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This module provides access to some variables used or maintained by theinterpreter and to functions that interact strongly with the interpreter.It is always available.
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 has zero length.'big' on big-endian (most-signigicant byte first) platforms, and'little' on little-endian (least-significant byte first) platforms.New in version 2.0.modules.keys() only lists the imported modules.)None, this function prints it tosys.stdout, and saves it in__builtin__._.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 tosys.displayhook.
sys.stderr.When an exception is raised and uncaught, the interpreter callssys.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 tosys.excepthook.
displayhook andexcepthook at the start of the program. They are saved so thatdisplayhook andexcepthook can be restored in case they happen to get replaced with broken objects.If no exception is being handled anywhere on the stack, a tuple containing threeNone values is returned. Otherwise, the values returned are(type,value,traceback). Their meaning is:type gets the exception type of the exception being handled (a string or class object);value gets the exception parameter (itsassociated value or the second argument toraise, which is always a class instance if the exception type is a class object);traceback gets a traceback object (see the Reference Manual) which encapsulates the call stack at the point where the exception originally occurred.
Warning:Assigning thetraceback 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 likeexctype, 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 atry ...finally statement) or to callexc_info() in a function that does not itself handle an exception.Note: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.
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 is set toNone and the other two are undefined.
'/usr/local'. This can be set at build time with the--exec-prefix argument to theconfigure script. Specifically, all configuration files (e.g. thepyconfig.h header file) are installed in the directoryexec_prefix + '/lib/pythonversion/config', and shared library modules are installed inexec_prefix + '/lib/pythonversion/lib-dynload', whereversion is equal toversion[:3].None is equivalent to passing zero, and any other object is printed tosys.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.os._exit() is called.This function should be used for internal and specialized purposes only.
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-inhex() function. Theversion_info value may be used for a more human-friendly encoding of the same information.New in version 1.5.2.
The meaning of the variables is the same as that of the return values fromexc_info() above. (Since there is only one interactive thread, thread-safety is not a concern for these variables, unlike forexc_type etc.)
-maxint-1 -- the asymmetry results from the use of 2's complement binary arithmetic.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 insertedbefore the entries inserted as a result ofPYTHONPATH.
'sunos5' or'linux1'. This can be used to append platform-specific components topath, for instance.'/usr/local'. This can be set at build time with the--prefix argument to theconfigure script. The main collection of Python library modules is installed in the directoryprefix + '/lib/pythonversion' while the platform independent header files (all exceptpyconfig.h) are stored inprefix + '/include/pythonversion', whereversion is equal toversion[:3].'>>> ' and'... '. If a non-string object is assigned to either variable, itsstr() is re-evaluated each time the interpreter prepares to read a new interactive command; this can be used to implement a dynamic prompt.10, meaning the check is performed every 10 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.sys.setdlopenflags(0). To share symbols across extension modules, call assys.setdlopenflags(dl.RTLD_NOW | dl.RTLD_GLOBAL). Symbolic names for the flag modules can be either found in thedl module, or in theDLFCN module. IfDLFCN is not available, it can be generated from/usr/include/dlfcn.h using theh2py script. Availability: Unix.New in version 2.2.None.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.
stdin is used for all interpreter input except for scripts but including calls toinput() andraw_input() .stdout is used for the output ofprint and expression statements and for the prompts ofinput() andraw_input(). The interpreter's own prompts and (almost all of) its error messages go tostderr.stdout andstderr needn't be built-in file objects: any object is acceptable as long as it has awrite() method that takes a string argument. (Changing these objects doesn't affect the standard I/O streams of processes executed byos.popen(),os.system() or theexec*() family of functions in theos module.)stdin,stderr andstdout at the start of the program. They are used during finalization, and could be useful to restore the actual files to known working file objects in case they have been overwritten with a broken object.1000. When set to0 or less, all traceback information is suppressed and only the exception type and value are printed.'version (#build_number,build_date,build_time) [compiler]'. The first three characters are used to identify the version in the installation directories (where appropriate on each platform). An example:>>> import sys>>> sys.version'1.5.2 (#0 Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)]'
'alpha','beta','candidate', or'final'. Theversion_info value corresponding to the Python version 2.0 is(2, 0, 0, 'final', 0).New in version 2.0. | | | Python Library Reference | | | |