Python Initialization Configuration — Python documentation
Python Initialization Configuration
New in version 3.8.
Structures:
Functions:
PyConfig_Clear()
PyConfig_InitIsolatedConfig()
PyConfig_InitPythonConfig()
PyConfig_Read()
PyConfig_SetArgv()
PyConfig_SetBytesArgv()
PyConfig_SetBytesString()
PyConfig_SetString()
PyConfig_SetWideStringList()
PyPreConfig_InitIsolatedConfig()
PyPreConfig_InitPythonConfig()
PyStatus_Error()
PyStatus_Exception()
PyStatus_Exit()
PyStatus_IsError()
PyStatus_IsExit()
PyStatus_NoMemory()
PyStatus_Ok()
PyWideStringList_Append()
PyWideStringList_Insert()
Py_ExitStatusException()
Py_InitializeFromConfig()
Py_PreInitialize()
Py_PreInitializeFromArgs()
Py_PreInitializeFromBytesArgs()
Py_RunMain()
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.
PyWideStringList
- type 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 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_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 ifPyStatus_Exception(status)
is non-zero.
- 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:
Set the Python memory allocator
Configure the LC_CTYPE locale
Set the UTF-8 mode
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 memory allocator:
PYMEM_ALLOCATOR_NOT_SET
(0
): don’t change memory allocators (use defaults)PYMEM_ALLOCATOR_DEFAULT
(1
): default memory allocatorsPYMEM_ALLOCATOR_DEBUG
(2
): default memory allocators with debug hooksPYMEM_ALLOCATOR_MALLOC
(3
): force usage ofmalloc()
PYMEM_ALLOCATOR_MALLOC_DEBUG
(4
): force usage ofmalloc()
with debug hooksPYMEM_ALLOCATOR_PYMALLOC
(5
): Python pymalloc memory allocatorPYMEM_ALLOCATOR_PYMALLOC_DEBUG
(6
): Python pymalloc memory allocator with debug hooks
PYMEM_ALLOCATOR_PYMALLOC
andPYMEM_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 toreplace
.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
- 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
- type 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()
andPy_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
- wchar_t *base_executable
sys._base_executable
:__PYVENV_LAUNCHER__
environment variable value, or copy of PyConfig.executable.
- wchar_t *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
anddefault
.The default value is:
default
.
- int configure_c_stdio
If non-zero, configure C standard streams (
stdio
,stdout
,stdout
). For example, set their mode toO_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
- wchar_t *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 toTrue
)1: Remove assertions, set
__debug__
toFalse
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
- 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 toNone
.
- 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
- 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
: see Command Line Arguments.
The xoptions
options are parsed to set other options: see -X option.
Initialization with PyConfig
Function to initialize Python:
- 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:
- Path configuration inputs:
PyConfig.home
PyConfig.pathconfig_warnings
PyConfig.program_name
PyConfig.pythonpath_env
- current working directory: to get absolute paths
PATH
environment variable to get the program full path (from PyConfig.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, 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 run_filename is set and is a directory which contains a
__main__.py
script, prepend run_filename to sys.path. - If isolated is zero:
- If run_module is set, prepend the current directory to sys.path. Do nothing if the current directory cannot be read.
- If run_filename is set, prepend the directory of the filename to sys.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
python._pth
(Windows only)pybuilddir.txt
(Unix only)
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:
- “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 sys module initialization (ex: create sys.stdout and sys.path);
- Enable optional features like faulthandler and tracemalloc;
- Import the site module;
- etc.
Private provisional API:
PyConfig._init_main
: if set to 0, 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 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);
}
}