sys --- 系統特定的參數與函式

---

This module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter. It is always available. Unless explicitly noted otherwise, all variables are read-only.

sys.abiflags

On POSIX systems where Python was built with the standard configure script, this contains the ABI flags as specified by PEP 3149.

在 3.2 版被加入.

在 3.8 版的變更: Default flags became an empty string (m flag for pymalloc has been removed).

可用性: Unix.

sys.addaudithook(hook)

Append the callable hook to the list of active auditing hooks for the current (sub)interpreter.

When an auditing event is raised through the sys.audit() function, each hook will be called in the order it was added with the event name and the tuple of arguments. Native hooks added by PySys_AddAuditHook() are called first, followed by hooks added in the current (sub)interpreter. Hooks can then log the event, raise an exception to abort the operation, or terminate the process entirely.

Note that audit hooks are primarily for collecting information about internal or otherwise unobservable actions, whether by Python or libraries written in Python. They are not suitable for implementing a "sandbox". In particular, malicious code can trivially disable or bypass hooks added using this function. At a minimum, any security-sensitive hooks must be added using the C API PySys_AddAuditHook() before initialising the runtime, and any modules allowing arbitrary memory modification (such as ctypes) should be completely removed or closely monitored.

呼叫 sys.addaudithook() 本身會引發一個不帶任何引數、名為 sys.addaudithook 的稽核事件。如果任何現有的 hook 引發從 RuntimeError 衍生的例外，則不會添加新的 hook 並抑制異常。因此，除非呼叫者控制所有已存在的 hook，他們不能假設他們的 hook 已被添加。

所有會被 CPython 所引發的事件請參考稽核事件總表、設計相關討論請見 PEP 578。

在 3.8 版被加入.

在 3.8.1 版的變更: Exceptions derived from Exception but not RuntimeError are no longer suppressed.

CPython 實作細節： When tracing is enabled (see settrace()), Python hooks are only traced if the callable has a __cantrace__ member that is set to a true value. Otherwise, trace functions will skip the hook.

sys.argv

The list of command line arguments passed to a Python script. argv[0] is the script name (it is operating system dependent whether this is a full pathname or not). If the command was executed using the -c command line option to the interpreter, argv[0] is set to the string '-c'. If no script name was passed to the Python interpreter, argv[0] is the empty string.

To loop over the standard input, or the list of files given on the command line, see the fileinput module.

另請參閱 sys.orig_argv。

備註

On Unix, command line arguments are passed by bytes from OS. Python decodes them with filesystem encoding and "surrogateescape" error handler. When you need original bytes, you can get it by [os.fsencode(arg) for arg in sys.argv].

sys.audit(event, *args)

Raise an auditing event and trigger any active auditing hooks. event is a string identifying the event, and args may contain optional arguments with more information about the event. The number and types of arguments for a given event are considered a public and stable API and should not be modified between releases.

舉例來說，一個名為 os.chdir 的稽核事件擁有一個引數 path，其內容為所要求的新工作目錄。

sys.audit() will call the existing auditing hooks, passing the event name and arguments, and will re-raise the first exception from any hook. In general, if an exception is raised, it should not be handled and the process should be terminated as quickly as possible. This allows hook implementations to decide how to respond to particular events: they can merely log the event or abort the operation by raising an exception.

Hooks are added using the sys.addaudithook() or PySys_AddAuditHook() functions.

The native equivalent of this function is PySys_Audit(). Using the native function is preferred when possible.

所有會被 CPython 所引發的事件請參考稽核事件總表。

在 3.8 版被加入.

sys.base_exec_prefix

Equivalent to exec_prefix, but referring to the base Python installation.

When running under 虛擬環境, exec_prefix gets overwritten to the virtual environment prefix. base_exec_prefix, conversely, does not change, and always points to the base Python installation. Refer to 虛擬環境 for more information.

在 3.3 版被加入.

sys.base_prefix

Equivalent to prefix, but referring to the base Python installation.

When running under virtual environment, prefix gets overwritten to the virtual environment prefix. base_prefix, conversely, does not change, and always points to the base Python installation. Refer to 虛擬環境 for more information.

在 3.3 版被加入.

sys.byteorder

An indicator of the native byte order. This will have the value 'big' on big-endian (most-significant byte first) platforms, and 'little' on little-endian (least-significant byte first) platforms.

sys.builtin_module_names

A tuple of strings containing the names of all modules that are compiled into this Python interpreter. (This information is not available in any other way --- modules.keys() only lists the imported modules.)

另請參閱 sys.stdlib_module_names 清單。

sys.call_tracing(func, args)

Call func(*args), while tracing is enabled. The tracing state is saved, and restored afterwards. This is intended to be called from a debugger from a checkpoint, to recursively debug or profile some other code.

Tracing is suspended while calling a tracing function set by settrace() or setprofile() to avoid infinite recursion. call_tracing() enables explicit recursion of the tracing function.

sys.copyright

A string containing the copyright pertaining to the Python interpreter.

sys._clear_type_cache()

Clear the internal type cache. The type cache is used to speed up attribute and method lookups. Use the function only to drop unnecessary references during reference leak debugging.

This function should be used for internal and specialized purposes only.

在 3.13 版之後被棄用: Use the more general _clear_internal_caches() function instead.

sys._clear_internal_caches()

Clear all internal performance-related caches. Use this function only to release unnecessary references and memory blocks when hunting for leaks.

在 3.13 版被加入.

sys._current_frames()

Return a dictionary mapping each thread's identifier to the topmost stack frame currently active in that thread at the time the function is called. Note that functions in the traceback module can build the call stack given such a frame.

This is most useful for debugging deadlock: this function does not require the deadlocked threads' cooperation, and such threads' call stacks are frozen for as long as they remain deadlocked. The frame returned for a non-deadlocked thread may bear no relationship to that thread's current activity by the time calling code examines the frame.

This function should be used for internal and specialized purposes only.

引發一個不附帶引數的稽核事件 sys._current_frames。

sys._current_exceptions()

Return a dictionary mapping each thread's identifier to the topmost exception currently active in that thread at the time the function is called. If a thread is not currently handling an exception, it is not included in the result dictionary.

This is most useful for statistical profiling.

This function should be used for internal and specialized purposes only.

引發一個不附帶引數的稽核事件 sys._current_exceptions。

在 3.12 版的變更: Each value in the dictionary is now a single exception instance, rather than a 3-tuple as returned from sys.exc_info().

sys.breakpointhook()

This hook function is called by built-in breakpoint(). By default, it drops you into the pdb debugger, but it can be set to any other function so that you can choose which debugger gets used.

The signature of this function is dependent on what it calls. For example, the default binding (e.g. pdb.set_trace()) expects no arguments, but you might bind it to a function that expects additional arguments (positional and/or keyword). The built-in breakpoint() function passes its *args and **kws straight through. Whatever breakpointhooks() returns is returned from breakpoint().

The default implementation first consults the environment variable PYTHONBREAKPOINT. If that is set to "0" then this function returns immediately; i.e. it is a no-op. If the environment variable is not set, or is set to the empty string, pdb.set_trace() is called. Otherwise this variable should name a function to run, using Python's dotted-import nomenclature, e.g. package.subpackage.module.function. In this case, package.subpackage.module would be imported and the resulting module must have a callable named function(). This is run, passing in *args and **kws, and whatever function() returns, sys.breakpointhook() returns to the built-in breakpoint() function.

Note that if anything goes wrong while importing the callable named by PYTHONBREAKPOINT, a RuntimeWarning is reported and the breakpoint is ignored.

Also note that if sys.breakpointhook() is overridden programmatically, PYTHONBREAKPOINT is not consulted.

在 3.7 版被加入.

sys._debugmallocstats()

Print low-level information to stderr about the state of CPython's memory allocator.

If Python is built in debug mode (configure --with-pydebug option), it also performs some expensive internal consistency checks.

在 3.3 版被加入.

CPython 實作細節： This function is specific to CPython. The exact output format is not defined here, and may change.

sys.dllhandle

Integer specifying the handle of the Python DLL.

可用性: Windows.

sys.displayhook(value)

If value is not None, this function prints repr(value) to sys.stdout, and saves value in builtins._. If repr(value) is not encodable to sys.stdout.encoding with sys.stdout.errors error handler (which is probably 'strict'), encode it to sys.stdout.encoding with 'backslashreplace' error handler.

sys.displayhook is called on the result of evaluating an expression entered in an interactive Python session. The display of these values can be customized by assigning another one-argument function to sys.displayhook.

Pseudo-code:

def displayhook(value):
    if value is None:
        return
    # Set '_' to None to avoid recursion
    builtins._ = None
    text = repr(value)
    try:
        sys.stdout.write(text)
    except UnicodeEncodeError:
        bytes = text.encode(sys.stdout.encoding, 'backslashreplace')
        if hasattr(sys.stdout, 'buffer'):
            sys.stdout.buffer.write(bytes)
        else:
            text = bytes.decode(sys.stdout.encoding, 'strict')
            sys.stdout.write(text)
    sys.stdout.write("\n")
    builtins._ = value

在 3.2 版的變更: Use 'backslashreplace' error handler on UnicodeEncodeError.

sys.dont_write_bytecode

If this is true, Python won't try to write .pyc files on the import of source modules. This value is initially set to True or False depending on the -B command line option and the PYTHONDONTWRITEBYTECODE environment variable, but you can set it yourself to control bytecode file generation.

sys._emscripten_info

A named tuple holding information about the environment on the wasm32-emscripten platform. The named tuple is provisional and may change in the future.

_emscripten_info.emscripten_version

Emscripten version as tuple of ints (major, minor, micro), e.g. (3, 1, 8).

_emscripten_info.runtime

運行環境字串，例如瀏覽器使用者代理 (browser user agent) 'Node.js v14.18.2' 或 'UNKNOWN'。

_emscripten_info.pthreads

True if Python is compiled with Emscripten pthreads support.

_emscripten_info.shared_memory

True if Python is compiled with shared memory support.

可用性: Emscripten.

在 3.11 版被加入.

sys.pycache_prefix

If this is set (not None), Python will write bytecode-cache .pyc files to (and read them from) a parallel directory tree rooted at this directory, rather than from __pycache__ directories in the source code tree. Any __pycache__ directories in the source code tree will be ignored and new .pyc files written within the pycache prefix. Thus if you use compileall as a pre-build step, you must ensure you run it with the same pycache prefix (if any) that you will use at runtime.

A relative path is interpreted relative to the current working directory.

This value is initially set based on the value of the -X pycache_prefix=PATH command-line option or the PYTHONPYCACHEPREFIX environment variable (command-line takes precedence). If neither are set, it is None.

在 3.8 版被加入.

sys.excepthook(type, value, traceback)

This function prints out a given traceback and exception to sys.stderr.

When an exception other than SystemExit is raised and uncaught, the interpreter calls sys.excepthook with three arguments, the exception class, exception instance, and a traceback object. In an interactive session this happens just before control is returned to the prompt; in a Python program this happens just before the program exits. The handling of such top-level exceptions can be customized by assigning another three-argument function to sys.excepthook.

Raise an auditing event sys.excepthook with arguments hook, type, value, traceback when an uncaught exception occurs. If no hook has been set, hook may be None. If any hook raises an exception derived from RuntimeError the call to the hook will be suppressed. Otherwise, the audit hook exception will be reported as unraisable and sys.excepthook will be called.

也參考

The sys.unraisablehook() function handles unraisable exceptions and the threading.excepthook() function handles exception raised by threading.Thread.run().

sys.__breakpointhook__

sys.__displayhook__

sys.__excepthook__

sys.__unraisablehook__

These objects contain the original values of breakpointhook, displayhook, excepthook, and unraisablehook at the start of the program. They are saved so that breakpointhook, displayhook and excepthook, unraisablehook can be restored in case they happen to get replaced with broken or alternative objects.

在 3.7 版被加入: __breakpointhook__

在 3.8 版被加入: __unraisablehook__

sys.exception()

This function, when called while an exception handler is executing (such as an except or except* clause), returns the exception instance that was caught by this handler. When exception handlers are nested within one another, only the exception handled by the innermost handler is accessible.

If no exception handler is executing, this function returns None.

在 3.11 版被加入.

sys.exc_info()

This function returns the old-style representation of the handled exception. If an exception e is currently handled (so exception() would return e), exc_info() returns the tuple (type(e), e, e.__traceback__). That is, a tuple containing the type of the exception (a subclass of BaseException), the exception itself, and a traceback object which typically encapsulates the call stack at the point where the exception last occurred.

If no exception is being handled anywhere on the stack, this function return a tuple containing three None values.

在 3.11 版的變更: The type and traceback fields are now derived from the value (the exception instance), so when an exception is modified while it is being handled, the changes are reflected in the results of subsequent calls to exc_info().

sys.exec_prefix

A string giving the site-specific directory prefix where the platform-dependent Python files are installed; by default, this is also '/usr/local'. This can be set at build time with the --exec-prefix argument to the configure script. Specifically, all configuration files (e.g. the pyconfig.h header file) are installed in the directory exec_prefix/lib/pythonX.Y/config, and shared library modules are installed in exec_prefix/lib/pythonX.Y/lib-dynload, where X.Y is the version number of Python, for example 3.2.

備註

If a virtual environment is in effect, this exec_prefix will point to the virtual environment. The value for the Python installation will still be available, via base_exec_prefix. Refer to 虛擬環境 for more information.

在 3.14 版的變更: When running under a virtual environment, prefix and exec_prefix are now set to the virtual environment prefix by the path initialization, instead of site. This means that prefix and exec_prefix always point to the virtual environment, even when site is disabled (-S).

sys.executable

A string giving the absolute path of the executable binary for the Python interpreter, on systems where this makes sense. If Python is unable to retrieve the real path to its executable, sys.executable will be an empty string or None.

sys.exit([arg])

Raise a SystemExit exception, signaling an intention to exit the interpreter.

The optional argument arg can be an integer giving the exit status (defaulting to zero), or another type of object. If it is an integer, zero is considered "successful termination" and any nonzero value is considered "abnormal termination" by shells and the like. Most systems require it to be in the range 0--127, and produce undefined results otherwise. Some systems have a convention for assigning specific meanings to specific exit codes, but these are generally underdeveloped; Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors. If another type of object is passed, None is equivalent to passing zero, and any other object is printed to stderr and results in an exit code of 1. In particular, sys.exit("some error message") is a quick way to exit a program when an error occurs.

Since exit() ultimately "only" raises an exception, it will only exit the process when called from the main thread, and the exception is not intercepted. Cleanup actions specified by finally clauses of try statements are honored, and it is possible to intercept the exit attempt at an outer level.

在 3.6 版的變更: If an error occurs in the cleanup after the Python interpreter has caught SystemExit (such as an error flushing buffered data in the standard streams), the exit status is changed to 120.

sys.flags

The named tuple flags exposes the status of command line flags. Flags should only be accessed only by name and not by index. The attributes are read only.

flags.debug	-d
flags.inspect	-i
flags.interactive	-i
flags.isolated	-I
flags.optimize	-O 或 -OO
flags.dont_write_bytecode	-B
flags.no_user_site	-s
flags.no_site	-S
flags.ignore_environment	-E
flags.verbose	-v
flags.bytes_warning	-b
flags.quiet	-q
flags.hash_randomization	-R
flags.dev_mode	-X dev （Python 開發模式）
flags.utf8_mode	-X utf8
flags.safe_path	-P
flags.int_max_str_digits	-X int_max_str_digits (integer string conversion length limitation)
flags.warn_default_encoding	-X warn_default_encoding
flags.gil	-X gil and PYTHON_GIL
flags.thread_inherit_context	-X thread_inherit_context and PYTHON_THREAD_INHERIT_CONTEXT
flags.context_aware_warnings	-X context_aware_warnings and PYTHON_CONTEXT_AWARE_WARNINGS

在 3.2 版的變更: 新增 quiet 屬性，用於新的 -q 旗標。

在 3.2.3 版被加入: hash_randomization 屬性。

在 3.3 版的變更: 移除過時的 division_warning 屬性。

在 3.4 版的變更: 新增 isolated 屬性，用於 -I isolated 旗標。

在 3.7 版的變更: Added the dev_mode attribute for the new Python Development Mode and the utf8_mode attribute for the new -X utf8 flag.

在 3.10 版的變更: 新增 warn_default_encoding 屬性，用於 -X warn_default_encoding 旗標。

在 3.11 版的變更: 新增 safe_path 屬性，用於 -P 選項。

在 3.11 版的變更: 新增 int_max_str_digits 屬性。

在 3.13 版的變更: 新增 gil 屬性。

在 3.14 版的變更: 新增 thread_inherit_context 屬性。

在 3.14 版的變更: 新增 context_aware_warnings 屬性。

sys.float_info

A named tuple holding information about the float type. It contains low level information about the precision and internal representation. The values correspond to the various floating-point constants defined in the standard header file float.h for the 'C' programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard [C99], 'Characteristics of floating types', for details.

Attributes of the float_info named tuple

屬性	float.h macro	解釋
float_info.epsilon	DBL_EPSILON	difference between 1.0 and the least value greater than 1.0 that is representable as a float. 另請參閱 math.ulp()。
float_info.dig	DBL_DIG	The maximum number of decimal digits that can be faithfully represented in a float; see below.
float_info.mant_dig	DBL_MANT_DIG	Float precision: the number of base-radix digits in the significand of a float.
float_info.max	DBL_MAX	The maximum representable positive finite float.
float_info.max_exp	DBL_MAX_EXP	The maximum integer e such that radix**(e-1) is a representable finite float.
float_info.max_10_exp	DBL_MAX_10_EXP	The maximum integer e such that 10**e is in the range of representable finite floats.
float_info.min	DBL_MIN	The minimum representable positive normalized float. Use math.ulp(0.0) to get the smallest positive denormalized representable float.
float_info.min_exp	DBL_MIN_EXP	The minimum integer e such that radix**(e-1) is a normalized float.
float_info.min_10_exp	DBL_MIN_10_EXP	The minimum integer e such that 10**e is a normalized float.
float_info.radix	FLT_RADIX	The radix of exponent representation.
float_info.rounds	FLT_ROUNDS	An integer representing the rounding mode for floating-point arithmetic. This reflects the value of the system FLT_ROUNDS macro at interpreter startup time: -1: indeterminable 0: toward zero 1: to nearest 2: toward positive infinity 3: toward negative infinity All other values for FLT_ROUNDS characterize implementation-defined rounding behavior.

The attribute sys.float_info.dig needs further explanation. If s is any string representing a decimal number with at most sys.float_info.dig significant digits, then converting s to a float and back again will recover a string representing the same decimal value:

>>> import sys
>>> sys.float_info.dig
15
>>> s = '3.14159265358979'    # decimal string with 15 significant digits
>>> format(float(s), '.15g')  # convert to float and back -> same value
'3.14159265358979'

But for strings with more than sys.float_info.dig significant digits, this isn't always true:

>>> s = '9876543211234567'    # 16 significant digits is too many!
>>> format(float(s), '.16g')  # conversion changes value
'9876543211234568'

sys.float_repr_style

A string indicating how the repr() function behaves for floats. If the string has value 'short' then for a finite float x, repr(x) aims to produce a short string with the property that float(repr(x)) == x. This is the usual behaviour in Python 3.1 and later. Otherwise, float_repr_style has value 'legacy' and repr(x) behaves in the same way as it did in versions of Python prior to 3.1.

在 3.1 版被加入.

sys.getallocatedblocks()

Return the number of memory blocks currently allocated by the interpreter, regardless of their size. This function is mainly useful for tracking and debugging memory leaks. Because of the interpreter's internal caches, the result can vary from call to call; you may have to call _clear_internal_caches() and gc.collect() to get more predictable results.

If a Python build or implementation cannot reasonably compute this information, getallocatedblocks() is allowed to return 0 instead.

在 3.4 版被加入.

sys.getunicodeinternedsize()

Return the number of unicode objects that have been interned.

在 3.12 版被加入.

sys.getandroidapilevel()

Return the build-time API level of Android as an integer. This represents the minimum version of Android this build of Python can run on. For runtime version information, see platform.android_ver().

可用性: Android.

在 3.7 版被加入.

sys.getdefaultencoding()

Return 'utf-8'. This is the name of the default string encoding, used in methods like str.encode().

sys.getdlopenflags()

Return the current value of the flags that are used for dlopen() calls. Symbolic names for the flag values can be found in the os module (RTLD_xxx constants, e.g. os.RTLD_LAZY).

可用性: Unix.

sys.getfilesystemencoding()

Get the filesystem encoding: the encoding used with the filesystem error handler to convert between Unicode filenames and bytes filenames. The filesystem error handler is returned from getfilesystemencodeerrors().

For best compatibility, str should be used for filenames in all cases, although representing filenames as bytes is also supported. Functions accepting or returning filenames should support either str or bytes and internally convert to the system's preferred representation.

os.fsencode() and os.fsdecode() should be used to ensure that the correct encoding and errors mode are used.

The filesystem encoding and error handler are configured at Python startup by the PyConfig_Read() function: see filesystem_encoding and filesystem_errors members of PyConfig.

在 3.2 版的變更: getfilesystemencoding() 的結果不再為 None。

在 3.6 版的變更: Windows is no longer guaranteed to return 'mbcs'. See PEP 529 and _enablelegacywindowsfsencoding() for more information.

在 3.7 版的變更: Return 'utf-8' if the Python UTF-8 Mode is enabled.

sys.getfilesystemencodeerrors()

Get the filesystem error handler: the error handler used with the filesystem encoding to convert between Unicode filenames and bytes filenames. The filesystem encoding is returned from getfilesystemencoding().

os.fsencode() and os.fsdecode() should be used to ensure that the correct encoding and errors mode are used.

The filesystem encoding and error handler are configured at Python startup by the PyConfig_Read() function: see filesystem_encoding and filesystem_errors members of PyConfig.

在 3.6 版被加入.

sys.get_int_max_str_digits()

Returns the current value for the integer string conversion length limitation. See also set_int_max_str_digits().

在 3.11 版被加入.

sys.getrefcount(object)

Return the reference count of the object. The count returned is generally one higher than you might expect, because it includes the (temporary) reference as an argument to getrefcount().

Note that the returned value may not actually reflect how many references to the object are actually held. For example, some objects are immortal and have a very high refcount that does not reflect the actual number of references. Consequently, do not rely on the returned value to be accurate, other than a value of 0 or 1.

CPython 實作細節： Immortal objects with a large reference count can be identified via _is_immortal().

在 3.12 版的變更: Immortal objects have very large refcounts that do not match the actual number of references to the object.

sys.getrecursionlimit()

Return the current value of the recursion limit, the maximum depth of the Python interpreter stack. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python. It can be set by setrecursionlimit().

sys.getsizeof(object[, default])

Return the size of an object in bytes. The object can be any type of object. All built-in objects will return correct results, but this does not have to hold true for third-party extensions as it is implementation specific.

Only the memory consumption directly attributed to the object is accounted for, not the memory consumption of objects it refers to.

If given, default will be returned if the object does not provide means to retrieve the size. Otherwise a TypeError will be raised.

getsizeof() calls the object's __sizeof__ method and adds an additional garbage collector overhead if the object is managed by the garbage collector.

See recursive sizeof recipe for an example of using getsizeof() recursively to find the size of containers and all their contents.

sys.getswitchinterval()

Return the interpreter's "thread switch interval" in seconds; see setswitchinterval().

在 3.2 版被加入.

sys._getframe([depth])

Return a frame object from the call stack. If optional integer depth is given, return the frame object that many calls below the top of the stack. If that is deeper than the call stack, ValueError is raised. The default for depth is zero, returning the frame at the top of the call stack.

引發一個附帶引數 frame 的稽核事件 sys._getframe。

CPython 實作細節： This function should be used for internal and specialized purposes only. It is not guaranteed to exist in all implementations of Python.

sys._getframemodulename([depth])

Return the name of a module from the call stack. If optional integer depth is given, return the module that many calls below the top of the stack. If that is deeper than the call stack, or if the module is unidentifiable, None is returned. The default for depth is zero, returning the module at the top of the call stack.

引發一個附帶引數 depth 的稽核事件 sys._getframemodulename。

CPython 實作細節： This function should be used for internal and specialized purposes only. It is not guaranteed to exist in all implementations of Python.

在 3.12 版被加入.

sys.getobjects(limit[, type])

This function only exists if CPython was built using the specialized configure option --with-trace-refs. It is intended only for debugging garbage-collection issues.

Return a list of up to limit dynamically allocated Python objects. If type is given, only objects of that exact type (not subtypes) are included.

Objects from the list are not safe to use. Specifically, the result will include objects from all interpreters that share their object allocator state (that is, ones created with PyInterpreterConfig.use_main_obmalloc set to 1 or using Py_NewInterpreter(), and the main interpreter). Mixing objects from different interpreters may lead to crashes or other unexpected behavior.

CPython 實作細節： This function should be used for specialized purposes only. It is not guaranteed to exist in all implementations of Python.

在 3.14 版的變更: The result may include objects from other interpreters.

sys.getprofile()

Get the profiler function as set by setprofile().

sys.gettrace()

Get the trace function as set by settrace().

CPython 實作細節： The gettrace() function is intended only for implementing debuggers, profilers, coverage tools and the like. Its behavior is part of the implementation platform, rather than part of the language definition, and thus may not be available in all Python implementations.

sys.getwindowsversion()

Return a named tuple describing the Windows version currently running. The named elements are major, minor, build, platform, service_pack, service_pack_minor, service_pack_major, suite_mask, product_type and platform_version. service_pack contains a string, platform_version a 3-tuple and all other values are integers. The components can also be accessed by name, so sys.getwindowsversion()[0] is equivalent to sys.getwindowsversion().major. For compatibility with prior versions, only the first 5 elements are retrievable by indexing.

platform will be 2 (VER_PLATFORM_WIN32_NT).

product_type may be one of the following values:

Constant	含義
1 (VER_NT_WORKSTATION)	The system is a workstation.
2 (VER_NT_DOMAIN_CONTROLLER)	The system is a domain controller.
3 (VER_NT_SERVER)	The system is a server, but not a domain controller.

This function wraps the Win32 GetVersionEx() function; see the Microsoft documentation on OSVERSIONINFOEX() for more information about these fields.

platform_version returns the major version, minor version and build number of the current operating system, rather than the version that is being emulated for the process. It is intended for use in logging rather than for feature detection.

備註

platform_version derives the version from kernel32.dll which can be of a different version than the OS version. Please use platform module for achieving accurate OS version.

可用性: Windows.

在 3.2 版的變更: Changed to a named tuple and added service_pack_minor, service_pack_major, suite_mask, and product_type.

在 3.6 版的變更: 新增 platform_version

sys.get_asyncgen_hooks()

Returns an asyncgen_hooks object, which is similar to a namedtuple of the form (firstiter, finalizer), where firstiter and finalizer are expected to be either None or functions which take an asynchronous generator iterator as an argument, and are used to schedule finalization of an asynchronous generator by an event loop.

在 3.6 版被加入: 更多細節請見 PEP 525。

備註

This function has been added on a provisional basis (see PEP 411 for details.)

sys.get_coroutine_origin_tracking_depth()

Get the current coroutine origin tracking depth, as set by set_coroutine_origin_tracking_depth().

在 3.7 版被加入.

備註

This function has been added on a provisional basis (see PEP 411 for details.) Use it only for debugging purposes.

sys.hash_info

A named tuple giving parameters of the numeric hash implementation. For more details about hashing of numeric types, see 數值型別的雜湊.

hash_info.width

The width in bits used for hash values

hash_info.modulus

The prime modulus P used for numeric hash scheme

hash_info.inf

The hash value returned for a positive infinity

hash_info.nan

(This attribute is no longer used)

hash_info.imag

The multiplier used for the imaginary part of a complex number

hash_info.algorithm

The name of the algorithm for hashing of str, bytes, and memoryview

hash_info.hash_bits

The internal output size of the hash algorithm

hash_info.seed_bits

The size of the seed key of the hash algorithm

在 3.2 版被加入.

在 3.4 版的變更: 新增 algorithm、hash_bits 與 seed_bits

sys.hexversion

The version number encoded as a single integer. This is guaranteed to increase with each version, including proper support for non-production releases. For example, to test that the Python interpreter is at least version 1.5.2, use:

if sys.hexversion >= 0x010502F0:
    # use some advanced feature
    ...
else:
    # use an alternative implementation or warn the user
    ...

This is called hexversion since it only really looks meaningful when viewed as the result of passing it to the built-in hex() function. The named tuple sys.version_info may be used for a more human-friendly encoding of the same information.

More details of hexversion can be found at API 和 ABI 版本管理.

sys.implementation

An object containing information about the implementation of the currently running Python interpreter. The following attributes are required to exist in all Python implementations.

name is the implementation's identifier, e.g. 'cpython'. The actual string is defined by the Python implementation, but it is guaranteed to be lower case.

version is a named tuple, in the same format as sys.version_info. It represents the version of the Python implementation. This has a distinct meaning from the specific version of the Python language to which the currently running interpreter conforms, which sys.version_info represents. For example, for PyPy 1.8 sys.implementation.version might be sys.version_info(1, 8, 0, 'final', 0), whereas sys.version_info would be sys.version_info(2, 7, 2, 'final', 0). For CPython they are the same value, since it is the reference implementation.

hexversion is the implementation version in hexadecimal format, like sys.hexversion.

cache_tag is the tag used by the import machinery in the filenames of cached modules. By convention, it would be a composite of the implementation's name and version, like 'cpython-33'. However, a Python implementation may use some other value if appropriate. If cache_tag is set to None, it indicates that module caching should be disabled.

supports_isolated_interpreters is a boolean value, whether this implementation supports multiple isolated interpreters. It is True for CPython on most platforms. Platforms with this support implement the low-level _interpreters module.

也參考

PEP 684, PEP 734, and concurrent.interpreters.

sys.implementation may contain additional attributes specific to the Python implementation. These non-standard attributes must start with an underscore, and are not described here. Regardless of its contents, sys.implementation will not change during a run of the interpreter, nor between implementation versions. (It may change between Python language versions, however.) See PEP 421 for more information.

在 3.3 版被加入.

在 3.14 版的變更: Added supports_isolated_interpreters field.

備註

The addition of new required attributes must go through the normal PEP process. See PEP 421 for more information.

sys.int_info

A named tuple that holds information about Python's internal representation of integers. The attributes are read only.

int_info.bits_per_digit

The number of bits held in each digit. Python integers are stored internally in base 2**int_info.bits_per_digit.

int_info.sizeof_digit

The size in bytes of the C type used to represent a digit.

int_info.default_max_str_digits

The default value for sys.get_int_max_str_digits() when it is not otherwise explicitly configured.

int_info.str_digits_check_threshold

The minimum non-zero value for sys.set_int_max_str_digits(), PYTHONINTMAXSTRDIGITS, or -X int_max_str_digits.

在 3.1 版被加入.

在 3.11 版的變更: 新增 default_max_str_digits 和 str_digits_check_threshold。

sys.__interactivehook__

When this attribute exists, its value is automatically called (with no arguments) when the interpreter is launched in interactive mode. This is done after the PYTHONSTARTUP file is read, so that you can set this hook there. The site module sets this.

Raises an auditing event cpython.run_interactivehook with the hook object as the argument when the hook is called on startup.

在 3.4 版被加入.

sys.intern(string)

Enter string in the table of "interned" strings and return the interned string -- which is string itself or a copy. Interning strings is useful to gain a little performance on dictionary lookup -- if the keys in a dictionary are interned, and the lookup key is interned, the key comparisons (after hashing) can be done by a pointer compare instead of a string compare. Normally, the names used in Python programs are automatically interned, and the dictionaries used to hold module, class or instance attributes have interned keys.

Interned strings are not immortal; you must keep a reference to the return value of intern() around to benefit from it.

sys._is_gil_enabled()

Return True if the GIL is enabled and False if it is disabled.

在 3.13 版被加入.

CPython 實作細節： It is not guaranteed to exist in all implementations of Python.

sys.is_finalizing()

Return True if the main Python interpreter is shutting down. Return False otherwise.

另請參閱 PythonFinalizationError 例外。

在 3.5 版被加入.

sys._jit

Utilities for observing just-in-time compilation.

CPython 實作細節： JIT compilation is an experimental implementation detail of CPython. sys._jit is not guaranteed to exist or behave the same way in all Python implementations, versions, or build configurations.

在 3.14 版被加入.

_jit.is_available()

Return True if the current Python executable supports JIT compilation, and False otherwise. This can be controlled by building CPython with the --experimental-jit option on Windows, and the --enable-experimental-jit option on all other platforms.

_jit.is_enabled()

Return True if JIT compilation is enabled for the current Python process (implies sys._jit.is_available()), and False otherwise. If JIT compilation is available, this can be controlled by setting the PYTHON_JIT environment variable to 0 (disabled) or 1 (enabled) at interpreter startup.

_jit.is_active()

Return True if the topmost Python frame is currently executing JIT code (implies sys._jit.is_enabled()), and False otherwise.

備註

This function is intended for testing and debugging the JIT itself. It should be avoided for any other purpose.

備註

Due to the nature of tracing JIT compilers, repeated calls to this function may give surprising results. For example, branching on its return value will likely lead to unexpected behavior (if doing so causes JIT code to be entered or exited):

>>> for warmup in range(BIG_NUMBER):
...     # This line is "hot", and is eventually JIT-compiled:
...     if sys._jit.is_active():
...         # This line is "cold", and is run in the interpreter:
...         assert sys._jit.is_active()
...
Traceback (most recent call last):
  File "<stdin>", line 5, in <module>
    assert sys._jit.is_active()
           ~~~~~~~~~~~~~~~~~~^^
AssertionError

sys.last_exc

This variable is not always defined; it is set to the exception instance when an exception is not handled and the interpreter prints an error message and a stack traceback. Its intended use is to allow an interactive user to import a debugger module and engage in post-mortem debugging without having to re-execute the command that caused the error. (Typical use is import pdb; pdb.pm() to enter the post-mortem debugger; see pdb module for more information.)

在 3.12 版被加入.

sys._is_immortal(op)

Return True if the given object is immortal, False otherwise.

備註

Objects that are immortal (and thus return True upon being passed to this function) are not guaranteed to be immortal in future versions, and vice versa for mortal objects.

在 3.14 版被加入.

CPython 實作細節： This function should be used for specialized purposes only. It is not guaranteed to exist in all implementations of Python.

sys._is_interned(string)

Return True if the given string is "interned", False otherwise.

在 3.13 版被加入.

CPython 實作細節： It is not guaranteed to exist in all implementations of Python.

sys.last_type

sys.last_value

sys.last_traceback

These three variables are deprecated; use sys.last_exc instead. They hold the legacy representation of sys.last_exc, as returned from exc_info() above.

sys.maxsize

An integer giving the maximum value a variable of type Py_ssize_t can take. It's usually 2**31 - 1 on a 32-bit platform and 2**63 - 1 on a 64-bit platform.

sys.maxunicode

An integer giving the value of the largest Unicode code point, i.e. 1114111 (0x10FFFF in hexadecimal).

在 3.3 版的變更: Before PEP 393, sys.maxunicode used to be either 0xFFFF or 0x10FFFF, depending on the configuration option that specified whether Unicode characters were stored as UCS-2 or UCS-4.

sys.meta_path

A list of meta path finder objects that have their find_spec() methods called to see if one of the objects can find the module to be imported. By default, it holds entries that implement Python's default import semantics. The find_spec() method is called with at least the absolute name of the module being imported. If the module to be imported is contained in a package, then the parent package's __path__ attribute is passed in as a second argument. The method returns a module spec, or None if the module cannot be found.

也參考

importlib.abc.MetaPathFinder

The abstract base class defining the interface of finder objects on meta_path.

importlib.machinery.ModuleSpec

The concrete class which find_spec() should return instances of.

在 3.4 版的變更: Module specs were introduced in Python 3.4, by PEP 451.

在 3.12 版的變更: Removed the fallback that looked for a find_module() method if a meta_path entry didn't have a find_spec() method.

sys.modules

This is a dictionary that maps module names to modules which have already been loaded. This can be manipulated to force reloading of modules and other tricks. However, replacing the dictionary will not necessarily work as expected and deleting essential items from the dictionary may cause Python to fail. If you want to iterate over this global dictionary always use sys.modules.copy() or tuple(sys.modules) to avoid exceptions as its size may change during iteration as a side effect of code or activity in other threads.

sys.orig_argv

The list of the original command line arguments passed to the Python executable.

The elements of sys.orig_argv are the arguments to the Python interpreter, while the elements of sys.argv are the arguments to the user's program. Arguments consumed by the interpreter itself will be present in sys.orig_argv and missing from sys.argv.

在 3.10 版被加入.

sys.path

A list of strings that specifies the search path for modules. Initialized from the environment variable PYTHONPATH, plus an installation-dependent default.

By default, as initialized upon program startup, a potentially unsafe path is prepended to sys.path (before the entries inserted as a result of PYTHONPATH):

• python -m module command line: prepend the current working directory.

• python script.py command line: prepend the script's directory. If it's a symbolic link, resolve symbolic links.

• python -c code and python (REPL) command lines: prepend an empty string, which means the current working directory.

To not prepend this potentially unsafe path, use the -P command line option or the PYTHONSAFEPATH environment variable.

A program is free to modify this list for its own purposes. Only strings should be added to sys.path; all other data types are ignored during import.

也參考

• Module site This describes how to use .pth files to extend sys.path.

sys.path_hooks

A list of callables that take a path argument to try to create a finder for the path. If a finder can be created, it is to be returned by the callable, else raise ImportError.

Originally specified in PEP 302.

sys.path_importer_cache

A dictionary acting as a cache for finder objects. The keys are paths that have been passed to sys.path_hooks and the values are the finders that are found. If a path is a valid file system path but no finder is found on sys.path_hooks then None is stored.

Originally specified in PEP 302.

sys.platform

A string containing a platform identifier. Known values are:

系統	platform 值
AIX	'aix'
Android	'android'
Emscripten	'emscripten'
FreeBSD	'freebsd'
iOS	'ios'
Linux	'linux'
macOS	'darwin'
Windows	'win32'
Windows/Cygwin	'cygwin'
WASI	'wasi'

On Unix systems not listed in the table, the value is the lowercased OS name as returned by uname -s, with the first part of the version as returned by uname -r appended, e.g. 'sunos5', at the time when Python was built. Unless you want to test for a specific system version, it is therefore recommended to use the following idiom:

if sys.platform.startswith('sunos'):
    # 這裡會是 SunOS 專屬的程式碼...

在 3.3 版的變更: On Linux, sys.platform doesn't contain the major version anymore. It is always 'linux', instead of 'linux2' or 'linux3'.

在 3.8 版的變更: On AIX, sys.platform doesn't contain the major version anymore. It is always 'aix', instead of 'aix5' or 'aix7'.

在 3.13 版的變更: On Android, sys.platform now returns 'android' rather than 'linux'.

在 3.14 版的變更: On FreeBSD, sys.platform doesn't contain the major version anymore. It is always 'freebsd', instead of 'freebsd13' or 'freebsd14'.

也參考

os.name has a coarser granularity. os.uname() gives system-dependent version information.

The platform module provides detailed checks for the system's identity.

sys.platlibdir

Name of the platform-specific library directory. It is used to build the path of standard library and the paths of installed extension modules.

It is equal to "lib" on most platforms. On Fedora and SuSE, it is equal to "lib64" on 64-bit platforms which gives the following sys.path paths (where X.Y is the Python major.minor version):

• /usr/lib64/pythonX.Y/: Standard library (like os.py of the os module)

• /usr/lib64/pythonX.Y/lib-dynload/: C extension modules of the standard library (like the errno module, the exact filename is platform specific)

• /usr/lib/pythonX.Y/site-packages/ (always use lib, not sys.platlibdir): Third-party modules

• /usr/lib64/pythonX.Y/site-packages/: C extension modules of third-party packages

在 3.9 版被加入.

sys.prefix

A string giving the site-specific directory prefix where the platform independent Python files are installed; on Unix, the default is /usr/local. This can be set at build time with the --prefix argument to the configure script. See Installation paths for derived paths.

備註

If a virtual environment is in effect, this prefix will point to the virtual environment. The value for the Python installation will still be available, via base_prefix. Refer to 虛擬環境 for more information.

在 3.14 版的變更: When running under a virtual environment, prefix and exec_prefix are now set to the virtual environment prefix by the path initialization, instead of site. This means that prefix and exec_prefix always point to the virtual environment, even when site is disabled (-S).

sys.ps1

sys.ps2

Strings specifying the primary and secondary prompt of the interpreter. These are only defined if the interpreter is in interactive mode. Their initial values in this case are '>>> ' and '... '. If a non-string object is assigned to either variable, its str() is re-evaluated each time the interpreter prepares to read a new interactive command; this can be used to implement a dynamic prompt.

sys.setdlopenflags(n)

Set the flags used by the interpreter for dlopen() calls, such as when the interpreter loads extension modules. Among other things, this will enable a lazy resolving of symbols when importing a module, if called as sys.setdlopenflags(0). To share symbols across extension modules, call as sys.setdlopenflags(os.RTLD_GLOBAL). Symbolic names for the flag values can be found in the os module (RTLD_xxx constants, e.g. os.RTLD_LAZY).

可用性: Unix.

sys.set_int_max_str_digits(maxdigits)

Set the integer string conversion length limitation used by this interpreter. See also get_int_max_str_digits().

在 3.11 版被加入.

sys.setprofile(profilefunc)

Set the system's profile function, which allows you to implement a Python source code profiler in Python. See chapter Python 的分析器 for more information on the Python profiler. The system's profile function is called similarly to the system's trace function (see settrace()), but it is called with different events, for example it isn't called for each executed line of code (only on call and return, but the return event is reported even when an exception has been set). The function is thread-specific, but there is no way for the profiler to know about context switches between threads, so it does not make sense to use this in the presence of multiple threads. Also, its return value is not used, so it can simply return None. Error in the profile function will cause itself unset.

備註

The same tracing mechanism is used for setprofile() as settrace(). To trace calls with setprofile() inside a tracing function (e.g. in a debugger breakpoint), see call_tracing().

Profile functions should have three arguments: frame, event, and arg. frame is the current stack frame. event is a string: 'call', 'return', 'c_call', 'c_return', or 'c_exception'. arg depends on the event type.

The events have the following meaning:

'call'

A function is called (or some other code block entered). The profile function is called; arg is None.

'return'

A function (or other code block) is about to return. The profile function is called; arg is the value that will be returned, or None if the event is caused by an exception being raised.

'c_call'

A C function is about to be called. This may be an extension function or a built-in. arg is the C function object.

'c_return'

A C function has returned. arg is the C function object.

'c_exception'

A C function has raised an exception. arg is the C function object.

引發一個不附帶引數的稽核事件 sys.setprofile。

sys.setrecursionlimit(limit)

Set the maximum depth of the Python interpreter stack to limit. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python.

The highest possible limit is platform-dependent. A user may need to set the limit higher when they have a program that requires deep recursion and a platform that supports a higher limit. This should be done with care, because a too-high limit can lead to a crash.

If the new limit is too low at the current recursion depth, a RecursionError exception is raised.

在 3.5.1 版的變更: A RecursionError exception is now raised if the new limit is too low at the current recursion depth.

sys.setswitchinterval(interval)

Set the interpreter's thread switch interval (in seconds). This floating-point value determines the ideal duration of the "timeslices" allocated to concurrently running Python threads. Please note that the actual value can be higher, especially if long-running internal functions or methods are used. Also, which thread becomes scheduled at the end of the interval is the operating system's decision. The interpreter doesn't have its own scheduler.

在 3.2 版被加入.

sys.settrace(tracefunc)

Set the system's trace function, which allows you to implement a Python source code debugger in Python. The function is thread-specific; for a debugger to support multiple threads, it must register a trace function using settrace() for each thread being debugged or use threading.settrace().

Trace functions should have three arguments: frame, event, and arg. frame is the current stack frame. event is a string: 'call', 'line', 'return', 'exception' or 'opcode'. arg depends on the event type.

The trace function is invoked (with event set to 'call') whenever a new local scope is entered; it should return a reference to a local trace function to be used for the new scope, or None if the scope shouldn't be traced.

The local trace function should return a reference to itself, or to another function which would then be used as the local trace function for the scope.

If there is any error occurred in the trace function, it will be unset, just like settrace(None) is called.

備註

Tracing is disabled while calling the trace function (e.g. a function set by settrace()). For recursive tracing see call_tracing().

The events have the following meaning:

'call'

A function is called (or some other code block entered). The global trace function is called; arg is None; the return value specifies the local trace function.

'line'

The interpreter is about to execute a new line of code or re-execute the condition of a loop. The local trace function is called; arg is None; the return value specifies the new local trace function. See Objects/lnotab_notes.txt for a detailed explanation of how this works. Per-line events may be disabled for a frame by setting f_trace_lines to False on that frame.

'return'

A function (or other code block) is about to return. The local trace function is called; arg is the value that will be returned, or None if the event is caused by an exception being raised. The trace function's return value is ignored.

'exception'

An exception has occurred. The local trace function is called; arg is a tuple (exception, value, traceback); the return value specifies the new local trace function.

'opcode'

The interpreter is about to execute a new opcode (see dis for opcode details). The local trace function is called; arg is None; the return value specifies the new local trace function. Per-opcode events are not emitted by default: they must be explicitly requested by setting f_trace_opcodes to True on the frame.

Note that as an exception is propagated down the chain of callers, an 'exception' event is generated at each level.

For more fine-grained usage, it's possible to set a trace function by assigning frame.f_trace = tracefunc explicitly, rather than relying on it being set indirectly via the return value from an already installed trace function. This is also required for activating the trace function on the current frame, which settrace() doesn't do. Note that in order for this to work, a global tracing function must have been installed with settrace() in order to enable the runtime tracing machinery, but it doesn't need to be the same tracing function (e.g. it could be a low overhead tracing function that simply returns None to disable itself immediately on each frame).

For more information on code and frame objects, refer to 標準型別階層.

引發一個不附帶引數的稽核事件 sys.settrace。

CPython 實作細節： The settrace() function is intended only for implementing debuggers, profilers, coverage tools and the like. Its behavior is part of the implementation platform, rather than part of the language definition, and thus may not be available in all Python implementations.

在 3.7 版的變更: 'opcode' event type added; f_trace_lines and f_trace_opcodes attributes added to frames

sys.set_asyncgen_hooks([firstiter] [, finalizer])

Accepts two optional keyword arguments which are callables that accept an asynchronous generator iterator as an argument. The firstiter callable will be called when an asynchronous generator is iterated for the first time. The finalizer will be called when an asynchronous generator is about to be garbage collected.

引發一個不附帶引數的稽核事件 sys.set_asyncgen_hooks_firstiter。

引發一個不附帶引數的稽核事件 sys.set_asyncgen_hooks_finalizer。

Two auditing events are raised because the underlying API consists of two calls, each of which must raise its own event.

在 3.6 版被加入: See PEP 525 for more details, and for a reference example of a finalizer method see the implementation of asyncio.Loop.shutdown_asyncgens in Lib/asyncio/base_events.py

備註

This function has been added on a provisional basis (see PEP 411 for details.)

sys.set_coroutine_origin_tracking_depth(depth)

Allows enabling or disabling coroutine origin tracking. When enabled, the cr_origin attribute on coroutine objects will contain a tuple of (filename, line number, function name) tuples describing the traceback where the coroutine object was created, with the most recent call first. When disabled, cr_origin will be None.

To enable, pass a depth value greater than zero; this sets the number of frames whose information will be captured. To disable, set depth to zero.

This setting is thread-specific.

在 3.7 版被加入.

備註

This function has been added on a provisional basis (see PEP 411 for details.) Use it only for debugging purposes.

sys.activate_stack_trampoline(backend, /)

Activate the stack profiler trampoline backend. The only supported backend is "perf".

Stack trampolines cannot be activated if the JIT is active.

可用性: Linux.

在 3.12 版被加入.

也參考

• Python 對 Linux perf 分析器的支援

• https://perf.wiki.kernel.org

sys.deactivate_stack_trampoline()

Deactivate the current stack profiler trampoline backend.

If no stack profiler is activated, this function has no effect.

可用性: Linux.

在 3.12 版被加入.

sys.is_stack_trampoline_active()

Return True if a stack profiler trampoline is active.

可用性: Linux.

在 3.12 版被加入.

sys.remote_exec(pid, script)

Executes script, a file containing Python code in the remote process with the given pid.

This function returns immediately, and the code will be executed by the target process's main thread at the next available opportunity, similarly to how signals are handled. There is no interface to determine when the code has been executed. The caller is responsible for making sure that the file still exists whenever the remote process tries to read it and that it hasn't been overwritten.

The remote process must be running a CPython interpreter of the same major and minor version as the local process. If either the local or remote interpreter is pre-release (alpha, beta, or release candidate) then the local and remote interpreters must be the same exact version.

When the code is executed in the remote process, an auditing event sys.remote_exec is raised with the pid and the path to the script file. This event is raised in the process that called sys.remote_exec().

When the script is executed in the remote process, an auditing event cpython.remote_debugger_script is raised with the path in the remote process. This event is raised in the remote process, not the one that called sys.remote_exec().

可用性: Unix, Windows.

在 3.14 版被加入.

sys._enablelegacywindowsfsencoding()

Changes the filesystem encoding and error handler to 'mbcs' and 'replace' respectively, for consistency with versions of Python prior to 3.6.

This is equivalent to defining the PYTHONLEGACYWINDOWSFSENCODING environment variable before launching Python.

See also sys.getfilesystemencoding() and sys.getfilesystemencodeerrors().

可用性: Windows.

備註

Changing the filesystem encoding after Python startup is risky because the old fsencoding or paths encoded by the old fsencoding may be cached somewhere. Use PYTHONLEGACYWINDOWSFSENCODING instead.

在 3.6 版被加入: 更多細節請見 PEP 529。

Deprecated since version 3.13, will be removed in version 3.16: Use PYTHONLEGACYWINDOWSFSENCODING instead.

sys.stdin

sys.stdout

sys.stderr

File objects used by the interpreter for standard input, output and errors:

• stdin is used for all interactive input (including calls to input());

• stdout is used for the output of print() and expression statements and for the prompts of input();

• The interpreter's own prompts and its error messages go to stderr.

These streams are regular text files like those returned by the open() function. Their parameters are chosen as follows:

• The encoding and error handling are is initialized from PyConfig.stdio_encoding and PyConfig.stdio_errors.

  On Windows, UTF-8 is used for the console device. Non-character devices such as disk files and pipes use the system locale encoding (i.e. the ANSI codepage). Non-console character devices such as NUL (i.e. where isatty() returns True) use the value of the console input and output codepages at startup, respectively for stdin and stdout/stderr. This defaults to the system locale encoding if the process is not initially attached to a console.

  The special behaviour of the console can be overridden by setting the environment variable PYTHONLEGACYWINDOWSSTDIO before starting Python. In that case, the console codepages are used as for any other character device.

  Under all platforms, you can override the character encoding by setting the PYTHONIOENCODING environment variable before starting Python or by using the new -X utf8 command line option and PYTHONUTF8 environment variable. However, for the Windows console, this only applies when PYTHONLEGACYWINDOWSSTDIO is also set.

• When interactive, the stdout stream is line-buffered. Otherwise, it is block-buffered like regular text files. The stderr stream is line-buffered in both cases. You can make both streams unbuffered by passing the -u command-line option or setting the PYTHONUNBUFFERED environment variable.

在 3.9 版的變更: Non-interactive stderr is now line-buffered instead of fully buffered.

備註

To write or read binary data from/to the standard streams, use the underlying binary buffer object. For example, to write bytes to stdout, use sys.stdout.buffer.write(b'abc').

However, if you are writing a library (and do not control in which context its code will be executed), be aware that the standard streams may be replaced with file-like objects like io.StringIO which do not support the buffer attribute.

sys.__stdin__

sys.__stdout__

sys.__stderr__

These objects contain the original values of stdin, stderr and stdout at the start of the program. They are used during finalization, and could be useful to print to the actual standard stream no matter if the sys.std* object has been redirected.

It can also be used to restore the actual files to known working file objects in case they have been overwritten with a broken object. However, the preferred way to do this is to explicitly save the previous stream before replacing it, and restore the saved object.

備註

Under some conditions stdin, stdout and stderr as well as the original values __stdin__, __stdout__ and __stderr__ can be None. It is usually the case for Windows GUI apps that aren't connected to a console and Python apps started with pythonw.

sys.stdlib_module_names

A frozenset of strings containing the names of standard library modules.

It is the same on all platforms. Modules which are not available on some platforms and modules disabled at Python build are also listed. All module kinds are listed: pure Python, built-in, frozen and extension modules. Test modules are excluded.

For packages, only the main package is listed: sub-packages and sub-modules are not listed. For example, the email package is listed, but the email.mime sub-package and the email.message sub-module are not listed.

另請參閱 sys.builtin_module_names 清單。

在 3.10 版被加入.

sys.thread_info

A named tuple holding information about the thread implementation.

thread_info.name

The name of the thread implementation:

• "nt": Windows 執行緒

• "pthread": POSIX 執行緒

• "pthread-stubs": stub POSIX threads (on WebAssembly platforms without threading support)

• "solaris": Solaris threads

thread_info.lock

The name of the lock implementation:

• "semaphore": a lock uses a semaphore

• "mutex+cond": a lock uses a mutex and a condition variable

• 為 None 表示此資訊未知

thread_info.version

The name and version of the thread library. It is a string, or None if this information is unknown.

在 3.3 版被加入.

sys.tracebacklimit

When this variable is set to an integer value, it determines the maximum number of levels of traceback information printed when an unhandled exception occurs. The default is 1000. When set to 0 or less, all traceback information is suppressed and only the exception type and value are printed.

sys.unraisablehook(unraisable, /)

處理一個不可被引發的例外。

Called when an exception has occurred but there is no way for Python to handle it. For example, when a destructor raises an exception or during garbage collection (gc.collect()).

unraisable 引數具有以下屬性：

• exc_type: 例外型別。

• exc_value: 例外值，可以為 None。

• exc_traceback: 例外追蹤，可以為 None。

• err_msg: 錯誤訊息，可以為 None。

• object: 導致例外的物件，可以為 None。

The default hook formats err_msg and object as: f'{err_msg}: {object!r}'; use "Exception ignored in" error message if err_msg is None.

sys.unraisablehook() can be overridden to control how unraisable exceptions are handled.

也參考

處理未被捕捉到例外的 excepthook()。

警告

Storing exc_value using a custom hook can create a reference cycle. It should be cleared explicitly to break the reference cycle when the exception is no longer needed.

Storing object using a custom hook can resurrect it if it is set to an object which is being finalized. Avoid storing object after the custom hook completes to avoid resurrecting objects.

Raise an auditing event sys.unraisablehook with arguments hook, unraisable when an exception that cannot be handled occurs. The unraisable object is the same as what will be passed to the hook. If no hook has been set, hook may be None.

在 3.8 版被加入.

sys.version

A string containing the version number of the Python interpreter plus additional information on the build number and compiler used. This string is displayed when the interactive interpreter is started. Do not extract version information out of it, rather, use version_info and the functions provided by the platform module.

sys.api_version

The C API version, equivalent to the C macro PYTHON_API_VERSION. Defined for backwards compatibility.

Currently, this constant is not updated in new Python versions, and is not useful for versioning. This may change in the future.

sys.version_info

A tuple containing the five components of the version number: major, minor, micro, releaselevel, and serial. All values except releaselevel are integers; the release level is 'alpha', 'beta', 'candidate', or 'final'. The version_info value corresponding to the Python version 2.0 is (2, 0, 0, 'final', 0). The components can also be accessed by name, so sys.version_info[0] is equivalent to sys.version_info.major and so on.

在 3.1 版的變更: 新增了附名的元件屬性。

sys.warnoptions

This is an implementation detail of the warnings framework; do not modify this value. Refer to the warnings module for more information on the warnings framework.

sys.winver

The version number used to form registry keys on Windows platforms. This is stored as string resource 1000 in the Python DLL. The value is normally the major and minor versions of the running Python interpreter. It is provided in the sys module for informational purposes; modifying this value has no effect on the registry keys used by Python.

可用性: Windows.

sys.monitoring

Namespace containing functions and constants for register callbacks and controlling monitoring events. See sys.monitoring for details.

sys._xoptions

A dictionary of the various implementation-specific flags passed through the -X command-line option. Option names are either mapped to their values, if given explicitly, or to True. Example:

$ ./python -Xa=b -Xc
Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys._xoptions
{'a': 'b', 'c': True}

CPython 實作細節： This is a CPython-specific way of accessing options passed through -X. Other implementations may export them through other means, or not at all.

在 3.2 版被加入.

引用

[C99]

ISO/IEC 9899:1999. "Programming languages -- C." 公開草案可在以下網址取得 https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf。