sys.modules
), and
sys.path
).
It does not set sys.argv
; use
PySys_SetArgv()
This function is provided for a number of reasons. An embedding application might want to restart Python without having to restart the application itself. An application that has loaded the Python interpreter from a dynamically loadable library (or DLL) might want to free all memory allocated by Python before unloading the DLL. During a hunt for memory leaks in an application a developer might want to free all memory allocated by Python before exiting from the application.
Bugs and caveats: The destruction of modules and objects in modules is done in random order; this may cause destructors (__del__() methods) to fail when they depend on other objects (even functions) or modules. Dynamically loaded extension modules loaded by Python are not unloaded. Small amounts of memory allocated by the Python interpreter may not be freed (if you find a leak, please report it). Memory tied up in circular references between objects is not freed. Some memory allocated by extension modules may not be freed. Some extension may not work properly if their initialization routine is called more than once; this can happen if an applcation calls Py_Initialize() and Py_Finalize() more than once.
sys.modules
) and the module search path (sys.path
) are
also separate. The new environment has no sys.argv
variable.
It has new standard I/O stream file objects sys.stdin
,
sys.stdout
and sys.stderr
(however these refer to the
same underlying FILE structures in the C library).
The return value points to the first thread state created in the new sub-interpreter. This thread state is made the current thread state. Note that no actual thread is created; see the discussion of thread states below. If creation of the new interpreter is unsuccessful, NULL is returned; no exception is set since the exception state is stored in the current thread state and there may not be a current thread state. (Like all other Python/C API functions, the global interpreter lock must be held before calling this function and is still held when it returns; however, unlike most other Python/C API functions, there needn't be a current thread state on entry.)
Extension modules are shared between (sub-)interpreters as follows:
the first time a particular extension is imported, it is initialized
normally, and a (shallow) copy of its module's dictionary is
squirreled away. When the same extension is imported by another
(sub-)interpreter, a new module is initialized and filled with the
contents of this copy; the extension's init
function is not
called. Note that this is different from what happens when an
extension is imported after the interpreter has been completely
re-initialized by calling
Py_Finalize()initmodule
function is called
again.
Bugs and caveats: Because sub-interpreters (and the main
interpreter) are part of the same process, the insulation between them
isn't perfect -- for example, using low-level file operations like
argv[0]
argument to the
main()"python"
. The
argument should point to a zero-terminated character string in static
storage whose contents will not change for the duration of the
program's execution. No code in the Python interpreter will change
the contents of this storage.
"/usr/local/bin/python"
,
the prefix is "/usr/local"
. The returned string points into
static storage; the caller should not modify its value. This
corresponds to the prefix variable in the top-level
Makefile and the --prefix argument to the
configure script at build time. The value is available to
Python code as sys.prefix
. It is only useful on Unix. See
also the next function.
"/usr/local/bin/python"
, the exec-prefix is
"/usr/local"
. The returned string points into static storage;
the caller should not modify its value. This corresponds to the
exec_prefix variable in the top-level Makefile and the
--exec_prefix argument to the
configure script at build time. The value is available to
Python code as sys.exec_prefix
. It is only useful on Unix.
Background: The exec-prefix differs from the prefix when platform
dependent files (such as executables and shared libraries) are
installed in a different directory tree. In a typical installation,
platform dependent files may be installed in the
"/usr/local/plat"
subtree while platform independent may be
installed in "/usr/local"
.
Generally speaking, a platform is a combination of hardware and software families, e.g. Sparc machines running the Solaris 2.x operating system are considered the same platform, but Intel machines running Solaris 2.x are another platform, and Intel machines running Linux are yet another platform. Different major revisions of the same operating system generally also form different platforms. Non-Unix operating systems are a different story; the installation strategies on those systems are so different that the prefix and exec-prefix are meaningless, and set to the empty string. Note that compiled Python bytecode files are platform independent (but not independent from the Python version by which they were compiled!).
System administrators will know how to configure the mount or
automount programs to share "/usr/local"
between platforms
while having "/usr/local/plat"
be a different filesystem for each
platform.
sys.executable
.
sys.path
"1.5 (#67, Dec 31 1997, 22:34:28) [GCC 2.7.2.2]"
The first word (up to the first space character) is the current Python
version; the first three characters are the major and minor version
separated by a period. The returned string points into static storage;
the caller should not modify its value. The value is available to
Python code as the list sys.version
.
"sunos5"
. On Macintosh, it is "mac"
. On Windows, it
is "win"
. The returned string points into static storage;
the caller should not modify its value. The value is available to
Python code as sys.platform
.
"Copyright (c) 1995-2000 Corporation for National Research Initiatives.\n\ All Rights Reserved.\n\ Copyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam.\n\ All Rights Reserved."
The returned string points into static storage; the caller should not
modify its value. The value is available to Python code as the list
sys.copyright
.
"[GCC 2.7.2.2]"
The returned string points into static storage; the caller should not
modify its value. The value is available to Python code as part of
the variable sys.version
.
"#67, Aug 1 1997, 22:34:28"
The returned string points into static storage; the caller should not
modify its value. The value is available to Python code as part of
the variable sys.version
.
sys.argv
based on argc and argv. These
parameters are similar to those passed to the program's
main()sys.argv
, a fatal
condition is signalled using
Py_FatalError()