28.1. 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. 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.

2.0 版新增。

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() 只列表导入模块)。

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 ¶

包含 Python 解释器版权归属的字符串。

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.

此功能只应用于内部和专用目的。

2.6 版新增。

sys. _current_frames ( ) ¶

返回将每个线程的标识符，映射到在该线程中目前处于活动状态 (当调用函数时) 的最顶层堆栈帧的字典。注意，该函数在 traceback 模块可以构建给出这样的帧的调用堆栈。

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.

此功能只应用于内部和专用目的。

2.5 版新增。

sys. dllhandle ¶

Integer specifying the handle of the Python DLL. Availability: Windows.

sys. displayhook ( 值 ) ¶

若 value 不是 None , this function prints it to sys.stdout , and saves it in __builtin__._ .

sys.displayhook 被调用当为结果估算 表达式 进入交互 Python 会话。可以定制这些值的显示，通过将另一 1 自变量函数赋值给 sys.displayhook .

sys. dont_write_bytecode ¶

若这为 True，Python 不会试着写入 .pyc or .pyo 文件当导入源模块时。此值最初被设为 True or False 从属 -B 命令行选项和 PYTHONDONTWRITEBYTECODE 环境变量，但自己可以设置它以控制字节码文件的生成。

2.6 版新增。

sys. excepthook ( type , 值 , traceback ) ¶

此函数将给定回溯和异常输出到 sys.stderr .

当异常被引发且未捕获时，解释器调用 sys.excepthook 采用异常类、异常实例和回溯对象 3 自变量。在交互会话中，这恰好发生在控制返回给提示之前；在 Python 程序中，这恰好发生在程序退出之前。这种顶层异常的处理可以定制，通过赋值另一 3 自变量函数给 sys.excepthook .

sys. __displayhook__ ¶

sys. __excepthook__ ¶

这些对象包含原始值的 displayhook and excepthook 在程序启动时。保存它们以便 displayhook and excepthook can be restored in case they happen to get replaced with broken objects.

sys. exc_info ( ) ¶

This function returns a tuple of three values that give information about the exception that is currently being handled. The information returned is specific both to the current thread and to the current stack frame. If the current stack frame is not handling an exception, the information is taken from the calling stack frame, or its caller, and so on until a stack frame is found that is handling an exception. Here, “handling an exception” is defined as “executing or having executed an except clause.” For any stack frame, only information about the most recently handled exception is accessible.

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 gets the exception type of the exception being handled (a class object); value gets the exception parameter (its associated value or the second argument to raise , which is always a class instance if the exception type is a class object); 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。

若 exc_clear() is called, this function will return three None values until either another exception is raised in the current thread or the execution stack returns to a frame where another exception is being handled.

警告

Assigning the traceback return value to a local variable in a function that is handling an exception will cause a circular reference. This will prevent anything referenced by a local variable in the same function or by the traceback from being garbage collected. Since most functions don’t need access to the traceback, the best solution is to use something like exctype, value = sys.exc_info()[:2] to extract only the exception type and value. If you do need the traceback, make sure to delete it after use (best done with a try … finally statement) or to call exc_info() in a function that does not itself handle an exception.

注意

Beginning with Python 2.2, such cycles are automatically reclaimed when garbage collection is enabled and they become unreachable, but it remains more efficient to avoid creating cycles.

sys. exc_clear ( ) ¶

This function clears all information relating to the current or last exception that occurred in the current thread. After calling this function, exc_info() will return three None values until another exception is raised in the current thread or the execution stack returns to a frame where another exception is being handled.

This function is only needed in only a few obscure situations. These include logging and error handling systems that report information on the last or current exception. This function can also be used to try to free resources and trigger object finalization, though no guarantee is made as to what objects will be freed, if any.

2.3 版新增。

sys. exc_type ¶

sys. exc_value ¶

sys. exc_traceback ¶

Deprecated since version 1.5: 使用 exc_info() 代替。

Since they are global variables, they are not specific to the current thread, so their use is not safe in a multi-threaded program. When no exception is being handled, exc_type 被设为 None and the other two are undefined.

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 自变量到 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 ，其中 X.Y is the version number of Python, for example 2.7 .

sys. executable ¶

给出 Python 解释器可执行二进制文件绝对路径的字符串，若在系统中这有意义。若 Python 无法检索到其可执行文件的真实路径， 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.

由于 exit() ultimately “only” raises an exception, it will only exit the process when called from the main thread, and the exception is not intercepted.

sys. exitfunc ¶

This value is not actually defined by the module, but can be set by the user (or by a program) to specify a clean-up action at program exit. When set, it should be a parameterless function. This function will be called when the interpreter exits. Only one function may be installed in this way; to allow multiple functions which will be called at termination, use the atexit 模块。

注意

The exit function is not called when the program is killed by a signal, when a Python fatal internal error is detected, or when os._exit() 被调用。

Deprecated since version 2.4: 使用 atexit 代替。

sys. flags ¶

The struct sequence flags 暴露命令行标志状态。属性只读。

属性	flag
debug	-d
py3k_warning	-3
division_warning	-Q
division_new	-Qnew
inspect	-i
interactive	-i
optimize	-O or -OO
dont_write_bytecode	-B
no_user_site	-s
no_site	-S
ignore_environment	-E
tabcheck	-t or -tt
verbose	-v
unicode	-U
bytes_warning	-b
hash_randomization	-R

2.6 版新增。

New in version 2.7.3: The hash_randomization 属性。

sys. float_info ¶

A structseq 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'
						

2.6 版新增。

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 2.7 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 2.7.

2.7 版新增。

sys. getcheckinterval ( ) ¶

返回解释器的校验间隔；见 setcheckinterval() .

2.3 版新增。

sys. getdefaultencoding ( ) ¶

Return the name of the current default string encoding used by the Unicode implementation.

2.0 版新增。

sys. getdlopenflags ( ) ¶

Return the current value of the flags that are used for dlopen() calls. The flag constants are defined in the dl and DLFCN modules. Availability: Unix.

2.2 版新增。

sys. getfilesystemencoding ( ) ¶

Return the name of the encoding used to convert Unicode filenames into system file names, or None if the system default encoding is used. The result value depends on the operating system:

• 在 Mac OS X，编码是 'utf-8' .

• On Unix, the encoding is the user’s preference according to the result of nl_langinfo(CODESET), or None 若 nl_langinfo(CODESET) failed.

• On Windows NT+, file names are Unicode natively, so no conversion is performed. getfilesystemencoding() still returns 'mbcs' , as this is the encoding that applications should use when they explicitly want to convert Unicode strings to byte strings that are equivalent when used as file names.

• On Windows 9x, the encoding is 'mbcs' .

2.3 版新增。

sys. getrefcount ( 对象 ) ¶

返回引用计数为 object 。一般来说，返回计数可能比期望大 1，因为它包含 (临时) 引用作为自变量在 getrefcount() .

sys. getrecursionlimit ( ) ¶

返回递归限制的当前值 (Python 解释器堆栈的最大深度)。此限制阻止导致 C 堆栈溢出和 Python 崩溃的无限递归。可以设置它通过 setrecursionlimit() .

sys. getsizeof ( 对象 [ , default ] ) ¶

返回对象的大小，以字节为单位。对象可以是任何类型的对象。所有内置对象会返回正确结果，但对于第 3 方扩展而言这不一定正确，因为它是特定实现。

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() 调用对象的 __sizeof__ method and adds an additional garbage collector overhead if the object is managed by the garbage collector.

2.6 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，返回堆栈顶部下多个调用帧对象。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 ( ) ¶

获取剖分析器函数如设置通过 setprofile() .

2.6 版新增。

sys. gettrace ( ) ¶

获取跟踪函数如设置通过 settrace() .

CPython 实现细节： 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.

2.6 版新增。

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 ，和 product_type . service_pack contains a string while 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 may be one of the following values:

常量	平台
0 (VER_PLATFORM_WIN32s)	Win32s on Windows 3.1
1 (VER_PLATFORM_WIN32_WINDOWS)	Windows 95/98/ME
2 (VER_PLATFORM_WIN32_NT)	Windows NT/2000/XP/x64
3 (VER_PLATFORM_WIN32_CE)	Windows CE

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.

可用性：Windows。

2.3 版新增。

2.7 版改变： Changed to a named tuple and added service_pack_minor , service_pack_major , suite_mask ，和 product_type .

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() 函数。 version_info value may be used for a more human-friendly encoding of the same information.

The hexversion is a 32-bit number with the following layout:

位数 (大端在前次序)	含义
1-8	PY_MAJOR_VERSION ( 2 in 2.1.0a3 )
9-16	PY_MINOR_VERSION ( 1 in 2.1.0a3 )
17-24	PY_MICRO_VERSION ( 0 in 2.1.0a3 )
25-28	PY_RELEASE_LEVEL ( 0xA 对于 Alpha， 0xB 对于 Beta， 0xC 对于发行候选和 0xF for final)
29-32	PY_RELEASE_SERIAL ( 3 in 2.1.0a3 ，0 对于最终发行)

因此 2.1.0a3 是十六进制 0x020100a3 .

1.5.2 版新增。

sys. long_info ¶

A struct sequence 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**long_info.bits_per_digit
sizeof_digit	size in bytes of the C type used to represent a digit

2.7 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 chapter pdb — Python 调试器 了解更多信息。)

The meaning of the variables is the same as that of the return values from exc_info() above. (Since there is only one interactive thread, thread-safety is not a concern for these variables, unlike for exc_type etc.)

sys. maxint ¶

The largest positive integer supported by Python’s regular integer type. This is at least 2**31-1. The largest negative integer is -maxint-1 — the asymmetry results from the use of 2’s complement binary arithmetic.

sys. maxsize ¶

The largest positive integer supported by the platform’s Py_ssize_t type, and thus the maximum size lists, strings, dicts, and many other containers can have.

sys. maxunicode ¶

An integer giving the largest supported code point for a Unicode character. The value of this depends on the configuration option that specifies whether Unicode characters are stored as UCS-2 or UCS-4.

sys. meta_path ¶

列表化的 finder 对象拥有 find_module() methods called to see if one of the objects can find the module to be imported. The find_module() method is called at least with the absolute name of the module being imported. If the module to be imported is contained in package then the parent package’s __path__ attribute is passed in as a second argument. The method returns None if the module cannot be found, else returns a loader .

sys.meta_path is searched before any implicit default finders or sys.path .

见 PEP 302 for the original specification.

sys. modules ¶

This is a dictionary that maps module names to modules which have already been loaded. This can be manipulated to force reloading of modules and other tricks. Note that removing a module from this dictionary is not the same as calling reload() on the corresponding module object.

sys. path ¶

指定模块搜索路径的字符串列表。初始化自环境变量 PYTHONPATH ，加从属安装默认。

在程序启动时被初始化，此列表的第一项， 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 插入条目作为结果对于 PYTHONPATH .

A program is free to modify this list for its own purposes.

Changed in version 2.3: Unicode strings are no longer ignored.

另请参阅

模块 site 这描述如何使用 .pth 文件扩展 sys.path .

sys. path_hooks ¶

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

最初的指定在 PEP 302 .

sys. path_importer_cache ¶

字典充当缓存对于 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 explicit finder is found on sys.path_hooks then None is stored to represent the implicit default finder should be used. If the path is not an existing path then imp.NullImporter 有设置。

最初的指定在 PEP 302 .

sys. platform ¶

This string contains a platform identifier that can be used to append platform-specific components to sys.path ，例如。

For most Unix systems, 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' , 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...
							

Changed in version 2.7.3: Since lots of code check for sys.platform == 'linux2' , and there is no essential change between Linux 2.x and 3.x, sys.platform is always set to 'linux2' , even on Linux 3.x. In Python 3.3 and later, the value will always be set to 'linux' , so it is recommended to always use the startswith idiom presented above.

对于其它系统，值是：

系统	platform 值
Linux (2.x and 3.x)	'linux2'
Windows	'win32'
Windows/Cygwin	'cygwin'
Mac OS X	'darwin'
OS/2	'os2'
OS/2 EMX	'os2emx'
RiscOS	'riscos'
AtheOS	'atheos'

另请参阅

os.name 拥有更粗的粒度。 os.uname() 给出系统从属版本信息。

The platform 模块提供系统身份的详细校验。

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 自变量到 configure script. The main collection of Python library modules is installed in the directory prefix/lib/pythonX.Y while the platform independent header files (all except pyconfig.h ) are stored in prefix/include/pythonX.Y ，其中 X.Y is the version number of Python, for example 2.7 .

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. py3kwarning ¶

Bool containing the status of the Python 3 warning flag. It’s True when Python is started with the -3 option. (This should be considered read-only; setting it to a different value doesn’t have an effect on Python 3 warnings.)

2.6 版新增。

sys. setcheckinterval ( interval ) ¶

设置解释器的 "检查间隔"。此整数值确定解释器检查周期性事物 (譬如：线程切换和信号处理程序) 的频率。默认为 100 ，意味着每隔 100 条 Python 虚拟指令履行一次检查。将它设为较大值，可以提高使用线程的程序性能。将它设为值 <= 0 检查每条虚拟指令，最大化响应速度及开销。

sys. setdefaultencoding ( 名称 ) ¶

Set the current default string encoding used by the Unicode implementation. If name does not match any available encoding, LookupError is raised. This function is only intended to be used by the site module implementation and, where needed, by sitecustomize . Once used by the site module, it is removed from the sys module’s namespace.

2.0 版新增。

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(dl.RTLD_NOW | dl.RTLD_GLOBAL) . Symbolic names for the flag modules can be either found in the dl module, or in the DLFCN module. If DLFCN is not available, it can be generated from /usr/include/dlfcn.h 使用 h2py script. Availability: Unix.

2.2 版新增。

sys. setprofile ( profilefunc ) ¶

Set the system’s profile function, which allows you to implement a Python source code profiler in Python. See chapter Python 剖分析器 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 .

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'

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 是 C 函数对象。

'c_return'

A C function has returned. arg 是 C 函数对象。

'c_exception'

C 函数引发异常。 arg 是 C 函数对象。

sys. setrecursionlimit ( limit ) ¶

将 Python 解释器堆栈的最大深度设为 limit 。此限制阻止导致 C 堆栈溢出和 Python 崩溃的无限递归。

The highest possible limit is platform-dependent. A user may need to set the limit higher when she has 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.

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.

跟踪函数是援引 (采用 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'

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.

'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'

出现异常。调用局部跟踪函数； arg 是元组 (exception, value, traceback) ；返回值指定新的本地跟踪函数。

注意，由于异常沿调用者链向下传播， 'exception' 事件会在每级生成。

For more information on code and frame objects, refer to 标准类型层次结构 .

CPython 实现细节： 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.

sys. settscdump ( on_flag ) ¶

Activate dumping of VM measurements using the Pentium timestamp counter, if on_flag is true. Deactivate these dumps if on_flag is off. The function is available only if Python was compiled with --with-tsc . To understand the output of this dump, read Python/ceval.c in the Python sources.

2.4 版新增。

CPython 实现细节： This function is intimately bound to CPython implementation details and thus not likely to be implemented elsewhere.

sys. stdin ¶

sys. stdout ¶

sys. stderr ¶

File objects corresponding to the interpreter’s standard input, output and error streams. stdin is used for all interpreter input except for scripts but including calls to input() and raw_input() . stdout 用于输出源自 print and 表达式 语句及提示对于 input() and raw_input() . The interpreter’s own prompts and (almost all of) its error messages go to stderr . stdout and stderr needn’t be built-in file objects: any object is acceptable as long as it has a write() method that takes a string argument. (Changing these objects doesn’t affect the standard I/O streams of processes executed by os.popen() , os.system() 或 exec*() family of functions in the os 模块。)

sys. __stdin__ ¶

sys. __stdout__ ¶

sys. __stderr__ ¶

这些对象包含原始值的 stdin , stderr and stdout 当程序启动时。在定稿期间使用它们，可以打印到实际标准流不管是否 sys.std* 对象已被重定向。

还可以用于将实际文件还原到已知工作文件对象，若它们被破坏对象所覆写。不管怎样，首选方式是在替换它之前明确保存先前流，再还原保存对象。

sys. subversion ¶

A triple (repo, branch, version) representing the Subversion information of the Python interpreter. repo is the name of the repository, 'CPython' . branch is a string of one of the forms 'trunk' , 'branches/name' or 'tags/name' . version is the output of svnversion , if the interpreter was built from a Subversion checkout; it contains the revision number (range) and possibly a trailing ‘M’ if there were local modifications. If the tree was exported (or svnversion was not available), it is the revision of Include/patchlevel.h if the branch is a tag. Otherwise, it is None .

2.5 版新增。

注意

Python is now developed using Git. In recent Python 2.7 bugfix releases, subversion therefore contains placeholder information. It is removed in Python 3.3.

sys. tracebacklimit ¶

当设为整数值时，此变量确定打印回溯信息的最大级数，当发生未处理异常时。默认为 1000 。当设为 0 或更少，所有回溯信息被抑制且只打印异常类型和值。

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.

2.3 版新增。

sys. version_info ¶

包含版本编号 5 分量的元组： major , minor , micro , releaselevel ，和 serial 。所有值除了 releaselevel 都是整数；releaselevel 为 '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 依此类推。

2.0 版新增。

2.7 版改变： Added named component attributes

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.

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 .

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