mirror of
https://github.com/python/cpython.git
synced 2025-10-31 02:15:10 +00:00
713d3039dc
:option: is used to create a link to an option of python, not to mark up any instance of any arbitrary command-line option. These were changed to ````. For modules which do have a command-line interface, lists of options have been properly marked up with the program/cmdoption directives combo. Options defined in such blocks can be linked to with :option: later in the same file, they won’t link to an option of python. Finally, the markup of command-line fragments in optparse.rst has been cleaned to use ``x`` instead of ``"x"``, keeping that latter form for actual Python strings. Patch by Eli Bendersky and Éric Araujo.
1005 lines
44 KiB
ReStructuredText
1005 lines
44 KiB
ReStructuredText
:mod:`sys` --- System-specific parameters and functions
|
|
=======================================================
|
|
|
|
.. module:: sys
|
|
:synopsis: Access system-specific parameters and functions.
|
|
|
|
|
|
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.
|
|
|
|
|
|
.. data:: abiflags
|
|
|
|
On POSIX systems where Python is build with the standard ``configure``
|
|
script, this contains the ABI flags as specified by :pep:`3149`.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. data:: 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 :option:`-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[0]`` is the empty string.
|
|
|
|
To loop over the standard input, or the list of files given on the
|
|
command line, see the :mod:`fileinput` module.
|
|
|
|
|
|
.. data:: 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.
|
|
|
|
|
|
.. data:: 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``.
|
|
|
|
|
|
.. data:: 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.)
|
|
|
|
|
|
.. function:: call_tracing(func, args)
|
|
|
|
Call ``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.
|
|
|
|
|
|
.. data:: copyright
|
|
|
|
A string containing the copyright pertaining to the Python interpreter.
|
|
|
|
|
|
.. function:: _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.
|
|
|
|
|
|
.. function:: _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 :mod:`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.
|
|
|
|
|
|
.. data:: dllhandle
|
|
|
|
Integer specifying the handle of the Python DLL. Availability: Windows.
|
|
|
|
|
|
.. function:: displayhook(value)
|
|
|
|
If *value* is not ``None``, this function prints it to ``sys.stdout``, and saves
|
|
it in ``builtins._``.
|
|
|
|
``sys.displayhook`` is called on the result of evaluating an :term:`expression`
|
|
entered in an interactive Python session. The display of these values can be
|
|
customized by assigning another one-argument function to ``sys.displayhook``.
|
|
|
|
|
|
.. function:: 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``.
|
|
|
|
|
|
.. data:: __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.
|
|
|
|
|
|
.. function:: 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
|
|
an except clause." For any stack frame, only information about the exception
|
|
being currently handled is accessible.
|
|
|
|
.. index:: object: traceback
|
|
|
|
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 type of the
|
|
exception being handled (a subclass of :exc:`BaseException`); *value* gets
|
|
the exception instance (an instance of the exception type); *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. 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 :keyword:`try`
|
|
... :keyword:`finally` statement) or to call :func:`exc_info` in a
|
|
function that does not itself handle an exception.
|
|
|
|
Such cycles are normally automatically reclaimed when garbage collection
|
|
is enabled and they become unreachable, but it remains more efficient to
|
|
avoid creating cycles.
|
|
|
|
|
|
.. data:: 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
|
|
:program:`configure` script. Specifically, all configuration files (e.g. the
|
|
:file:`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]``.
|
|
|
|
|
|
.. data:: executable
|
|
|
|
A string giving the name of the executable binary for the Python interpreter, on
|
|
systems where this makes sense.
|
|
|
|
|
|
.. function:: exit([arg])
|
|
|
|
Exit from Python. This is implemented by raising the :exc:`SystemExit`
|
|
exception, so cleanup actions specified by finally clauses of :keyword:`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 :data:`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 :func:`exit` ultimately "only" raises an exception, it will only exit
|
|
the process when called from the main thread, and the exception is not
|
|
intercepted.
|
|
|
|
|
|
.. data:: flags
|
|
|
|
The struct sequence *flags* exposes the status of command line flags. The
|
|
attributes are read only.
|
|
|
|
+------------------------------+------------------------------------------+
|
|
| attribute | flag |
|
|
+==============================+==========================================+
|
|
| :const:`debug` | -d |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`division_warning` | -Q |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`inspect` | -i |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`interactive` | -i |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`optimize` | -O or -OO |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`dont_write_bytecode` | -B |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`no_user_site` | -s |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`no_site` | -S |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`ignore_environment` | -E |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`verbose` | -v |
|
|
+------------------------------+------------------------------------------+
|
|
| :const:`bytes_warning` | -b |
|
|
+------------------------------+------------------------------------------+
|
|
|
|
|
|
.. data:: 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 :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.
|
|
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| attribute | float.h macro | explanation |
|
|
+=====================+================+==================================================+
|
|
| :const:`epsilon` | DBL_EPSILON | difference between 1 and the least value greater |
|
|
| | | than 1 that is representable as a float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`dig` | DBL_DIG | maximum number of decimal digits that can be |
|
|
| | | faithfully represented in a float; see below |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`mant_dig` | DBL_MANT_DIG | float precision: the number of base-``radix`` |
|
|
| | | digits in the significand of a float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`max` | DBL_MAX | maximum representable finite float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`max_exp` | DBL_MAX_EXP | maximum integer e such that ``radix**(e-1)`` is |
|
|
| | | a representable finite float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`max_10_exp` | DBL_MAX_10_EXP | maximum integer e such that ``10**e`` is in the |
|
|
| | | range of representable finite floats |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`min` | DBL_MIN | minimum positive normalized float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`min_exp` | DBL_MIN_EXP | minimum integer e such that ``radix**(e-1)`` is |
|
|
| | | a normalized float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`min_10_exp` | DBL_MIN_10_EXP | minimum integer e such that ``10**e`` is a |
|
|
| | | normalized float |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`radix` | FLT_RADIX | radix of exponent representation |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
| :const:`rounds` | FLT_ROUNDS | constant representing rounding mode |
|
|
| | | used for arithmetic operations |
|
|
+---------------------+----------------+--------------------------------------------------+
|
|
|
|
The attribute :attr:`sys.float_info.dig` needs further explanation. If
|
|
``s`` is any string representing a decimal number with at most
|
|
:attr:`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 :attr:`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'
|
|
|
|
.. data:: float_repr_style
|
|
|
|
A string indicating how the :func:`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.
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
.. function:: getcheckinterval()
|
|
|
|
Return the interpreter's "check interval"; see :func:`setcheckinterval`.
|
|
|
|
.. deprecated:: 3.2
|
|
Use :func:`getswitchinterval` instead.
|
|
|
|
|
|
.. function:: getdefaultencoding()
|
|
|
|
Return the name of the current default string encoding used by the Unicode
|
|
implementation.
|
|
|
|
|
|
.. function:: getdlopenflags()
|
|
|
|
Return the current value of the flags that are used for :c:func:`dlopen` calls.
|
|
The flag constants are defined in the :mod:`ctypes` and :mod:`DLFCN` modules.
|
|
Availability: Unix.
|
|
|
|
|
|
.. function:: getfilesystemencoding()
|
|
|
|
Return the name of the encoding used to convert Unicode filenames into
|
|
system file names. The result value depends on the operating system:
|
|
|
|
* 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 ``'utf-8'`` if ``nl_langinfo(CODESET)`` failed.
|
|
|
|
* On Windows NT+, file names are Unicode natively, so no conversion is
|
|
performed. :func:`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'``.
|
|
|
|
.. versionchanged:: 3.2
|
|
On Unix, use ``'utf-8'`` instead of ``None`` if ``nl_langinfo(CODESET)``
|
|
failed. :func:`getfilesystemencoding` result cannot be ``None``.
|
|
|
|
|
|
.. function:: 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 :func:`getrefcount`.
|
|
|
|
|
|
.. function:: 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
|
|
:func:`setrecursionlimit`.
|
|
|
|
|
|
.. function:: 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.
|
|
|
|
If given, *default* will be returned if the object does not provide means to
|
|
retrieve the size. Otherwise a :exc:`TypeError` will be raised.
|
|
|
|
:func:`getsizeof` calls the object's ``__sizeof__`` method and adds an
|
|
additional garbage collector overhead if the object is managed by the garbage
|
|
collector.
|
|
|
|
|
|
.. function:: getswitchinterval()
|
|
|
|
Return the interpreter's "thread switch interval"; see
|
|
:func:`setswitchinterval`.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. function:: _getframe([depth])
|
|
|
|
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, :exc:`ValueError` is raised. The default
|
|
for *depth* is zero, returning the frame at the top of the call stack.
|
|
|
|
.. impl-detail::
|
|
|
|
This function should be used for internal and specialized purposes only.
|
|
It is not guaranteed to exist in all implementations of Python.
|
|
|
|
|
|
.. function:: getprofile()
|
|
|
|
.. index::
|
|
single: profile function
|
|
single: profiler
|
|
|
|
Get the profiler function as set by :func:`setprofile`.
|
|
|
|
|
|
.. function:: gettrace()
|
|
|
|
.. index::
|
|
single: trace function
|
|
single: debugger
|
|
|
|
Get the trace function as set by :func:`settrace`.
|
|
|
|
.. impl-detail::
|
|
|
|
The :func:`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.
|
|
|
|
|
|
.. function:: 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*, and *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]`` is equivalent to
|
|
``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:
|
|
|
|
+-----------------------------------------+-------------------------+
|
|
| Constant | Platform |
|
|
+=========================================+=========================+
|
|
| :const:`0 (VER_PLATFORM_WIN32s)` | Win32s on Windows 3.1 |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`1 (VER_PLATFORM_WIN32_WINDOWS)` | Windows 95/98/ME |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`2 (VER_PLATFORM_WIN32_NT)` | Windows NT/2000/XP/x64 |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`3 (VER_PLATFORM_WIN32_CE)` | Windows CE |
|
|
+-----------------------------------------+-------------------------+
|
|
|
|
*product_type* may be one of the following values:
|
|
|
|
+---------------------------------------+---------------------------------+
|
|
| Constant | Meaning |
|
|
+=======================================+=================================+
|
|
| :const:`1 (VER_NT_WORKSTATION)` | The system is a workstation. |
|
|
+---------------------------------------+---------------------------------+
|
|
| :const:`2 (VER_NT_DOMAIN_CONTROLLER)` | The system is a domain |
|
|
| | controller. |
|
|
+---------------------------------------+---------------------------------+
|
|
| :const:`3 (VER_NT_SERVER)` | The system is a server, but not |
|
|
| | a domain controller. |
|
|
+---------------------------------------+---------------------------------+
|
|
|
|
|
|
This function wraps the Win32 :c:func:`GetVersionEx` function; see the
|
|
Microsoft documentation on :c:func:`OSVERSIONINFOEX` for more information
|
|
about these fields.
|
|
|
|
Availability: Windows.
|
|
|
|
.. versionchanged:: 3.2
|
|
Changed to a named tuple and added *service_pack_minor*,
|
|
*service_pack_major*, *suite_mask*, and *product_type*.
|
|
|
|
|
|
.. data:: hash_info
|
|
|
|
A structseq giving parameters of the numeric hash implementation. For
|
|
more details about hashing of numeric types, see :ref:`numeric-hash`.
|
|
|
|
+---------------------+--------------------------------------------------+
|
|
| attribute | explanation |
|
|
+=====================+==================================================+
|
|
| :const:`width` | width in bits used for hash values |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`modulus` | prime modulus P used for numeric hash scheme |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`inf` | hash value returned for a positive infinity |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`nan` | hash value returned for a nan |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`imag` | multiplier used for the imaginary part of a |
|
|
| | complex number |
|
|
+---------------------+--------------------------------------------------+
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. data:: 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 :func:`hex` function. The
|
|
``version_info`` value may be used for a more human-friendly encoding of the
|
|
same information.
|
|
|
|
|
|
.. data:: int_info
|
|
|
|
A struct sequence that holds information about Python's
|
|
internal representation of integers. The attributes are read only.
|
|
|
|
+-------------------------+----------------------------------------------+
|
|
| attribute | explanation |
|
|
+=========================+==============================================+
|
|
| :const:`bits_per_digit` | number of bits held in each digit. Python |
|
|
| | integers are stored internally in base |
|
|
| | ``2**int_info.bits_per_digit`` |
|
|
+-------------------------+----------------------------------------------+
|
|
| :const:`sizeof_digit` | size in bytes of the C type used to |
|
|
| | represent a digit |
|
|
+-------------------------+----------------------------------------------+
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
.. function:: 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 :func:`intern` around to benefit from it.
|
|
|
|
|
|
.. data:: 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 :mod:`pdb` module for
|
|
more information.)
|
|
|
|
The meaning of the variables is the same as that of the return values from
|
|
:func:`exc_info` above.
|
|
|
|
|
|
.. data:: maxsize
|
|
|
|
An integer giving the maximum value a variable of type :c: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.
|
|
|
|
|
|
.. data:: 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.
|
|
|
|
|
|
.. data:: meta_path
|
|
|
|
A list of :term:`finder` objects that have their :meth:`find_module`
|
|
methods called to see if one of the objects can find the module to be
|
|
imported. The :meth:`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 :attr:`__path__` attribute
|
|
is passed in as a second argument. The method returns :keyword:`None` if
|
|
the module cannot be found, else returns a :term:`loader`.
|
|
|
|
:data:`sys.meta_path` is searched before any implicit default finders or
|
|
:data:`sys.path`.
|
|
|
|
See :pep:`302` for the original specification.
|
|
|
|
|
|
.. data:: 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.
|
|
|
|
|
|
.. data:: path
|
|
|
|
.. index:: triple: module; search; path
|
|
|
|
A list of strings that specifies the search path for modules. Initialized from
|
|
the environment variable :envvar:`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 :envvar:`PYTHONPATH`.
|
|
|
|
A program is free to modify this list for its own purposes.
|
|
|
|
|
|
.. seealso::
|
|
Module :mod:`site` This describes how to use .pth files to extend
|
|
:data:`sys.path`.
|
|
|
|
|
|
.. data:: path_hooks
|
|
|
|
A list of callables that take a path argument to try to create a
|
|
:term:`finder` for the path. If a finder can be created, it is to be
|
|
returned by the callable, else raise :exc:`ImportError`.
|
|
|
|
Originally specified in :pep:`302`.
|
|
|
|
|
|
.. data:: path_importer_cache
|
|
|
|
A dictionary acting as a cache for :term:`finder` objects. The keys are
|
|
paths that have been passed to :data:`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 :data:`sys.path_hooks` then :keyword:`None` is
|
|
stored to represent the implicit default finder should be used. If the path
|
|
is not an existing path then :class:`imp.NullImporter` is set.
|
|
|
|
Originally specified in :pep:`302`.
|
|
|
|
|
|
.. data:: platform
|
|
|
|
This string contains a platform identifier that can be used to append
|
|
platform-specific components to :data:`sys.path`, for instance.
|
|
|
|
For 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'`` or ``'linux2'``, *at the time when Python was built*.
|
|
For other systems, the values are:
|
|
|
|
================ ===========================
|
|
System :data:`platform` value
|
|
================ ===========================
|
|
Windows ``'win32'``
|
|
Windows/Cygwin ``'cygwin'``
|
|
Mac OS X ``'darwin'``
|
|
OS/2 ``'os2'``
|
|
OS/2 EMX ``'os2emx'``
|
|
================ ===========================
|
|
|
|
|
|
.. data:: 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 :program:`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 :file:`pyconfig.h`) are
|
|
stored in ``prefix + '/include/pythonversion'``, where *version* is equal to
|
|
``version[:3]``.
|
|
|
|
|
|
.. data:: ps1
|
|
ps2
|
|
|
|
.. index::
|
|
single: interpreter prompts
|
|
single: prompts, interpreter
|
|
|
|
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 :func:`str` is re-evaluated each time the
|
|
interpreter prepares to read a new interactive command; this can be used to
|
|
implement a dynamic prompt.
|
|
|
|
|
|
.. data:: dont_write_bytecode
|
|
|
|
If this is true, Python won't try to write ``.pyc`` or ``.pyo`` 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.
|
|
|
|
|
|
.. function:: 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.
|
|
|
|
.. deprecated:: 3.2
|
|
This function doesn't have an effect anymore, as the internal logic for
|
|
thread switching and asynchronous tasks has been rewritten. Use
|
|
:func:`setswitchinterval` instead.
|
|
|
|
|
|
.. function:: setdlopenflags(n)
|
|
|
|
Set the flags used by the interpreter for :c:func:`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(ctypes.RTLD_GLOBAL)``. Symbolic names for the
|
|
flag modules can be either found in the :mod:`ctypes` module, or in the :mod:`DLFCN`
|
|
module. If :mod:`DLFCN` is not available, it can be generated from
|
|
:file:`/usr/include/dlfcn.h` using the :program:`h2py` script. Availability:
|
|
Unix.
|
|
|
|
.. function:: setprofile(profilefunc)
|
|
|
|
.. index::
|
|
single: profile function
|
|
single: profiler
|
|
|
|
Set the system's profile function, which allows you to implement a Python source
|
|
code profiler in Python. See chapter :ref:`profile` for more information on the
|
|
Python profiler. The system's profile function is called similarly to the
|
|
system's trace function (see :func:`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``.
|
|
|
|
|
|
.. function:: 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.
|
|
|
|
|
|
.. function:: 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.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. function:: settrace(tracefunc)
|
|
|
|
.. index::
|
|
single: trace function
|
|
single: debugger
|
|
|
|
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
|
|
:func:`settrace` for each thread being debugged.
|
|
|
|
Trace functions should have three arguments: *frame*, *event*, and
|
|
*arg*. *frame* is the current stack frame. *event* is a string: ``'call'``,
|
|
``'line'``, ``'return'``, ``'exception'``, ``'c_call'``, ``'c_return'``, or
|
|
``'c_exception'``. *arg* depends on the event type.
|
|
|
|
The trace function is invoked (with *event* set to ``'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.
|
|
|
|
The events have the following meaning:
|
|
|
|
``'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
|
|
:file:`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'``
|
|
An exception has occurred. The local trace function is called; *arg* is a
|
|
tuple ``(exception, value, traceback)``; the return value specifies the
|
|
new local trace function.
|
|
|
|
``'c_call'``
|
|
A C function is about to be called. This may be an extension function or
|
|
a built-in. *arg* is the C function object.
|
|
|
|
``'c_return'``
|
|
A C function has returned. *arg* is the C function object.
|
|
|
|
``'c_exception'``
|
|
A C function has raised an exception. *arg* is the C function object.
|
|
|
|
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 :ref:`types`.
|
|
|
|
.. impl-detail::
|
|
|
|
The :func:`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.
|
|
|
|
|
|
.. function:: 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 :file:`Python/ceval.c` in the Python sources.
|
|
|
|
.. impl-detail::
|
|
This function is intimately bound to CPython implementation details and
|
|
thus not likely to be implemented elsewhere.
|
|
|
|
|
|
.. data:: stdin
|
|
stdout
|
|
stderr
|
|
|
|
:term:`File objects <file object>` 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 :func:`input`. ``stdout`` is used
|
|
for the output of :func:`print` and :term:`expression` statements and for the
|
|
prompts of :func:`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 :meth:`write` method that takes a string argument. (Changing these
|
|
objects doesn't affect the standard I/O streams of processes executed by
|
|
:func:`os.popen`, :func:`os.system` or the :func:`exec\*` family of functions in
|
|
the :mod:`os` module.)
|
|
|
|
The standard streams are in text mode by default. To write or read binary
|
|
data to these, use the underlying binary buffer. For example, to write bytes
|
|
to :data:`stdout`, use ``sys.stdout.buffer.write(b'abc')``. Using
|
|
:meth:`io.TextIOBase.detach` streams can be made binary by default. This
|
|
function sets :data:`stdin` and :data:`stdout` to binary::
|
|
|
|
def make_streams_binary():
|
|
sys.stdin = sys.stdin.detach()
|
|
sys.stdout = sys.stdout.detach()
|
|
|
|
Note that the streams can be replaced with objects (like
|
|
:class:`io.StringIO`) that do not support the
|
|
:attr:`~io.BufferedIOBase.buffer` attribute or the
|
|
:meth:`~io.BufferedIOBase.detach` method and can raise :exc:`AttributeError`
|
|
or :exc:`io.UnsupportedOperation`.
|
|
|
|
|
|
.. data:: __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 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.
|
|
|
|
.. note::
|
|
Under some conditions ``stdin``, ``stdout`` and ``stderr`` as well as the
|
|
original values ``__stdin__``, ``__stdout__`` and ``__stderr__`` can be
|
|
None. It is usually the case for Windows GUI apps that aren't connected
|
|
to a console and Python apps started with :program:`pythonw`.
|
|
|
|
|
|
.. data:: 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.
|
|
|
|
|
|
.. data:: 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 :data:`version_info` and the functions provided by the
|
|
:mod:`platform` module.
|
|
|
|
|
|
.. data:: api_version
|
|
|
|
The C API version for this interpreter. Programmers may find this useful when
|
|
debugging version conflicts between Python and extension modules.
|
|
|
|
|
|
.. data:: 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)``. The components can also be accessed by name,
|
|
so ``sys.version_info[0]`` is equivalent to ``sys.version_info.major``
|
|
and so on.
|
|
|
|
.. versionchanged:: 3.1
|
|
Added named component attributes.
|
|
|
|
.. data:: warnoptions
|
|
|
|
This is an implementation detail of the warnings framework; do not modify this
|
|
value. Refer to the :mod:`warnings` module for more information on the warnings
|
|
framework.
|
|
|
|
|
|
.. data:: 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 :const:`version`. It is provided in the :mod:`sys`
|
|
module for informational purposes; modifying this value has no effect on the
|
|
registry keys used by Python. Availability: Windows.
|
|
|
|
|
|
.. data:: _xoptions
|
|
|
|
A dictionary of the various implementation-specific flags passed through
|
|
the :option:`-X` command-line option. Option names are either mapped to
|
|
their values, if given explicitly, or to :const:`True`. Example::
|
|
|
|
$ ./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}
|
|
|
|
.. impl-detail::
|
|
|
|
This is a CPython-specific way of accessing options passed through
|
|
:option:`-X`. Other implementations may export them through other
|
|
means, or not at all.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. rubric:: Citations
|
|
|
|
.. [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 .
|
|
|