| :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:: 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. |
| |
| .. versionadded:: 2.0 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.5 |
| |
| |
| .. 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 ``__builtin__._``. |
| |
| ``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``. |
| |
| |
| .. 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 :option:`-B` command line option and the |
| :envvar:`PYTHONDONTWRITEBYTECODE` environment variable, but you can set it |
| yourself to control bytecode file generation. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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 |
| or having executed an except clause." For any stack frame, only information |
| about the most recently handled exception 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 exception type of the exception |
| being handled (a class object); *value* gets the exception parameter (its |
| :dfn:`associated value` or the second argument to :keyword:`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 :func:`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 |
| :keyword:`try` ... :keyword:`finally` statement) or to call :func:`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. |
| |
| |
| .. function:: exc_clear() |
| |
| This function clears all information relating to the current or last exception |
| that occurred in the current thread. After calling this function, |
| :func:`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. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. data:: exc_type |
| exc_value |
| exc_traceback |
| |
| .. deprecated:: 1.5 |
| Use :func:`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. |
| |
| |
| .. 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 |
| :file:`{exec_prefix}/lib/python{X.Y}/config`, and shared library modules are |
| installed in :file:`{exec_prefix}/lib/python{X.Y}/lib-dynload`, where *X.Y* |
| is the version number of Python, for example ``2.7``. |
| |
| |
| .. data:: executable |
| |
| A string giving the absolute path of the executable binary for the Python |
| interpreter, on systems where this makes sense. If Python is unable to retrieve |
| the real path to its executable, :data:`sys.executable` will be an empty string |
| or ``None``. |
| |
| |
| .. 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:: 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 :mod:`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. |
| |
| .. deprecated:: 2.4 |
| Use :mod:`atexit` instead. |
| |
| |
| .. data:: flags |
| |
| The struct sequence *flags* exposes the status of command line flags. The |
| attributes are read only. |
| |
| ============================= =================================== |
| attribute flag |
| ============================= =================================== |
| :const:`debug` :option:`-d` |
| :const:`py3k_warning` :option:`-3` |
| :const:`division_warning` :option:`-Q` |
| :const:`division_new` :option:`-Qnew <-Q>` |
| :const:`inspect` :option:`-i` |
| :const:`interactive` :option:`-i` |
| :const:`optimize` :option:`-O` or :option:`-OO` |
| :const:`dont_write_bytecode` :option:`-B` |
| :const:`no_user_site` :option:`-s` |
| :const:`no_site` :option:`-S` |
| :const:`ignore_environment` :option:`-E` |
| :const:`tabcheck` :option:`-t` or :option:`-tt <-t>` |
| :const:`verbose` :option:`-v` |
| :const:`unicode` :option:`-U` |
| :const:`bytes_warning` :option:`-b` |
| :const:`hash_randomization` :option:`-R` |
| ============================= =================================== |
| |
| .. versionadded:: 2.6 |
| |
| .. versionadded:: 2.7.3 |
| The ``hash_randomization`` attribute. |
| |
| .. 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. |
| |
| .. tabularcolumns:: |l|l|L| |
| |
| +---------------------+----------------+--------------------------------------------------+ |
| | 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 | 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. | |
| +---------------------+----------------+--------------------------------------------------+ |
| |
| 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' |
| |
| .. versionadded:: 2.6 |
| |
| .. 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 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. |
| |
| .. versionadded:: 2.7 |
| |
| |
| .. function:: getcheckinterval() |
| |
| Return the interpreter's "check interval"; see :func:`setcheckinterval`. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. function:: getdefaultencoding() |
| |
| Return the name of the current default string encoding used by the Unicode |
| implementation. |
| |
| .. versionadded:: 2.0 |
| |
| |
| .. 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:`dl` and :mod:`DLFCN` modules. |
| Availability: Unix. |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: 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: |
| |
| * 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. :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'``. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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`. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.3 |
| .. versionchanged:: 2.7 |
| Changed to a named tuple and added *service_pack_minor*, |
| *service_pack_major*, *suite_mask*, and *product_type*. |
| |
| |
| .. 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. |
| |
| The ``hexversion`` is a 32-bit number with the following layout: |
| |
| +-------------------------+------------------------------------------------+ |
| | Bits (big endian order) | Meaning | |
| +=========================+================================================+ |
| | :const:`1-8` | ``PY_MAJOR_VERSION`` (the ``2`` in | |
| | | ``2.1.0a3``) | |
| +-------------------------+------------------------------------------------+ |
| | :const:`9-16` | ``PY_MINOR_VERSION`` (the ``1`` in | |
| | | ``2.1.0a3``) | |
| +-------------------------+------------------------------------------------+ |
| | :const:`17-24` | ``PY_MICRO_VERSION`` (the ``0`` in | |
| | | ``2.1.0a3``) | |
| +-------------------------+------------------------------------------------+ |
| | :const:`25-28` | ``PY_RELEASE_LEVEL`` (``0xA`` for alpha, | |
| | | ``0xB`` for beta, ``0xC`` for release | |
| | | candidate and ``0xF`` for final) | |
| +-------------------------+------------------------------------------------+ |
| | :const:`29-32` | ``PY_RELEASE_SERIAL`` (the ``3`` in | |
| | | ``2.1.0a3``, zero for final releases) | |
| +-------------------------+------------------------------------------------+ |
| |
| Thus ``2.1.0a3`` is hexversion ``0x020100a3``. |
| |
| .. versionadded:: 1.5.2 |
| |
| |
| .. data:: long_info |
| |
| A struct sequence that holds information about Python's |
| internal representation of integers. The attributes are read only. |
| |
| .. tabularcolumns:: |l|L| |
| |
| +-------------------------+----------------------------------------------+ |
| | Attribute | Explanation | |
| +=========================+==============================================+ |
| | :const:`bits_per_digit` | number of bits held in each digit. Python | |
| | | integers are stored internally in base | |
| | | ``2**long_info.bits_per_digit`` | |
| +-------------------------+----------------------------------------------+ |
| | :const:`sizeof_digit` | size in bytes of the C type used to | |
| | | represent a digit | |
| +-------------------------+----------------------------------------------+ |
| |
| .. versionadded:: 2.7 |
| |
| |
| .. 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 chapter :ref:`debugger` for |
| more information.) |
| |
| The meaning of the variables is the same as that of the return values from |
| :func:`exc_info` above. (Since there is only one interactive thread, |
| thread-safety is not a concern for these variables, unlike for ``exc_type`` |
| etc.) |
| |
| |
| .. data:: 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. |
| |
| .. data:: 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. |
| |
| .. 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 ``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 |
| |
| .. index:: builtin: reload |
| |
| 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 |
| :func:`reload` on the corresponding module object. |
| |
| |
| .. 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. |
| |
| .. versionchanged:: 2.3 |
| Unicode strings are no longer ignored. |
| |
| .. 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 ``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 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... |
| |
| .. versionchanged:: 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. |
| |
| For other systems, the values are: |
| |
| ===================== =========================== |
| System :data:`platform` value |
| ===================== =========================== |
| 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'`` |
| ===================== =========================== |
| |
| .. seealso:: |
| :attr:`os.name` has a coarser granularity. :func:`os.uname` gives |
| system-dependent version information. |
| |
| The :mod:`platform` module provides detailed checks for the |
| system's identity. |
| |
| .. 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 :file:`{prefix}/lib/python{X.Y}` |
| while the platform independent header files (all except :file:`pyconfig.h`) are |
| stored in :file:`{prefix}/include/python{X.Y}`, where *X.Y* is the version |
| number of Python, for example ``2.7``. |
| |
| |
| .. 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:: 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.) |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. 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. |
| |
| |
| .. function:: setdefaultencoding(name) |
| |
| Set the current default string encoding used by the Unicode implementation. If |
| *name* does not match any available encoding, :exc:`LookupError` is raised. |
| This function is only intended to be used by the :mod:`site` module |
| implementation and, where needed, by :mod:`sitecustomize`. Once used by the |
| :mod:`site` module, it is removed from the :mod:`sys` module's namespace. |
| |
| .. Note that :mod:`site` is not imported if the :option:`-S` option is passed |
| to the interpreter, in which case this function will remain available. |
| |
| .. versionadded:: 2.0 |
| |
| |
| .. 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(dl.RTLD_NOW | dl.RTLD_GLOBAL)``. Symbolic names for the |
| flag modules can be either found in the :mod:`dl` 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. |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. 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:: 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. |
| |
| .. versionadded:: 2.4 |
| |
| .. impl-detail:: |
| |
| This function is intimately bound to CPython implementation details and |
| thus not likely to be implemented elsewhere. |
| |
| |
| .. data:: stdin |
| stdout |
| stderr |
| |
| .. index:: |
| builtin: input |
| builtin: raw_input |
| |
| 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 :func:`input` and :func:`raw_input`. ``stdout`` is used for |
| the output of :keyword:`print` and :term:`expression` statements and for the |
| prompts of :func:`input` and :func:`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 :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.) |
| |
| |
| .. 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. |
| |
| |
| .. 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``. |
| |
| .. versionadded:: 2.5 |
| |
| .. note:: |
| Python is now `developed <https://docs.python.org/devguide/>`_ using |
| Mercurial. In recent Python 2.7 bugfix releases, :data:`subversion` |
| therefore contains placeholder information. It is removed in Python |
| 3.3. |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. 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. |
| |
| .. versionadded:: 2.0 |
| .. versionchanged:: 2.7 |
| 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. |
| |
| .. 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\ . |
| |
