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.
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).
適用: Unix.
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.
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].
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.
Set during Python startup, before site.py is run, to the same value as
exec_prefix. If not running in a
virtual environment, the values will stay the same; if
site.py finds that a virtual environment is in use, the values of
prefix and exec_prefix will be changed to point to the
virtual environment, whereas base_prefix and
base_exec_prefix will remain pointing to the base Python
installation (the one which the virtual environment was created from).
在 3.3 版被加入.
Set during Python startup, before site.py is run, to the same value as
prefix. If not running in a virtual environment, the values
will stay the same; if site.py finds that a virtual environment is in
use, the values of prefix and exec_prefix will be changed to
point to the virtual environment, whereas base_prefix and
base_exec_prefix will remain pointing to the base Python
installation (the one which the virtual environment was created from).
在 3.3 版被加入.
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.
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。
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.
A string containing the copyright pertaining to the Python interpreter.
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.
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.
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。
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().
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.
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.
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.
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.
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 version as tuple of ints (major, minor, micro), e.g. (3, 1, 8).
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'。
True if Python is compiled with Emscripten pthreads support.
True if Python is compiled with shared memory support.
適用: Emscripten.
在 3.11 版被加入.
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.
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().
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__
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.
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().
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
value will be changed in site.py to point to the virtual environment.
The value for the Python installation will still be available, via
base_exec_prefix.
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.
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.
The named tuple flags exposes the status of command line flags. The attributes are read only.
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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。
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.
屬性 |
float.h macro |
解釋 |
|---|---|---|
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difference between 1.0 and the least value greater than 1.0 that is representable as a float. 另請參閱 |
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The maximum number of decimal digits that can be faithfully represented in a float; see below. |
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Float precision: the number of base- |
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The maximum representable positive finite float. |
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The maximum integer e such that |
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The maximum integer e such that |
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The minimum representable positive normalized float. Use |
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The minimum integer e such that |
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The minimum integer e such that |
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The radix of exponent representation. |
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An integer representing the rounding mode for floating-point arithmetic.
This reflects the value of the system
All other values for |
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'
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.
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.
Return the number of unicode objects that have been interned.
在 3.12 版被加入.
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().
適用: Android.
在 3.7 版被加入.
Return 'utf-8'. This is the name of the default string encoding, used
in methods like str.encode().
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).
適用: Unix.
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.
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.
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.
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.
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.
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().
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.
Return the interpreter's "thread switch interval" in seconds; see
setswitchinterval().
在 3.2 版被加入.
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.
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.
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 3.13.1 版的變更: The result may include objects from other interpreters.
Get the profiler function as set by setprofile().
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.
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 |
|---|---|
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The system is a workstation. |
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The system is a domain controller. |
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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.
適用: 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
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.)
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.
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.
The width in bits used for hash values
The prime modulus P used for numeric hash scheme
The hash value returned for a positive infinity
(This attribute is no longer used)
The multiplier used for the imaginary part of a complex number
The name of the algorithm for hashing of str, bytes, and memoryview
The internal output size of the hash algorithm
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
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.
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.
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.
備註
The addition of new required attributes must go through the normal PEP process. See PEP 421 for more information.
A named tuple that holds information about Python's internal representation of integers. The attributes are read only.
The number of bits held in each digit.
Python integers are stored internally in base 2**int_info.bits_per_digit.
The size in bytes of the C type used to represent a digit.
The default value for sys.get_int_max_str_digits()
when it is not otherwise explicitly configured.
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。
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.
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.
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.
Return True if the main Python interpreter is
shutting down. Return False otherwise.
See also the PythonFinalizationError exception.
在 3.5 版被加入.
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.
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.
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.
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.
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.
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.MetaPathFinderThe abstract base class defining the interface of finder objects on
meta_path.
importlib.machinery.ModuleSpecThe 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.
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.
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.
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.
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.
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.
A string containing a platform identifier. Known values are:
System |
|
|---|---|
AIX |
|
Android |
|
Emscripten |
|
iOS |
|
Linux |
|
macOS |
|
Windows |
|
Windows/Cygwin |
|
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' or 'freebsd8', 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('freebsd'):
# FreeBSD-specific code here...
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'.
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.
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.
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
value will be changed in site.py to point to the virtual
environment. The value for the Python installation will still be
available, via base_prefix.
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.
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).
適用: Unix.
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.
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。
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.
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.
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
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.)
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, pass 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.
Activate the stack profiler trampoline backend.
The only supported backend is "perf".
適用: Linux.
在 3.12 版被加入.
Deactivate the current stack profiler trampoline backend.
If no stack profiler is activated, this function has no effect.
適用: Linux.
在 3.12 版被加入.
Return True if a stack profiler trampoline is active.
適用: Linux.
在 3.12 版被加入.
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().
適用: 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.
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.
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.
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.
A named tuple holding information about the thread implementation.
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
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
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.
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.
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()).
The unraisable argument has the following attributes:
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.
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.
The C API version for this interpreter. Programmers may find this useful when debugging version conflicts between Python and extension modules.
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。
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.
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.
適用: Windows.
Namespace containing functions and constants for register callbacks
and controlling monitoring events.
See sys.monitoring for details.
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
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。