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Top Links: >> 80. Technology >> Internet Technology Summit Program >> 9. AI with Python >> 9.1. The Python Tutorial Introduction >> 9.1.1. Python Docs, Lexicon, and Components >> 9.1.1.2. Python Lexicon and Components
Current Topic: 9.1.1.2.16. Python Initialization Configuration
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New in version 3.8.



Structures:



Functions:



The preconfiguration (PyPreConfig type) is stored in _PyRuntime.preconfig and the configuration (PyConfig type) is stored in PyInterpreterState.config.


See also Initialization, Finalization, and Threads.



See also


PEP 587 ?Python Initialization Configuration?.




PyWideStringList




PyWideStringList



List of wchar_t* strings.


If length is non-zero, items must be non-NULL and 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




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_Ok
(void
)



Success.






PyStatus
PyStatus_Error
(const char
 *err_msg
)



Initialization error with a message.






PyStatus
PyStatus_NoMemory
(void
)



Memory allocation failure (out of memory).






PyStatus
PyStatus_Exit
(int
 exitcode
)



Exit Python with the specified exit code.




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
PyStatus_IsError
(
PyStatus
 status
)



Is the result an error?






int
PyStatus_IsExit
(
PyStatus
 status
)



Is the result an exit?






void
Py_ExitStatusException
(
PyStatus
 status
)



Call exit(exitcode) if status is an exit. Print the error message and exit with a non-zero exit code if status is an error. Must only be called if PyStatus_Exception(status) is non-zero.







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




PyPreConfig



Structure used to preinitialize Python:



  • Set the Python memory allocator


  • Configure the LC_CTYPE locale


  • Set the UTF-8 mode



Function to initialize a preconfiguration:




void
PyPreConfig_InitIsolatedConfig
(
PyPreConfig
 *preconfig
)



Initialize the preconfiguration with Python Configuration.






void
PyPreConfig_InitPythonConfig
(
PyPreConfig
 *preconfig
)



Initialize the preconfiguration with Isolated Configuration.




Structure fields:




int
allocator



Name of the memory allocator:



  • 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): force usage of malloc()


  • PYMEM_ALLOCATOR_MALLOC_DEBUG (4): force usage of malloc() 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_PYMALLOC and PYMEM_ALLOCATOR_PYMALLOC_DEBUG are not supported if Python is configured using --without-pymalloc


See Memory Management.






int
configure_locale



Set the LC_CTYPE locale to the user preferred locale? If equals to 0, set coerce_c_locale and coerce_c_locale_warn to 0.






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.






int
coerce_c_locale_warn



If non-zero, emit a warning if the C locale is coerced.






int
dev_mode



See PyConfig.dev_mode.






int
isolated



See PyConfig.isolated.






int
legacy_windows_fs_encoding
(Windows
 only
)



If non-zero, disable UTF-8 Mode, set the Python filesystem encoding to mbcs, set the filesystem error handler to replace.


Only available on Windows. #ifdef MS_WINDOWS macro can be used for Windows specific code.






int
parse_argv



If non-zero, Py_PreInitializeFromArgs() and Py_PreInitializeFromBytesArgs() parse their argv argument the same way the regular Python parses command line arguments: see Command Line Arguments.






int
use_environment



See PyConfig.use_environment.






int
utf8_mode



If non-zero, enable the UTF-8 mode.








Preinitialization with PyPreConfig


Functions to preinitialize Python:




PyStatus
Py_PreInitialize
(const
PyPreConfig
 *preconfig
)



Preinitialize Python from preconfig preconfiguration.






PyStatus
Py_PreInitializeFromBytesArgs
(const
PyPreConfig
 *preconfig, int
 argc, char * const
 *argv
)



Preinitialize Python from preconfig preconfiguration and command line arguments (bytes strings).






PyStatus
Py_PreInitializeFromArgs
(const
PyPreConfig
 *preconfig, int
 argc, wchar_t * const *
 argv
)



Preinitialize Python from preconfig preconfiguration and command line arguments (wide strings).




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 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 Python preinitialization, whereas calling directly malloc() and free() is always safe. Py_DecodeLocale() must not be called before the preinitialization.


Example using the preinitialization to enable the 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 will speak UTF-8 */

Py_Initialize();
/* ... use Python API here ... */
Py_Finalize();





PyConfig




PyConfig



Structure containing most parameters to configure Python.


Structure methods:




void
PyConfig_InitPythonConfig
(
PyConfig
 *config
)



Initialize configuration with Python Configuration.






void
PyConfig_InitIsolatedConfig
(
PyConfig
 *config
)



Initialize configuration with 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 from wide character strings.


Preinitialize Python if needed.






PyStatus
PyConfig_SetBytesArgv
(
PyConfig
 *config, int
 argc, char * const
 *argv
)



Set command line arguments: decode bytes using Py_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.


Preinitialize Python if needed.






void
PyConfig_Clear
(
PyConfig
 *config
)



Release configuration memory.




Most PyConfig methods preinitialize Python if needed. In that case, the Python preinitialization configuration in based on the PyConfig. If configuration fields which are in common with PyPreConfig are tuned, they must be set before calling a PyConfig method:



Moreover, if PyConfig_SetArgv() or PyConfig_SetBytesArgv() is used, this method must be called first, before other methods, since the preinitialization configuration depends on command line arguments (if parse_argv is non-zero).


The caller of these methods is responsible to handle exceptions (error or exit) using PyStatus_Exception() and Py_ExitStatusException().


Structure fields:




PyWideStringList
argv



Command line arguments, sys.argv. See parse_argv to parse argv the same way the regular Python parses Python command line arguments. If argv is empty, an empty string is added to ensure that sys.argv always exists and is never empty.






wchar_t*
base_exec_prefix



sys.base_exec_prefix.






wchar_t*
base_executable



sys._base_executable: __PYVENV_LAUNCHER__ environment variable value, or copy of PyConfig.executable.






wchar_t*
base_prefix



sys.base_prefix.






int
buffered_stdio



If equals to 0, enable unbuffered mode, making the stdout and stderr streams unbuffered.


stdin is always opened in buffered mode.






int
bytes_warning



If equals to 1, issue a warning when comparing bytes or bytearray with str, or comparing bytes with int. If equal or greater to 2, raise a BytesWarning exception.






wchar_t*
check_hash_pycs_mode



Control the validation behavior of hash-based .pyc files (see PEP 552): --check-hash-based-pycs command line option value.


Valid values: always, never and default.


The default value is: default.





Was it clear so far?

int
configure_c_stdio



If non-zero, configure C standard streams (stdio, stdout, stdout). For example, set their mode to O_BINARY on Windows.






int
dev_mode



Development mode: see -X dev.






int
dump_refs



If non-zero, dump all objects which are still alive at exit.


Require a debug build of Python (Py_REF_DEBUG macro must be defined).






wchar_t*
exec_prefix



sys.exec_prefix.






wchar_t*
executable



sys.executable.






int
faulthandler



If non-zero, call faulthandler.enable() at startup.






wchar_t*
filesystem_encoding



Filesystem encoding, sys.getfilesystemencoding().






wchar_t*
filesystem_errors



Filesystem encoding errors, sys.getfilesystemencodeerrors().






unsigned long
hash_seed






int
use_hash_seed



Randomized hash function seed.


If use_hash_seed is zero, a seed is chosen randomly at Pythonstartup, and hash_seed is ignored.






wchar_t*
home



Python home directory.


Initialized from PYTHONHOME environment variable value by default.






int
import_time



If non-zero, profile import time.






int
inspect



Enter interactive mode after executing a script or a command.






int
install_signal_handlers



Install signal handlers?






int
interactive



Interactive mode.






int
isolated



If greater than 0, enable isolated mode:



  • sys.path contains neither the script's directory (computed from argv[0] or the current directory) nor the user's site-packages directory.


  • Python REPL doesn?t import readline nor enable default readline configuration on interactive prompts.


  • Set use_environment and user_site_directory to 0.







int
legacy_windows_stdio



If non-zero, use io.FileIO instead of io.WindowsConsoleIO for sys.stdin, sys.stdout and sys.stderr.


Only available on Windows. #ifdef MS_WINDOWS macro can be used for Windows specific code.






int
malloc_stats



If non-zero, dump statistics on Python pymalloc memory allocator at exit.


The option is ignored if Python is built using --without-pymalloc.






wchar_t*
pythonpath_env



Module search paths as a string separated by DELIM (os.path.pathsep).


Initialized from PYTHONPATH environment variable value by default.






PyWideStringList
module_search_paths






int
module_search_paths_set



sys.path. If module_search_paths_set is equal to 0, the module_search_paths is overridden by the function calculating the Path Configuration.






int
optimization_level



Compilation optimization level:



  • 0: Peephole optimizer (and __debug__ is set to True)


  • 1: Remove assertions, set __debug__ to False


  • 2: Strip docstrings







int
parse_argv



If non-zero, parse argv the same way the regular Python command line arguments, and strip Python arguments from argv: see Command Line Arguments.






int
parser_debug



If non-zero, turn on parser debugging output (for expert only, depending on compilation options).






int
pathconfig_warnings



If equal to 0, suppress warnings when calculating the Path Configuration (Unix only, Windows does not log any warning). Otherwise, warnings are written into stderr.






wchar_t*
prefix



sys.prefix.






wchar_t*
program_name



Program name. Used to initialize executable, and in early error messages.






wchar_t*
pycache_prefix



sys.pycache_prefix: .pyc cache prefix.


If NULL, sys.pycache_prefix is set to None.






int
quiet



Quiet mode. For example, don?t display the copyright and version messages in interactive mode.






wchar_t*
run_command



python3 -c COMMAND argument. Used by Py_RunMain().






wchar_t*
run_filename



python3 FILENAME argument. Used by Py_RunMain().






wchar_t*
run_module



python3 -m MODULE argument. Used by Py_RunMain().






int
show_alloc_count



Show allocation counts at exit?


Set to 1 by -X showalloccount command line option.


Need a special Python build with COUNT_ALLOCS macro defined.






int
show_ref_count



Show total reference count at exit?


Set to 1 by -X showrefcount command line option.


Need a debug build of Python (Py_REF_DEBUG macro must be defined).






int
site_import



Import the site module at startup?






int
skip_source_first_line



Skip the first line of the source?






wchar_t*
stdio_encoding






wchar_t*
stdio_errors



Encoding and encoding errors of sys.stdin, sys.stdout and sys.stderr.






int
tracemalloc



If non-zero, call tracemalloc.start() at startup.






int
use_environment



If greater than 0, use environment variables.






int
user_site_directory



If non-zero, add user site directory to sys.path.






int
verbose



If non-zero, enable verbose mode.






PyWideStringList
warnoptions



sys.warnoptions: options of the warnings module to build warnings filters: lowest to highest priority.


The warnings module adds sys.warnoptions in the reverse order: the last PyConfig.warnoptions item becomes the first item of warnings.filters which is checked first (highest priority).






int
write_bytecode



If non-zero, write .pyc files.


sys.dont_write_bytecode is initialized to the inverted value of write_bytecode.






PyWideStringList
xoptions



sys._xoptions.






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: see Command Line Arguments.


The xoptions options are parsed to set other options: see -X option.




Initialization with PyConfig


Function to initialize Python:




PyStatus
Py_InitializeFromConfig
(const
PyConfig
 *config
)



Initialize Python from config configuration.




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.


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 fail;
}

status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto fail;
}
PyConfig_Clear(&config);
return;

fail:
PyConfig_Clear(&config);
Py_ExitStatusException(status);
}



More complete example modifying the default configuration, read the configuration, and then override some parameters:




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;
}

/* Append our custom search path to sys.path */
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, environments 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. Set the Path Configuration (?output fields?) to ignore these configuration files and avoid the function 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 UTF-8 Mode (PEP 540) depending on the LC_CTYPE locale, PYTHONUTF8 and PYTHONCOERCECLOCALE environment variables.


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 fail;
}

status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto fail;
}
PyConfig_Clear(&config);

return Py_RunMain();

fail:
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);
}






Path Configuration


PyConfig contains multiple fields for the path configuration:



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, path configuration input fields are ignored as well.


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 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:



The __PYVENV_LAUNCHER__ environment variable is used to set PyConfig.base_executable




Py_RunMain()




int
Py_RunMain
(void
)



Execute the command (PyConfig.run_command), the script (PyConfig.run_filename) or the module (PyConfig.run_module) specified on the command line or in the configuration.


By default and when if -i option is used, run the REPL.


Finally, finalizes Python and returns an exit status that can be passed to the exit() function.




See Python Configuration for an example of customized Python always running in isolated mode using Py_RunMain().




Multi-Phase Initialization Private Provisional API


This section is a private provisional API introducing multi-phase initialization, the core feature of the PEP 432:



Private provisional API:





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 calculatin 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);
}
}








Topic Graph | Check Your Progress | Propose QnA | Have a question or comments for open discussion?
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




PyPreConfig



Structure used to preinitialize Python:



  • Set the Python memory allocator


  • Configure the LC_CTYPE locale


  • Set the UTF-8 mode



Function to initialize a preconfiguration:




void
PyPreConfig_InitIsolatedConfig
(
PyPreConfig
 *preconfig
)



Initialize the preconfiguration with Python Configuration.






void
PyPreConfig_InitPythonConfig
(
PyPreConfig
 *preconfig
)



Initialize the preconfiguration with Isolated Configuration.




Structure fields:




int
allocator



Name of the memory allocator:



  • 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): force usage of malloc()


  • PYMEM_ALLOCATOR_MALLOC_DEBUG (4): force usage of malloc() 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_PYMALLOC and PYMEM_ALLOCATOR_PYMALLOC_DEBUG are not supported if Python is configured using --without-pymalloc


See Memory Management.






int
configure_locale



Set the LC_CTYPE locale to the user preferred locale? If equals to 0, set coerce_c_locale and coerce_c_locale_warn to 0.






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.






int
coerce_c_locale_warn



If non-zero, emit a warning if the C locale is coerced.






int
dev_mode



See PyConfig.dev_mode.






int
isolated



See PyConfig.isolated.






int
legacy_windows_fs_encoding
(Windows
 only
)



If non-zero, disable UTF-8 Mode, set the Python filesystem encoding to mbcs, set the filesystem error handler to replace.


Only available on Windows. #ifdef MS_WINDOWS macro can be used for Windows specific code.






int
parse_argv



If non-zero, Py_PreInitializeFromArgs() and Py_PreInitializeFromBytesArgs() parse their argv argument the same way the regular Python parses command line arguments: see Command Line Arguments.






int
use_environment



See PyConfig.use_environment.






int
utf8_mode



If non-zero, enable the UTF-8 mode.








Preinitialization with PyPreConfig


Functions to preinitialize Python:




PyStatus
Py_PreInitialize
(const
PyPreConfig
 *preconfig
)



Preinitialize Python from preconfig preconfiguration.






PyStatus
Py_PreInitializeFromBytesArgs
(const
PyPreConfig
 *preconfig, int
 argc, char * const
 *argv
)



Preinitialize Python from preconfig preconfiguration and command line arguments (bytes strings).






PyStatus
Py_PreInitializeFromArgs
(const
PyPreConfig
 *preconfig, int
 argc, wchar_t * const *
 argv
)



Preinitialize Python from preconfig preconfiguration and command line arguments (wide strings).




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 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 Python preinitialization, whereas calling directly malloc() and free() is always safe. Py_DecodeLocale() must not be called before the preinitialization.


Example using the preinitialization to enable the 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 will speak UTF-8 */

Py_Initialize();
/* ... use Python API here ... */
Py_Finalize();





PyConfig




PyConfig



Structure containing most parameters to configure Python.


Structure methods:




void
PyConfig_InitPythonConfig
(
PyConfig
 *config
)



Initialize configuration with Python Configuration.






void
PyConfig_InitIsolatedConfig
(
PyConfig
 *config
)



Initialize configuration with 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 from wide character strings.


Preinitialize Python if needed.






PyStatus
PyConfig_SetBytesArgv
(
PyConfig
 *config, int
 argc, char * const
 *argv
)



Set command line arguments: decode bytes using Py_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.


Preinitialize Python if needed.






void
PyConfig_Clear
(
PyConfig
 *config
)



Release configuration memory.




Most PyConfig methods preinitialize Python if needed. In that case, the Python preinitialization configuration in based on the PyConfig. If configuration fields which are in common with PyPreConfig are tuned, they must be set before calling a PyConfig method:



Moreover, if PyConfig_SetArgv() or PyConfig_SetBytesArgv() is used, this method must be called first, before other methods, since the preinitialization configuration depends on command line arguments (if parse_argv is non-zero).


The caller of these methods is responsible to handle exceptions (error or exit) using PyStatus_Exception() and Py_ExitStatusException().


Structure fields:




PyWideStringList
argv



Command line arguments, sys.argv. See parse_argv to parse argv the same way the regular Python parses Python command line arguments. If argv is empty, an empty string is added to ensure that sys.argv always exists and is never empty.






wchar_t*
base_exec_prefix



sys.base_exec_prefix.






wchar_t*
base_executable



sys._base_executable: __PYVENV_LAUNCHER__ environment variable value, or copy of PyConfig.executable.






wchar_t*
base_prefix



sys.base_prefix.






int
buffered_stdio



If equals to 0, enable unbuffered mode, making the stdout and stderr streams unbuffered.


stdin is always opened in buffered mode.






int
bytes_warning



If equals to 1, issue a warning when comparing bytes or bytearray with str, or comparing bytes with int. If equal or greater to 2, raise a BytesWarning exception.






wchar_t*
check_hash_pycs_mode



Control the validation behavior of hash-based .pyc files (see PEP 552): --check-hash-based-pycs command line option value.


Valid values: always, never and default.


The default value is: default.











Was it clear so far?


int
configure_c_stdio



If non-zero, configure C standard streams (stdio, stdout, stdout). For example, set their mode to O_BINARY on Windows.






int
dev_mode



Development mode: see -X dev.






int
dump_refs



If non-zero, dump all objects which are still alive at exit.


Require a debug build of Python (Py_REF_DEBUG macro must be defined).






wchar_t*
exec_prefix



sys.exec_prefix.






wchar_t*
executable



sys.executable.






int
faulthandler



If non-zero, call faulthandler.enable() at startup.






wchar_t*
filesystem_encoding



Filesystem encoding, sys.getfilesystemencoding().






wchar_t*
filesystem_errors



Filesystem encoding errors, sys.getfilesystemencodeerrors().






unsigned long
hash_seed






int
use_hash_seed



Randomized hash function seed.


If use_hash_seed is zero, a seed is chosen randomly at Pythonstartup, and hash_seed is ignored.






wchar_t*
home



Python home directory.


Initialized from PYTHONHOME environment variable value by default.






int
import_time



If non-zero, profile import time.






int
inspect



Enter interactive mode after executing a script or a command.






int
install_signal_handlers



Install signal handlers?






int
interactive



Interactive mode.






int
isolated



If greater than 0, enable isolated mode:



  • sys.path contains neither the script's directory (computed from argv[0] or the current directory) nor the user's site-packages directory.


  • Python REPL doesn?t import readline nor enable default readline configuration on interactive prompts.


  • Set use_environment and user_site_directory to 0.







int
legacy_windows_stdio



If non-zero, use io.FileIO instead of io.WindowsConsoleIO for sys.stdin, sys.stdout and sys.stderr.


Only available on Windows. #ifdef MS_WINDOWS macro can be used for Windows specific code.






int
malloc_stats



If non-zero, dump statistics on Python pymalloc memory allocator at exit.


The option is ignored if Python is built using --without-pymalloc.






wchar_t*
pythonpath_env



Module search paths as a string separated by DELIM (os.path.pathsep).


Initialized from PYTHONPATH environment variable value by default.






PyWideStringList
module_search_paths






int
module_search_paths_set



sys.path. If module_search_paths_set is equal to 0, the module_search_paths is overridden by the function calculating the Path Configuration.






int
optimization_level



Compilation optimization level:



  • 0: Peephole optimizer (and __debug__ is set to True)


  • 1: Remove assertions, set __debug__ to False


  • 2: Strip docstrings







int
parse_argv



If non-zero, parse argv the same way the regular Python command line arguments, and strip Python arguments from argv: see Command Line Arguments.






int
parser_debug



If non-zero, turn on parser debugging output (for expert only, depending on compilation options).






int
pathconfig_warnings



If equal to 0, suppress warnings when calculating the Path Configuration (Unix only, Windows does not log any warning). Otherwise, warnings are written into stderr.






wchar_t*
prefix



sys.prefix.






wchar_t*
program_name



Program name. Used to initialize executable, and in early error messages.






wchar_t*
pycache_prefix



sys.pycache_prefix: .pyc cache prefix.


If NULL, sys.pycache_prefix is set to None.






int
quiet



Quiet mode. For example, don?t display the copyright and version messages in interactive mode.






wchar_t*
run_command



python3 -c COMMAND argument. Used by Py_RunMain().






wchar_t*
run_filename



python3 FILENAME argument. Used by Py_RunMain().






wchar_t*
run_module



python3 -m MODULE argument. Used by Py_RunMain().






int
show_alloc_count



Show allocation counts at exit?


Set to 1 by -X showalloccount command line option.


Need a special Python build with COUNT_ALLOCS macro defined.






int
show_ref_count



Show total reference count at exit?


Set to 1 by -X showrefcount command line option.


Need a debug build of Python (Py_REF_DEBUG macro must be defined).






int
site_import



Import the site module at startup?






int
skip_source_first_line



Skip the first line of the source?






wchar_t*
stdio_encoding






wchar_t*
stdio_errors



Encoding and encoding errors of sys.stdin, sys.stdout and sys.stderr.






int
tracemalloc



If non-zero, call tracemalloc.start() at startup.






int
use_environment



If greater than 0, use environment variables.






int
user_site_directory



If non-zero, add user site directory to sys.path.






int
verbose



If non-zero, enable verbose mode.






PyWideStringList
warnoptions



sys.warnoptions: options of the warnings module to build warnings filters: lowest to highest priority.


The warnings module adds sys.warnoptions in the reverse order: the last PyConfig.warnoptions item becomes the first item of warnings.filters which is checked first (highest priority).






int
write_bytecode



If non-zero, write .pyc files.


sys.dont_write_bytecode is initialized to the inverted value of write_bytecode.






PyWideStringList
xoptions



sys._xoptions.






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: see Command Line Arguments.


The xoptions options are parsed to set other options: see -X option.




Initialization with PyConfig


Function to initialize Python:




PyStatus
Py_InitializeFromConfig
(const
PyConfig
 *config
)



Initialize Python from config configuration.




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.


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 fail;
}

status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto fail;
}
PyConfig_Clear(&config);
return;

fail:
PyConfig_Clear(&config);
Py_ExitStatusException(status);
}



More complete example modifying the default configuration, read the configuration, and then override some parameters:




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;
}

/* Append our custom search path to sys.path */
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, environments 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. Set the Path Configuration (?output fields?) to ignore these configuration files and avoid the function 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 UTF-8 Mode (PEP 540) depending on the LC_CTYPE locale, PYTHONUTF8 and PYTHONCOERCECLOCALE environment variables.


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 fail;
}

status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto fail;
}
PyConfig_Clear(&config);

return Py_RunMain();

fail:
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);
}






Path Configuration


PyConfig contains multiple fields for the path configuration:



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, path configuration input fields are ignored as well.


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 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:



The __PYVENV_LAUNCHER__ environment variable is used to set PyConfig.base_executable




Py_RunMain()




int
Py_RunMain
(void
)



Execute the command (PyConfig.run_command), the script (PyConfig.run_filename) or the module (PyConfig.run_module) specified on the command line or in the configuration.


By default and when if -i option is used, run the REPL.


Finally, finalizes Python and returns an exit status that can be passed to the exit() function.




See Python Configuration for an example of customized Python always running in isolated mode using Py_RunMain().




Multi-Phase Initialization Private Provisional API


This section is a private provisional API introducing multi-phase initialization, the core feature of the PEP 432:



Private provisional API:





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 calculatin 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);
}
}









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