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Python Library Reference |  |
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Python Library Reference | |
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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[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 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.
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 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.
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 string or 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.
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.
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.
'/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].
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.
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-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.
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-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 inserted before the entries
inserted as a result of PYTHONPATH.
'sunos5' or
'linux1'. This can be used to append platform-specific
components to path, for instance.
'/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].
'>>> ' 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.
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 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.
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 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,
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.
1000. When set
to 0 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'. The version_info
value corresponding to the Python version 2.0 is (2, 0, 0,
'final', 0).
New in version 2.0.
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Python Library Reference | |
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