sys
— 特定系统参数和函数
¶
此模块提供对由解释器使用或维护的一些变量的访问，及对与解释器强交互函数的访问。它始终可用。
sys.
argv
¶
传递给 Python 脚本的命令行自变量列表。
argv[0]
是脚本名称 (它是否为完整路径名从属操作系统)。若命令的执行是使用
-c
命令行选项到解释器，
argv[0]
被设为字符串
'-c'
。若脚本名称未被传递给 Python 解释器，
argv[0]
是空字符串。
要循环标准输入或命令行中给出的文件列表，见
fileinput
模块。
sys.
base_exec_prefix
¶
Set during Python startup, before
site.py
is run, to the same value as
exec_prefix
。若未运行在
虚拟环境
, 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).
3.3 版新增。
sys.
base_prefix
¶
Set during Python startup, before
site.py
is run, to the same value as
prefix
。若未运行在
虚拟环境
, 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).
3.3 版新增。
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 giving 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.)
sys.
call_tracing
(
func
,
args
)
¶
调用
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 some other code.
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.
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.
sys.
_debugmallocstats
(
)
¶
Print low-level information to stderr about the state of CPython’s memory allocator.
If Python is configured –with-pydebug, it also performs some expensive internal consistency checks.
3.3 版新增。
CPython 实现细节： 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. Availability: Windows.
sys.
displayhook
(
value
)
¶
若
value
不是
None
，此函数打印
repr(value)
to
sys.stdout
，并保存
value
in
builtins._
。若
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'
错误处理程序。
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
.
伪代码：
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
3.2 版改变：
使用
'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.
excepthook
(
type
,
value
,
traceback
)
¶
该函数把给定回溯和异常输出到
sys.stderr
.
When an exception 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
.
sys.
__displayhook__
¶
sys.
__excepthook__
¶
这些对象包含原始值的
displayhook
and
excepthook
at the start of the program. They are saved so that
displayhook
and
excepthook
can be restored in case they happen to get replaced with broken objects.
sys.
exc_info
(
)
¶
此函数返回给出目前正处理异常有关信息的 3 值元组。返回信息特定于当前线程和当前堆栈帧。若当前堆栈帧未处理异常，则从调用堆栈帧或其调用者处获取信息，依此类推，直到找到正处理异常的堆栈帧。此处，处理异常被定义为执行 except 子句。对于任何堆栈帧，只可访问目前正处理异常的有关信息。
若在堆栈的任何地方都没有要处理的异常，则元组包含 3
None
值被返回。否则，返回值是
(type,
value,
traceback)
。它们的含义：
type
获取正处理异常的类型 (子类化的
BaseException
);
value
获取异常实例 (异常类型实例)；
traceback
获取回溯对象 (见参考手册) 封装最初发生异常点的调用堆栈。
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/python
X.Y
/config
, and shared library modules are installed in
exec_prefix
/lib/python
X.Y
/lib-dynload
，其中
X.Y
is the version number of Python, for example
3.2
.
注意
若
虚拟环境
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
.
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
将是空字符串或
None
.
sys.
exit
(
[
arg
]
)
¶
退出从 Python。这被实现通过引发
SystemExit
异常，因此清理动作的指定通过 finally 子句的
try
语句的承兑，且在外层拦截退出尝试是可能的。
可选自变量
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.
3.6 版改变：
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
¶
结构序列 flags exposes the status of command line flags. The attributes are read only.
| 属性 | flag |
|---|---|
debug
|
-d
|
inspect
|
-i
|
interactive
|
-i
|
isolated
|
-I
|
optimize
|
-O
or
-OO
|
dont_write_bytecode
|
-B
|
no_user_site
|
-s
|
no_site
|
-S
|
ignore_environment
|
-E
|
verbose
|
-v
|
bytes_warning
|
-b
|
quiet
|
-q
|
hash_randomization
|
-R
|
3.2 版改变：
添加
quiet
属性为新
-q
标志。
3.2.3 版新增：
hash_randomization
属性。
3.3 版改变：
移除过时
division_warning
属性。
3.4 版改变：
添加
isolated
属性为
-I
isolated
标志。
sys.
float_info
¶
结构序列
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.
| 属性 | float.h 宏 | 解释 |
|---|---|---|
epsilon
|
DBL_EPSILON | difference between 1 and the least value greater than 1 that is representable as a float |
dig
|
DBL_DIG | maximum number of decimal digits that can be faithfully represented in a float; see below |
mant_dig
|
DBL_MANT_DIG |
float precision: the number of base-
radix
digits in the significand of a float
|
max
|
DBL_MAX | maximum representable finite float |
max_exp
|
DBL_MAX_EXP |
maximum integer e such that
radix**(e-1)
is a representable finite float
|
max_10_exp
|
DBL_MAX_10_EXP |
maximum integer e such that
10**e
is in the range of representable finite floats
|
min
|
DBL_MIN | 最小正规范化浮点 |
min_exp
|
DBL_MIN_EXP |
minimum integer e such that
radix**(e-1)
is a normalized float
|
min_10_exp
|
DBL_MIN_10_EXP |
minimum integer e such that
10**e
is a normalized float
|
radix
|
FLT_RADIX | 表示指数的基数 |
rounds
|
FLT_ROUNDS | integer constant representing the rounding mode used for arithmetic operations. This reflects the value of the system FLT_ROUNDS macro at interpreter startup time. See section 5.2.4.2.2 of the C99 standard for an explanation of the possible values and their meanings. |
属性
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.
3.1 版新增。
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_type_cache()
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.
3.4 版新增。
sys.
getcheckinterval
(
)
¶
返回解释器的校验间隔；见
setcheckinterval()
.
从 3.2 版起弃用：
使用
getswitchinterval()
代替。
sys.
getdefaultencoding
(
)
¶
Return the name of the current default string encoding used by the Unicode implementation.
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
模块 (
RTLD_xxx
constants, e.g.
os.RTLD_LAZY
). Availability: Unix.
sys.
getfilesystemencoding
(
)
¶
Return the name of the encoding used to convert between Unicode filenames and bytes filenames. 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.
此编码始终兼容 ASCII。
os.fsencode()
and
os.fsdecode()
should be used to ensure that the correct encoding and errors mode are used.
'utf-8'
.
'utf-8'
or
'mbcs'
，从属用户配置。
3.2 版改变：
getfilesystemencoding()
结果不可以是
None
不再。
3.6 版改变：
Windows is no longer guaranteed to return
'mbcs'
。见
PEP 529
and
_enablelegacywindowsfsencoding()
了解更多信息。
sys.
getfilesystemencodeerrors
(
)
¶
Return the name of the error mode used to convert between Unicode filenames and bytes filenames. The encoding name is returned from
getfilesystemencoding()
.
os.fsencode()
and
os.fsdecode()
should be used to ensure that the correct encoding and errors mode are used.
3.6 版新增。
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()
.
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.
若给定，
default
will be returned if the object does not provide means to retrieve the size. Otherwise a
TypeError
会被引发。
getsizeof()
calls the object’s
__sizeof__
method and adds an additional garbage collector overhead if the object is managed by the garbage collector.
见
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”; see
setswitchinterval()
.
3.2 版新增。
sys.
_getframe
(
[
depth
]
)
¶
从调用堆栈返回帧对象。若可选整数
depth
有给定，返回堆栈顶部下方许多调用帧对象。若比调用堆栈更深，
ValueError
被引发。默认
depth
为 0，返回调用堆栈顶部帧。
CPython 实现细节： 此函数只应用于内部和专用目的。它不保证在所有 Python 实现中均存在。
sys.
getprofile
(
)
¶
Get the profiler function as set by
setprofile()
.
sys.
gettrace
(
)
¶
Get the trace function as set by
settrace()
.
CPython 实现细节：
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]
相当于
sys.getwindowsversion().major
. For compatibility with prior versions, only the first 5 elements are retrievable by indexing.
platform
将是
2
(VER_PLATFORM_WIN32_NT)
.
product_type may be one of the following values:
| 常量 | 含义 |
|---|---|
1
(VER_NT_WORKSTATION)
|
系统是工作站。 |
2
(VER_NT_DOMAIN_CONTROLLER)
|
系统是域控制器。 |
3
(VER_NT_SERVER)
|
系统是服务器，但不是域控制器。 |
此函数包裹 Win32
GetVersionEx()
function; see the Microsoft documentation on
OSVERSIONINFOEX()
for more information about these fields.
platform_version returns the accurate 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.
可用性：Windows。
3.2 版改变： Changed to a named tuple and added service_pack_minor , service_pack_major , suite_mask ，和 product_type .
3.6 版改变： 添加 platform_version
sys.
get_asyncgen_hooks
(
)
¶
返回
asyncgen_hooks
object, which is similar to a
namedtuple
of the form
(firstiter, finalizer)
，其中
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 asychronous generator by an event loop.
3.6 版新增： 见 PEP 525 了解更多细节。
注意
此函数已被添加在暂行基础上 (见 PEP 411 了解细节。)
sys.
get_coroutine_wrapper
(
)
¶
返回
None
, or a wrapper set by
set_coroutine_wrapper()
.
3.5 版新增： 见 PEP 492 了解更多细节。
注意
此函数已被添加在暂行基础上 (见 PEP 411 for details.) Use it only for debugging purposes.
sys.
hash_info
¶
结构序列 giving parameters of the numeric hash implementation. For more details about hashing of numeric types, see 数值类型的哈希 .
| 属性 | 解释 |
|---|---|
width
|
width in bits used for hash values |
modulus
|
prime modulus P used for numeric hash scheme |
inf
|
hash value returned for a positive infinity |
nan
|
hash value returned for a nan |
imag
|
multiplier used for the imaginary part of a complex number |
algorithm
|
name of the algorithm for hashing of str, bytes, and memoryview |
hash_bits
|
internal output size of the hash algorithm |
seed_bits
|
size of the seed key of the hash algorithm |
3.2 版新增。
3.4 版改变： 添加 algorithm , hash_bits and 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
结构序列
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 版本控制
.
sys.
实现
¶
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
实现
. 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)
，而
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
被设为
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
了解更多信息。
3.3 版新增。
sys.
int_info
¶
结构序列 that holds information about Python’s internal representation of integers. The attributes are read only.
| 属性 | 解释 |
|---|---|
bits_per_digit
|
number of bits held in each digit. Python integers are stored internally in base
2**int_info.bits_per_digit
|
sizeof_digit
|
size in bytes of the C type used to represent a digit |
3.1 版新增。
sys.
__interactivehook__
¶
When this attribute exists, its value is automatically called (with no arguments) when the interpreter is launched in
交互模式
. This is done after the
PYTHONSTARTUP
file is read, so that you can set this hook there. The
site
模块
sets this
.
3.4 版新增。
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_finalizing
(
)
¶
返回
True
若 Python 解释器是
shutting down
,
False
否则。
3.5 版新增。
sys.
last_type
¶
sys.
last_value
¶
sys.
last_traceback
¶
These three variables are not always defined; they are set when an exception is not handled and the interpreter prints an error message and a stack traceback. Their 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.)
The meaning of the variables is the same as that of the return values 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).
3.3 版改变：
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. 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
，或
None
if the module cannot be found.
另请参阅
importlib.abc.MetaPathFinder
meta_path
.
importlib.machinery.ModuleSpec
find_spec()
应返回实例。
3.4 版改变：
Module specs
were introduced in Python 3.4, by
PEP 451
. Earlier versions of Python looked for a method called
find_module()
. This is still called as a fallback if a
meta_path
entry doesn’t have a
find_spec()
方法。
sys.
模块
¶
这是将模块名称映射到已加载模块的字典。这可以被操纵以强制重新加载模块及其它技巧。不管怎样，替换字典必然不按预期工作，且从字典删除必需项可能导致 Python 失败。
sys.
path
¶
A list of strings that specifies the search path for modules. Initialized from the environment variable
PYTHONPATH
, plus an installation-dependent default.
As initialized upon program startup, the first item of this list,
path[0]
, is the directory containing the script that was used to invoke the Python interpreter. If the script directory is not available (e.g. if the interpreter is invoked interactively or if the script is read from standard input),
path[0]
is the empty string, which directs Python to search modules in the current directory first. Notice that the script directory is inserted
before
the entries inserted as a result of
PYTHONPATH
.
A program is free to modify this list for its own purposes. Only strings and bytes should be added to
sys.path
; all other data types are ignored during import.
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
.
最初的指定在 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
是存储。
最初的指定在 PEP 302 .
3.3 版改变：
None
is stored instead of
imp.NullImporter
when no finder is found.
sys.
platform
¶
This string contains a platform identifier that can be used to append platform-specific components to
sys.path
，例如。
For Unix systems, except on Linux, this 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...
elif sys.platform.startswith('linux'):
# Linux-specific code here...
对于其它系统，值是：
| 系统 |
platform
value
|
|---|---|
| Linux |
'linux'
|
| Windows |
'win32'
|
| Windows/Cygwin |
'cygwin'
|
| Mac OS X |
'darwin'
|
3.3 版改变：
在 Linux，
sys.platform
不再包含主要版本。它始终是
'linux'
，而不是
'linux2'
or
'linux3'
. Since older Python versions include the version number, it is recommended to always use the
startswith
idiom presented above.
sys.
prefix
¶
A string giving the site-specific directory prefix where the platform independent Python files are installed; by default, this is the string
'/usr/local'
. This can be set at build time with the
--prefix
argument to the
configure
script. The main collection of Python library modules is installed in the directory
prefix
/lib/python
X.Y
while the platform independent header files (all except
pyconfig.h
) are stored in
prefix
/include/python
X.Y
，其中
X.Y
is the version number of Python, for example
3.2
.
注意
若
虚拟环境
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
.
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.
setcheckinterval
(
interval
)
¶
Set the interpreter’s “check interval”. This integer value determines how often the interpreter checks for periodic things such as thread switches and signal handlers. The default is
100
, meaning the check is performed every 100 Python virtual instructions. Setting it to a larger value may increase performance for programs using threads. Setting it to a value
<=
0 checks every virtual instruction, maximizing responsiveness as well as overhead.
从 3.2 版起弃用：
This function doesn’t have an effect anymore, as the internal logic for thread switching and asynchronous tasks has been rewritten. Use
setswitchinterval()
代替。
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
模块 (
RTLD_xxx
constants, e.g.
os.RTLD_LAZY
).
可用性：Unix。
sys.
setprofile
(
profilefunc
)
¶
Set the system’s profile function, which allows you to implement a Python source code profiler in Python. See chapter
The Python Profilers
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
.
Profile functions should have three arguments:
frame
,
event
，和
arg
.
frame
is the current stack frame.
event
is a string:
'call'
,
'return'
,
'c_call'
,
'c_return'
，或
'c_exception'
.
arg
depends on the event type.
事件拥有下列含义：
'call'
None
.
'return'
None
if the event is caused by an exception being raised.
'c_call'
'c_return'
'c_exception'
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
异常被引发。
3.5.1 版改变：
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.
3.2 版新增。
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 be registered using
settrace()
for each thread being debugged.
Trace functions should have three arguments:
frame
,
event
，和
arg
.
frame
is the current stack frame.
event
is a string:
'call'
,
'line'
,
'return'
or
'exception'
.
arg
depends on the event type.
The trace function is invoked (with
event
设为
'call'
) whenever a new local scope is entered; it should return a reference to a local trace function to be used that scope, or
None
if the scope shouldn’t be traced.
The local trace function should return a reference to itself (or to another function for further tracing in that scope), or
None
to turn off tracing in that scope.
事件拥有下列含义：
'call'
None
; the return value specifies the local trace function.
'line'
None
; the return value specifies the new local trace function. See
Objects/lnotab_notes.txt
for a detailed explanation of how this works.
'return'
None
if the event is caused by an exception being raised. The trace function’s return value is ignored.
'exception'
(exception,
value,
traceback)
; the return value specifies the new local trace function.
Note that as an exception is propagated down the chain of callers, an
'exception'
event is generated at each level.
For more information on code and frame objects, refer to 标准类型层次结构 .
CPython 实现细节：
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.
sys.
set_asyncgen_hooks
(
firstiter
,
finalizer
)
¶
Accepts two optional keyword arguments which are callables that accept an asynchronous generator iterator 作为自变量。 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.
3.6 版新增：
见
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
注意
此函数已被添加在暂行基础上 (见 PEP 411 了解细节。)
sys.
set_coroutine_wrapper
(
wrapper
)
¶
允许拦截创建的
协程
objects (only ones that are created by an
async
def
function; generators decorated with
types.coroutine()
or
asyncio.coroutine()
will not be intercepted).
wrapper 自变量必须是：
None
, to reset the wrapper.
If called twice, the new wrapper replaces the previous one. The function is thread-specific.
wrapper callable cannot define new coroutines directly or indirectly:
def wrapper(coro):
async def wrap(coro):
return await coro
return wrap(coro)
sys.set_coroutine_wrapper(wrapper)
async def foo():
pass
# The following line will fail with a RuntimeError, because
# ``wrapper`` creates a ``wrap(coro)`` coroutine:
foo()
另请参阅
get_coroutine_wrapper()
.
3.5 版新增： 见 PEP 492 了解更多细节。
注意
此函数已被添加在暂行基础上 (见 PEP 411 for details.) Use it only for debugging purposes.
sys.
_enablelegacywindowsfsencoding
(
)
¶
Changes the default filesystem encoding and errors mode to ‘mbcs’ and ‘replace’ respectively, for consistency with versions of Python prior to 3.6.
这相当于定义
PYTHONLEGACYWINDOWSFSENCODING
环境变量在启动 Python 之前。
可用性：Windows
3.6 版新增： 见 PEP 529 了解更多细节。
sys.
stdin
¶
sys.
stdout
¶
sys.
stderr
¶
文件对象 用于解释器为标准输入、标准输出及标准错误：
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()
;
stderr
.
这些流是常规
文本文件
like those returned by the
open()
function. Their parameters are chosen as follows:
The character encoding is platform-dependent. Under Windows, if the stream is interactive (that is, if its
isatty()
方法返回
True
), the console codepage is used, otherwise the ANSI code page. Under other platforms, the locale encoding is used (see
locale.getpreferredencoding()
).
Under all platforms though, you can override this value by setting the
PYTHONIOENCODING
environment variable before starting Python.
When interactive, standard streams are line-buffered. Otherwise, they are block-buffered like regular text files. You can override this value with the
-u
command-line option.
注意
要写入 (或读取) 二进制数据从/到标准流，使用底层二进制
buffer
对象。例如：要写入 bytes 到
stdout
，使用
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
属性。
sys.
__stdin__
¶
sys.
__stdout__
¶
sys.
__stderr__
¶
这些对象包含原始值的
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.
注意
Under some conditions
stdin
,
stdout
and
stderr
as well as the original values
__stdin__
,
__stdout__
and
__stderr__
可以是
None
. It is usually the case for Windows GUI apps that aren’t connected to a console and Python apps started with
pythonw
.
sys.
thread_info
¶
结构序列 保持线程实现的有关信息。
| 属性 | 解释 |
|---|---|
name
|
线程实现的名称：
|
lock
|
锁实现的名称：
|
version
|
Name and version of the thread library. It is a string, or
None
if these informations are unknown.
|
3.3 版新增。
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.
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
模块。
sys.
api_version
¶
The C API version for this interpreter. Programmers may find this useful when debugging version conflicts between Python and extension modules.
sys.
version_info
¶
A tuple containing the five components of the version number:
major
,
minor
,
micro
,
releaselevel
，和
serial
. All values except
releaselevel
are integers; the release level is
'alpha'
,
'beta'
,
'candidate'
，或
'final'
。
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]
相当于
sys.version_info.major
and so on.
3.1 版改变： 添加命名组件属性。
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 first three characters of
version
. It is provided in the
sys
module for informational purposes; modifying this value has no effect on the registry keys used by Python. Availability: Windows.
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
。范例：
$ ./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 实现细节：
This is a CPython-specific way of accessing options passed through
-X
. Other implementations may export them through other means, or not at all.
3.2 版新增。
引文
| [C99] | ISO/IEC 9899:1999. “Programming languages – C.” A public draft of this standard is available at http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf . |