Python Initialization Configuration — Python documentation
Python Initialization Configuration
New 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, environments 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, environments 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.
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-
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.
err_msg must not be
NULL
.
- 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.
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_PYMALLOC
andPYMEM_ALLOCATOR_PYMALLOC_DEBUG
are not supported if Python is configured using --without-pymalloc.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, set coerce_c_locale and coerce_c_locale_warn members to 0.
See the locale encoding.
Default:
1
in Python config,0
in 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:
-1
in Python config,0
in isolated config.
- int coerce_c_locale_warn
If non-zero, emit a warning if the C locale is coerced.
Default:
-1
in Python config,0
in isolated config.
- int dev_mode
If non-zero, enables the Python Development Mode: see PyConfig.dev_mode.
Default:
-1
in Python mode,0
in isolated mode.
- int isolated
Isolated mode: see PyConfig.isolated.
Default:
0
in Python mode,1
in isolated mode.
- int legacy_windows_fs_encoding
If non-zero:
Set PyPreConfig.utf8_mode to
0
,Set PyConfig.filesystem_encoding to
"mbcs"
,Set PyConfig.filesystem_errors to
"replace"
.
Initialized the from PYTHONLEGACYWINDOWSFSENCODING environment variable value.
Only available on Windows.
#ifdef MS_WINDOWS
macro can be used for Windows specific code.Default:
0
.
- 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.Default:
1
in Python config,0
in isolated config.
- int use_environment
Use environment variables? See PyConfig.use_environment.
Default:
1
in Python config and0
in isolated config.
- int utf8_mode
If non-zero, enable the Python UTF-8 Mode.
Set by the -X utf8 command line option and the PYTHONUTF8 environment variable.
Default:
-1
in Python config and0
in 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_argv of 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_argv of 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 (argv member 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 (argv member of config) from the argv list of bytes strings. 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.
The PyConfig_Read() function only parses PyConfig.argv arguments once: PyConfig.parse_argv is set to
2
after arguments are parsed. Since Python arguments are strippped from PyConfig.argv, parsing arguments twice would parse the application options as Python options.Preinitialize Python if needed.
Changed in version 3.10: The PyConfig.argv arguments are now only parsed once, PyConfig.parse_argv is set to
2
after arguments are parsed, and arguments are only parsed if PyConfig.parse_argv equals1
.
- void PyConfig_Clear(PyConfig *config)
Release configuration memory.
Most
PyConfig
methods preinitialize Python if needed. In that case, the Python preinitialization configuration (PyPreConfig) 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 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.
Set parse_argv to
1
to parse argv the same way the regular Python parses Python command line arguments and then to strip Python arguments from argv.If argv is empty, an empty string is added to ensure that sys.argv always exists and is never empty.
Default:
NULL
.See also the orig_argv member.
- wchar_t *base_exec_prefix
-
Default:
NULL
.Part of the Python Path Configuration output.
- wchar_t *base_executable
Python base executable:
sys._base_executable
.Set by the
__PYVENV_LAUNCHER__
environment variable.Set from PyConfig.executable if
NULL
.Default:
NULL
.Part of the Python Path Configuration output.
- wchar_t *base_prefix
-
Default:
NULL
.Part of the Python Path Configuration output.
- int buffered_stdio
If equals to 0 and configure_c_stdio is non-zero, disable buffering on the C streams stdout and stderr.
Set to 0 by the -u command line option and the PYTHONUNBUFFERED environment variable.
stdin is always opened in buffered mode.
Default:
1
.
- 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 in these cases.
Incremented by the -b command line option.
Default:
0
.
- int warn_default_encoding
If non-zero, emit a EncodingWarning warning when io.TextIOWrapper uses its default encoding. See Opt-in EncodingWarning for details.
Default:
0
.New in version 3.10.
- wchar_t *check_hash_pycs_mode
Control the validation behavior of hash-based
.pyc
files: value of the --check-hash-based-pycs command 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_stdio equals zero, disable buffering of stdin, stdout and stderr streams.
If interactive is non-zero, enable stream buffering on stdin and stdout (only stdout on Windows).
Default:
1
in Python config,0
in isolated config.
- int dev_mode
If non-zero, enable the Python Development Mode.
Default:
-1
in Python mode,0
in isolated mode.
- int dump_refs
Dump Python refererences?
If non-zero, dump all objects which are still alive at exit.
Set to
1
by the PYTHONDUMPREFS environment variable.Need a special build of Python with the
Py_TRACE_REFS
macro defined: see the configure --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.
- 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.
- int faulthandler
Enable faulthandler?
If non-zero, call faulthandler.enable() at startup.
Set to
1
by -X faulthandler and the PYTHONFAULTHANDLER environment variable.Default:
-1
in Python mode,0
in 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"
if legacy_windows_fs_encoding of PyPreConfig is non-zero.Default encoding on other platforms:
"utf-8"
if PyPreConfig.utf8_mode is non-zero."ascii"
if Python detects thatnl_langinfo(CODESET)
announces the ASCII encoding (or Roman8 encoding on HP-UX), 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_errors member.
- wchar_t *filesystem_errors
Filesystem error handler: sys.getfilesystemencodeerrors().
On Windows: use
"surrogatepass"
by default, or"replace"
if legacy_windows_fs_encoding of PyPreConfig is 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_encoding member.
- unsigned long hash_seed
- int use_hash_seed
Randomized hash function seed.
If use_hash_seed is zero, a seed is chosen randomly at Python startup, and hash_seed is ignored.
Set by the PYTHONHASHSEED environment variable.
Default use_hash_seed value:
-1
in Python mode,0
in isolated mode.
- wchar_t *home
Python home directory.
If Py_SetPythonHome() has been called, use its argument if it is not
NULL
.Set by the PYTHONHOME environment variable.
Default:
NULL
.Part of the Python Path Configuration input.
- int import_time
If non-zero, profile import time.
Set the
1
by the -X importtime option and the PYTHONPROFILEIMPORTTIME environment 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 when sys.stdin does not appear to be a terminal.
Incremented by the -i command line option. Set to
1
if the PYTHONINSPECT environment variable is non-empty.Default:
0
.
- int install_signal_handlers
Install Python signal handlers?
Default:
1
in Python mode,0
in isolated mode.
- int interactive
If greater than 0, enable the interactive mode (REPL).
Incremented by the -i command line option.
Default:
0
.
- 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.
Default:
0
in Python mode,1
in isolated mode.See also PyPreConfig.isolated.
- int legacy_windows_stdio
If non-zero, use io.FileIO instead of
io.WindowsConsoleIO
for sys.stdin, sys.stdout and sys.stderr.Set to
1
if the PYTHONLEGACYWINDOWSSTDIO environment variable is set to a non-empty string.Only available on Windows.
#ifdef MS_WINDOWS
macro 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
1
by the PYTHONMALLOCSTATS environment 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 PYTHONPLATLIBDIR environment variable.
Default: value of the
PLATLIBDIR
macro which is set by the configure --with-platlibdir option (default:"lib"
).Part of the Python Path Configuration input.
New in version 3.9.
- wchar_t *pythonpath_env
Module search paths (sys.path) as a string separated by
DELIM
(os.path.pathsep
).Set by the PYTHONPATH environment 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_set is equal to 0, the function calculating the Python Path Configuration overrides the module_search_paths and sets module_search_paths_set to
1
.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 -O command line option. Set to the PYTHONOPTIMIZE environment 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_argv list is empty and argv is not a list only containing an empty string, PyConfig_Read() copies argv into orig_argv before modifying argv (if parse_argv is non-zero).
See also the argv member and the Py_GetArgcArgv() function.
Default: empty list.
New in version 3.10.
- int parse_argv
Parse command line arguments?
If equals to
1
, parse argv the same way the regular Python parses command line arguments, and strip Python arguments from argv.The PyConfig_Read() function only parses PyConfig.argv arguments once: PyConfig.parse_argv is set to
2
after arguments are parsed. Since Python arguments are strippped from PyConfig.argv, parsing arguments twice would parse the application options as Python options.Default:
1
in Python mode,0
in isolated mode.Changed in version 3.10: The PyConfig.argv arguments are now only parsed if PyConfig.parse_argv equals to
1
.
- 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 -d command line option. Set to the PYTHONDEBUG environment variable value.
Default:
0
.
- int pathconfig_warnings
On Unix, if non-zero, calculating the Python Path Configuration can log warnings into
stderr
. If equals to 0, suppress these warnings.It has no effect on Windows.
Default:
1
in Python mode,0
in isolated mode.Part of the Python Path Configuration input.
- 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.
- wchar_t *program_name
Program name used to initialize executable and in early error messages during Python initialization.
If
Py_SetProgramName()
has been called, use its argument.On macOS, use PYTHONEXECUTABLE environment variable if set.
If the
WITH_NEXT_FRAMEWORK
macro is defined, use__PYVENV_LAUNCHER__
environment variable if set.Use
argv[0]
of argv if 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
.pyc
files are written: sys.pycache_prefix.Set by the -X pycache_prefix=PATH command line option and the PYTHONPYCACHEPREFIX environment variable.
If
NULL
, sys.pycache_prefix is 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 -q command line option.
Default:
0
.
- wchar_t *run_command
Value of the -c command line option.
Used by Py_RunMain().
Default:
NULL
.
- wchar_t *run_filename
Filename passed on the command line: trailing command line argument without -c or -m.
For example, it is set to
script.py
by thepython3 script.py arg
command.Used by Py_RunMain().
Default:
NULL
.
- wchar_t *run_module
Value of the -m command line option.
Used by Py_RunMain().
Default:
NULL
.
- 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 (the
Py_REF_DEBUG
macro must be defined).Default:
0
.
- int site_import
Import the site module at startup?
If equal to zero, disable the import of the module site and the site-dependent manipulations of sys.path that it entails.
Also disable these manipulations if the site module is explicitly imported later (call site.main() if you want them to be triggered).
Set to
0
by the -S command line option.sys.flags.no_site
is set to the inverted value of site_import.Default:
1
.
- int skip_source_first_line
If non-zero, skip the first line of the PyConfig.run_filename source.
It allows the usage of non-Unix forms of
#!cmd
. This is intended for a DOS specific hack only.Set to
1
by the -x command line option.Default:
0
.
- wchar_t *stdio_encoding
- wchar_t *stdio_errors
Encoding and encoding errors of sys.stdin, sys.stdout and sys.stderr (but sys.stderr always uses
"backslashreplace"
error handler).If Py_SetStandardStreamEncoding() has been called, use its error and errors arguments if they are not
NULL
.Use the PYTHONIOENCODING environment variable if it is non-empty.
Default encoding:
"UTF-8"
if PyPreConfig.utf8_mode is non-zero.Otherwise, use the locale encoding.
Default error handler:
On Windows: use
"surrogateescape"
."surrogateescape"
if PyPreConfig.utf8_mode is non-zero, or if the LC_CTYPE locale is “C” or “POSIX”."strict"
otherwise.
- int tracemalloc
Enable tracemalloc?
If non-zero, call tracemalloc.start() at startup.
Set by -X tracemalloc=N command line option and by the PYTHONTRACEMALLOC environment variable.
Default:
-1
in Python mode,0
in isolated mode.
- int use_environment
-
If equals to zero, ignore the environment variables.
Default:
1
in Python config and0
in isolated config.
- int user_site_directory
If non-zero, add the user site directory to sys.path.
Set to
0
by the -s and -I command line options.Set to
0
by the PYTHONNOUSERSITE environment variable.Default:
1
in Python mode,0
in 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 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 -v command line option.
Set to the PYTHONVERBOSE environment variable value.
Default:
0
.
- PyWideStringList warnoptions
Options of the warnings module to build warnings filters, lowest to highest priority: sys.warnoptions.
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).The -W command line options adds its value to warnoptions, it can be used multiple times.
The PYTHONWARNINGS environment 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
.pyc
files on the import of source modules.Set to
0
by the -B command line option and the PYTHONDONTWRITEBYTECODE environment variable.sys.dont_write_bytecode is initialized to the inverted value of write_bytecode.
Default:
1
.
- PyWideStringList xoptions
Values of the -X command 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
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. 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:
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 Python 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 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:
PyConfig.home
PyConfig.platlibdir
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().
Py_GetArgcArgv()
- void Py_GetArgcArgv(int *argc, wchar_t ***argv)
Get the original command line arguments, before Python modified them.
See also PyConfig.orig_argv member.
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.PyConfig._isolated_interpreter
: if non-zero, disallow threads, subprocesses and fork.
- 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);
}
}