConfig.warnoptionsitem becomes the first item ofwarnings.filterswhich is checked first (highest priority).The
-Wcommand line options adds its value towarnoptions, it can be used multiple times.The
PYTHONWARNINGSenvironment variable can also be used to add warning options. Multiple options can be specified, separated by commas (,).Default: empty list.
-
int write_bytecode¶
If equal to
0, Python won’t try to write.pycfiles on the import of source modules.Set to
0by the-Bcommand line option and thePYTHONDONTWRITEBYTECODEenvironment variable.sys.dont_write_bytecodeis initialized to the inverted value ofwrite_bytecode.Default:
1.
-
PyWideStringList xoptions¶
Values of the
-Xcommand line options:sys._xoptions.Default: empty list.
-
void PyConfig_InitPythonConfig(PyConfig *config)¶
If parse_argv is non-zero, argv
arguments are parsed the same way the regular Python parses command line
arguments, and Python arguments are stripped from
argv.
The xoptions options are parsed to set other options: see
the -X command line option.
Changed in version 3.9: The show_alloc_count field has been removed.
Initialization with PyConfig¶
Initializing the interpreter from a populated configuration struct is handled
by calling Py_InitializeFromConfig().
The caller is responsible to handle exceptions (error or exit) using
PyStatus_Exception() and Py_ExitStatusException().
If PyImport_FrozenModules(), PyImport_AppendInittab() or
PyImport_ExtendInittab() are used, they must be set or called after
Python preinitialization and before the Python initialization. If Python is
initialized multiple times, PyImport_AppendInittab() or
PyImport_ExtendInittab() must be called before each Python
initialization.
The current configuration (PyConfig type) is stored in
PyInterpreterState.config.
Example setting the program name:
void init_python(void)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
/* Set the program name. Implicitly preinitialize Python. */
status = PyConfig_SetString(&config, &config.program_name,
L"/path/to/my_program");
if (PyStatus_Exception(status)) {
goto exception;
}
status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto exception;
}
PyConfig_Clear(&config);
return;
exception:
PyConfig_Clear(&config);
Py_ExitStatusException(status);
}
More complete example modifying the default configuration, read the configuration, and then override some parameters. Note that since 3.11, many parameters are not calculated until initialization, and so values cannot be read from the configuration structure. Any values set before initialize is called will be left unchanged by initialization:
PyStatus init_python(const char *program_name)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
/* Set the program name before reading the configuration
(decode byte string from the locale encoding).
Implicitly preinitialize Python. */
status = PyConfig_SetBytesString(&config, &config.program_name,
program_name);
if (PyStatus_Exception(status)) {
goto done;
}
/* Read all configuration at once */
status = PyConfig_Read(&config);
if (PyStatus_Exception(status)) {
goto done;
}
/* Specify sys.path explicitly */
/* If you want to modify the default set of paths, finish
initialization first and then use PySys_GetObject("path") */
config.module_search_paths_set = 1;
status = PyWideStringList_Append(&config.module_search_paths,
L"/path/to/stdlib");
if (PyStatus_Exception(status)) {
goto done;
}
status = PyWideStringList_Append(&config.module_search_paths,
L"/path/to/more/modules");
if (PyStatus_Exception(status)) {
goto done;
}
/* Override executable computed by PyConfig_Read() */
status = PyConfig_SetString(&config, &config.executable,
L"/path/to/my_executable");
if (PyStatus_Exception(status)) {
goto done;
}
status = Py_InitializeFromConfig(&config);
done:
PyConfig_Clear(&config);
return status;
}
Isolated Configuration¶
PyPreConfig_InitIsolatedConfig() and
PyConfig_InitIsolatedConfig() functions create a configuration to
isolate Python from the system. For example, to embed Python into an
application.
This configuration ignores global configuration variables, environment
variables, command line arguments (PyConfig.argv is not parsed)
and user site directory. The C standard streams (ex: stdout) and the
LC_CTYPE locale are left unchanged. Signal handlers are not installed.
Configuration files are still used with this configuration to determine
paths that are unspecified. Ensure PyConfig.home is specified
to avoid computing the default path configuration.
Python Configuration¶
PyPreConfig_InitPythonConfig() and PyConfig_InitPythonConfig()
functions create a configuration to build a customized Python which behaves as
the regular Python.
Environments variables and command line arguments are used to configure Python, whereas global configuration variables are ignored.
This function enables C locale coercion (PEP 538)
and Python UTF-8 Mode
(PEP 540) depending on the LC_CTYPE locale, PYTHONUTF8 and
PYTHONCOERCECLOCALE environment variables.
Python Path Configuration¶
PyConfig contains multiple fields for the path configuration:
Path configuration inputs:
current working directory: to get absolute paths
PATHenvironment variable to get the program full path (fromPyConfig.program_name)__PYVENV_LAUNCHER__environment variable(Windows only) Application paths in the registry under “SoftwarePythonPythonCoreX.YPythonPath” of HKEY_CURRENT_USER and HKEY_LOCAL_MACHINE (where X.Y is the Python version).
Path configuration output fields:
If at least one “output field” is not set, Python calculates the path
configuration to fill unset fields. If
module_search_paths_set is equal to 0,
module_search_paths is overridden and
module_search_paths_set is set to 1.
It is possible to completely ignore the function calculating the default
path configuration by setting explicitly all path configuration output
fields listed above. A string is considered as set even if it is non-empty.
module_search_paths is considered as set if
module_search_paths_set is set to 1. In this case,
module_search_paths will be used without modification.
Set pathconfig_warnings to 0 to suppress warnings when
calculating the path configuration (Unix only, Windows does not log any warning).
If base_prefix or base_exec_prefix
fields are not set, they inherit their value from prefix
and exec_prefix respectively.
Py_RunMain() and Py_Main() modify sys.path:
If
run_filenameis set and is a directory which contains a__main__.pyscript, prependrun_filenametosys.path.If
isolatedis zero:If
run_moduleis set, prepend the current directory tosys.path. Do nothing if the current directory cannot be read.If
run_filenameis set, prepend the directory of the filename tosys.path.Otherwise, prepend an empty string to
sys.path.
If site_import is non-zero, sys.path can be
modified by the site module. If
user_site_directory is non-zero and the user’s
site-package directory exists, the site module appends the user’s
site-package directory to sys.path.
The following configuration files are used by the path configuration:
pyvenv.cfg._pthfile (ex:python._pth)pybuilddir.txt(Unix only)
If a ._pth file is present:
Set
isolatedto1.Set
use_environmentto0.Set
site_importto0.Set
safe_pathto1.
The __PYVENV_LAUNCHER__ environment variable is used to set
PyConfig.base_executable.
Py_GetArgcArgv()¶
-
void Py_GetArgcArgv(int *argc, wchar_t ***argv)¶
Get the original command line arguments, before Python modified them.
See also
PyConfig.orig_argvmember.
Multi-Phase Initialization Private Provisional API¶
This section is a private provisional API introducing multi-phase initialization, the core feature of PEP 432:
“Core” initialization phase, “bare minimum Python”:
“Main” initialization phase, Python is fully initialized:
Install and configure
importlib;Apply the Path Configuration;
Install signal handlers;
Finish
sysmodule initialization (ex: createsys.stdoutandsys.path);Enable optional features like
faulthandlerandtracemalloc;Import the
sitemodule;etc.
Private provisional API:
PyConfig._init_main: if set to0,Py_InitializeFromConfig()stops at the “Core” initialization phase.
-
PyStatus _Py_InitializeMain(void)¶
Move to the “Main” initialization phase, finish the Python initialization.
No module is imported during the “Core” phase and the importlib module is
not configured: the Path Configuration is only
applied during the “Main” phase. It may allow to customize Python in Python to
override or tune the Path Configuration, maybe
install a custom sys.meta_path importer or an import hook, etc.
It may become possible to calculate the Path Configuration in Python, after the Core phase and before the Main phase, which is one of the PEP 432 motivation.
The “Core” phase is not properly defined: what should be and what should not be available at this phase is not specified yet. The API is marked as private and provisional: the API can be modified or even be removed anytime until a proper public API is designed.
Example running Python code between “Core” and “Main” initialization phases:
void init_python(void)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
config._init_main = 0;
/* ... customize 'config' configuration ... */
status = Py_InitializeFromConfig(&config);
PyConfig_Clear(&config);
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
/* Use sys.stderr because sys.stdout is only created
by _Py_InitializeMain() */
int res = PyRun_SimpleString(
"import sys; "
"print('Run Python code before _Py_InitializeMain', "
"file=sys.stderr)");
if (res < 0) {
exit(1);
}
/* ... put more configuration code here ... */
status = _Py_InitializeMain();
if (PyStatus_Exception(status)) {
Py_ExitStatusException(status);
}
}