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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.
- argv
- The list of command line arguments passed to a Python script.
argv[0] is
the script name (it is operating system dependent whether this is a full pathname or not).
If the command was executed using the -c command line option to
the interpreter, argv[0] is set to the string '-c'. If no script
name was passed to the Python interpreter, argv has zero length.
- byteorder
- An indicator of the native byte order. This will have the value
'big' on
big-endian (most-signigicant byte first) platforms, and 'little' on little-endian
(least-significant byte first) platforms. New in version 2.0.
- 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.)
- copyright
- A string containing the copyright pertaining to the Python interpreter.
- dllhandle
- Integer specifying the handle of the Python DLL. Availability: Windows.
-
- If value is not
None, this function prints it to sys.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 to sys.displayhook.
-
| excepthook( |
type, value, traceback) |
- This function prints out a given traceback and exception to
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.
- __displayhook__
-
- __excepthook__
- These objects contain the original values of
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.
-
- 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.
If no exception is being handled anywhere on the stack, a tuple containing three None
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 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 gets a traceback object (see the Reference Manual)
which encapsulates the call stack at the point where the exception originally occurred.
If 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.
Warning: 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. 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.
-
- This function clears all information relating to the current or last exception that
occured 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. New
in version 2.3.
- exc_type
-
- exc_value
-
- exc_traceback
-
Deprecated since release 1.5. Use exc_info() instead.
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 to None and the other two are undefined.
- 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/pythonversion/config', and shared library modules are installed
in exec_prefix + '/lib/pythonversion/lib-dynload', where version
is equal to version[:3].
- executable
- A string giving the name of the executable binary for the Python interpreter, on systems
where this makes sense.
-
- Exit from Python. This is implemented by raising the SystemExit
exception, so cleanup actions specified by finally clauses of try
statements are honored, and it is possible to intercept the exit attempt at an outer
level. 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 sys.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.
- 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
module. Note: 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() is called.
-
- Return the interpreter's ``check interval''; see setcheckinterval().
New in version 2.3.
-
- Return the name of the current default string encoding used by the Unicode
implementation. New in version 2.0.
-
- 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. New in version
2.2.
-
- 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:
- On Windows 9x, the encoding is ``mbcs''.
- On Mac OS X, the encoding is ``utf-8''.
- On Unix, the encoding is the user's preference according to the result of
nl_langinfo(CODESET), or None if the nl_langinfo(CODESET) failed.
- On Windows NT+, file names are Unicode natively, so no conversion is performed.
New in version 2.3.
-
- 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().
-
- 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 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.
This function should be used for internal and specialized purposes only.
-
- Return a tuple containing five components, describing the Windows version currently
running. The elements are major, minor, build, platform,
and text. text contains a string while all other values are
integers.
platform may be one of the following values:
- 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
- 3 (VER_PLATFORM_WIN32_CE)
- Windows CE.
This function wraps the Win32 GetVersionEx() function; see
the Microsoft Documentation for more information about these fields.
Availability: Windows. New in version 2.3.
- 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 version_info value may be used for a more human-friendly
encoding of the same information. New in version 1.5.2.
- last_type
-
- last_value
-
- 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 9, ``The Python Debugger,'' for more
information.)
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.)
- 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.
- 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.
- 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.
- 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.
Changed in version 2.3: Unicode strings are no longer
ignored..
- platform
- This string contains a platform identifier, e.g.
'sunos5' or 'linux1'.
This can be used to append platform-specific components to path, for
instance.
- 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/pythonversion' while the
platform independent header files (all except pyconfig.h) are
stored in prefix + '/include/pythonversion', where version
is equal to version[:3].
- ps1
-
- 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.
-
| 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.
-
| setdefaultencoding( |
name) |
- 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. New in version 2.0.
-
- 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 using the h2py script.
Availability: Unix. New in version 2.2.
-
- Set the system's profile function,
which allows you to implement a Python source code profiler in Python.
See chapter 10 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 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.
-
| 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 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.
-
- Set the system's trace function,
which allows you to implement a Python source code debugger in Python. See section 9.2, ``How It Works,'' in the chapter on the
Python debugger.
The function is thread-specific; for a debugger to support multiple threads, it must
be registered using settrace() for each thread being debugged.
- stdin
-
- stdout
-
- 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 is used for the output of print and
expression statements and for the prompts of 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() or the exec*() family of
functions in the os module.)
- __stdin__
-
- __stdout__
-
- __stderr__
- These objects contain the original values of
stdin, stderr and
stdout at the start of the program. They are used during finalization, and
could be useful to restore the actual files to known working file objects in case they
have been overwritten with a broken object.
- 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.
- version
- A string containing the version number of the Python interpreter plus additional
information on the build number and compiler used. It has a value of the form
'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)]'
- api_version
- The C API version for this interpreter. Programmers may find this useful when debugging
version conflicts between Python and extension modules. New in
version 2.3.
- version_info
- A tuple containing the five components of the version number: major, minor,
micro, releaselevel, and serial. All values except releaselevel
are integers; the release level is
'alpha', 'beta', 'candidate',
or 'final'. The version_info value corresponding to the Python
version 2.0 is (2, 0, 0, 'final', 0). New in
version 2.0.
- 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.
- 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.
See Also:
- Module site:
- This describes how to use .pth files to extend
sys.path.
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