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, environment variables and command line arguments are used to configure Python.
The Isolated Configuration can be used to embed Python into an application. It isolates Python from the system. For example, environment variables are ignored, the LC_CTYPE locale is left unchanged and no signal handler is registered.
The Py_RunMain()
function can be used to write a customized Python
program.
See also Initialization, Finalization, and Threads.
See also
PEP 587 “Python Initialization Configuration”.
Example¶
Example of customized Python always running in isolated mode:
int main(int argc, char **argv)
{
PyStatus status;
PyConfig config;
PyConfig_InitPythonConfig(&config);
config.isolated = 1;
/* Decode command line arguments.
Implicitly preinitialize Python (in isolated mode). */
status = PyConfig_SetBytesArgv(&config, argc, argv);
if (PyStatus_Exception(status)) {
goto exception;
}
status = Py_InitializeFromConfig(&config);
if (PyStatus_Exception(status)) {
goto exception;
}
PyConfig_Clear(&config);
return Py_RunMain();
exception:
PyConfig_Clear(&config);
if (PyStatus_IsExit(status)) {
return status.exitcode;
}
/* Display the error message and exit the process with
non-zero exit code */
Py_ExitStatusException(status);
}
PyWideStringList¶
-
type
PyWideStringList
¶ List of
wchar_t*
strings.If length is non-zero, items must be non-
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¶
-
type
PyStatus
¶ Structure to store an initialization function status: success, error or exit.
For an error, it can store the C function name which created the error.
Structure fields:
-
int
exitcode
¶ Exit code. Argument passed to
exit()
.
-
const char *
err_msg
¶ Error message.
-
const char *
func
¶ Name of the function which created an error, can be
NULL
.
Functions to create a status:
-
PyStatus
PyStatus_Error
(const char *err_msg)¶ Initialization error with a message.
err_msg must not be
NULL
.
Functions to handle a status:
-
int
PyStatus_Exception
(PyStatus status)¶ Is the status an error or an exit? If true, the exception must be handled; by calling
Py_ExitStatusException()
for example.
-
int
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 isconfigured 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
andcoerce_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
to0
,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()
andPy_PreInitializeFromBytesArgs()
parse theirargv
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 thePYTHONUTF8
environment variable.Default:
-1
in Python config and0
in isolated config.
-
void
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 usingPy_DecodeLocale()
.Preinitialize Python if needed.
-
PyStatus
PyConfig_SetWideStringList
(PyConfig *config, PyWideStringList *list, Py_ssize_t length, wchar_t **items)¶ Set the list of wide strings list to length and items.
Preinitialize Python if needed.
-
PyStatus
PyConfig_Read
(PyConfig *config)¶ Read all Python configuration.
Fields which are already initialized are left unchanged.
The
PyConfig_Read()
function only parsesPyConfig.argv
arguments once:PyConfig.parse_argv
is set to2
after arguments are parsed. Since Python arguments are strippped fromPyConfig.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 to2
after arguments are parsed, and arguments are only parsed ifPyConfig.parse_argv
equals1
.
Most
PyConfig
methods preinitialize Python if needed. In that case, the Python preinitialization configuration (PyPreConfig
) in based on thePyConfig
. If configuration fields which are in common withPyPreConfig
are tuned, they must be set before calling aPyConfig
method:Moreover, if
PyConfig_SetArgv()
orPyConfig_SetBytesArgv()
is used, this method must be called before other methods, since the preinitialization configuration depends on command line arguments (ifparse_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
to1
to parseargv
the same way the regular Python parses Python command line arguments and then to strip Python arguments fromargv
.If
argv
is empty, an empty string is added to ensure thatsys.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
ifNULL
.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 thePYTHONUNBUFFERED
environment variable.stdin is always opened in buffered mode.
Default:
1
.
-
int
bytes_warning
¶ If equals to 1, issue a warning when comparing
bytes
orbytearray
withstr
, or comparingbytes
withint
.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 whenio.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 references?
If non-zero, dump all objects which are still alive at exit.
Set to
1
by thePYTHONDUMPREFS
environment variable.Need a special build of Python with the
Py_TRACE_REFS
macro defined: see theconfigure --with-trace-refs option
.Default:
0
.
-
wchar_t *
exec_prefix
¶ The site-specific directory prefix where the platform-dependent Python files are installed:
sys.exec_prefix
.Default:
NULL
.Part of the Python Path Configuration output.
-
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 thePYTHONFAULTHANDLER
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"
iflegacy_windows_fs_encoding
ofPyPreConfig
is non-zero.Default encoding on other platforms:
"utf-8"
ifPyPreConfig.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"
iflegacy_windows_fs_encoding
ofPyPreConfig
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, andhash_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 notNULL
.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 thePYTHONPROFILEIMPORTTIME
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 to1
if thePYTHONINSPECT
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 fromargv[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
anduser_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 ofio.WindowsConsoleIO
forsys.stdin
,sys.stdout
andsys.stderr
.Set to
1
if thePYTHONLEGACYWINDOWSSTDIO
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 thePYTHONMALLOCSTATS
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 theconfigure --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 byDELIM
(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 themodule_search_paths
and setsmodule_search_paths_set
to1
.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 thePYTHONOPTIMIZE
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 andargv
is not a list only containing an empty string,PyConfig_Read()
copiesargv
intoorig_argv
before modifyingargv
(ifparse_argv
is non-zero).See also the
argv
member and thePy_GetArgcArgv()
function.Default: empty list.
New in version 3.10.
-
int
parse_argv
¶ Parse command line arguments?
If equals to
1
, parseargv
the same way the regular Python parses command line arguments, and strip Python arguments fromargv
.The
PyConfig_Read()
function only parsesPyConfig.argv
arguments once:PyConfig.parse_argv
is set to2
after arguments are parsed. Since Python arguments are strippped fromPyConfig.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 ifPyConfig.parse_argv
equals to1
.
-
int
parser_debug
¶ Parser debug mode. If greater than 0, turn on parser debugging output (for expert only, depending on compilation options).
Incremented by the
-d
command line option. Set to thePYTHONDEBUG
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]
ofargv
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 thePYTHONPYCACHEPREFIX
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 (callsite.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 ofsite_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
andsys.stderr
(butsys.stderr
always uses"backslashreplace"
error handler).If
Py_SetStandardStreamEncoding()
has been called, use its error and errors arguments if they are notNULL
.Use the
PYTHONIOENCODING
environment variable if it is non-empty.Default encoding:
"UTF-8"
ifPyPreConfig.utf8_mode
is non-zero.Otherwise, use the locale encoding.
Default error handler:
On Windows: use
"surrogateescape"
."surrogateescape"
ifPyPreConfig.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 thePYTHONTRACEMALLOC
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 thePYTHONNOUSERSITE
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 addssys.warnoptions
in the reverse order: the lastPyConfig.warnoptions
item becomes the first item ofwarnings.filters
which is checked first (highest priority).The
-W
command line options adds its value towarnoptions
, 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 thePYTHONDONTWRITEBYTECODE
environment variable.sys.dont_write_bytecode
is initialized to the inverted value ofwrite_bytecode
.Default:
1
.
-
PyWideStringList
xoptions
¶ Values of the
-X
command line options:sys._xoptions
.Default: empty list.
-
void
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:
-
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. 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, environment
variables, command line arguments (PyConfig.argv
is not parsed)
and user site directory. The C standard streams (ex: stdout
) and the
LC_CTYPE locale are left unchanged. Signal handlers are not installed.
Configuration files are still used with this configuration. 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:
current working directory: to get absolute paths
PATH
environment variable to get the program full path (fromPyConfig.program_name
)__PYVENV_LAUNCHER__
environment variable(Windows only) Application paths in the registry under “SoftwarePythonPythonCoreX.YPythonPath” of HKEY_CURRENT_USER and HKEY_LOCAL_MACHINE (where X.Y is the Python version).
Path configuration output fields:
If at least one “output field” is not set, Python calculates the path
configuration to fill unset fields. If
module_search_paths_set
is equal to 0,
module_search_paths
is overridden and
module_search_paths_set
is set to 1.
It is possible to completely ignore the function calculating the default
path configuration by setting explicitly all path configuration output
fields listed above. A string is considered as set even if it is non-empty.
module_search_paths
is considered as set if
module_search_paths_set
is set to 1. In this case, 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, prependrun_filename
tosys.path
.If
isolated
is zero:If
run_module
is set, prepend the current directory tosys.path
. Do nothing if the current directory cannot be read.If
run_filename
is set, prepend the directory of the filename tosys.path
.Otherwise, prepend an empty string to
sys.path
.
If site_import
is non-zero, sys.path
can be
modified by the site
module. If
user_site_directory
is non-zero and the user’s
site-package directory exists, the site
module appends the user’s
site-package directory to sys.path
.
The following configuration files are used by the path configuration:
pyvenv.cfg
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 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: createsys.stdout
andsys.path
);Enable optional features like
faulthandler
andtracemalloc
;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);
}
}