sys.modules), and creates the fundamental modules __builtin__, __main__ and sys. It also initializes the module search path (
sys.path). It does not set
sys.argv; use PySys_SetArgv() for that. This is a no-op when called for a second time (without calling Py_Finalize() first). There is no return value; it is a fatal error if the initialization fails.
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 extensions may not work properly if their initialization routine is called more than once; this can happen if an application 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.argvvariable. It has new standard I/O stream file objects
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 in 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_Initialize(); in that case,
initmodule function is called
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 os.close() they can (accidentally or maliciously) affect each other's open files. Because of the way extensions are shared between (sub-)interpreters, some extensions may not work properly; this is especially likely when the extension makes use of (static) global variables, or when the extension manipulates its module's dictionary after its initialization. It is possible to insert objects created in one sub-interpreter into a namespace of another sub-interpreter; this should be done with great care to avoid sharing user-defined functions, methods, instances or classes between sub-interpreters, since import operations executed by such objects may affect the wrong (sub-)interpreter's dictionary of loaded modules. (XXX This is a hard-to-fix bug that will be addressed in a future release.)
Also note that the use of this functionality is incompatible with extension modules such as PyObjC and ctypes that use the PyGILState_* APIs (and this is inherent in the way the PyGILState_* functions work). Simple things may work, but confusing behavior will always be near.
argvargument to the main() function of the program. This is used by Py_GetPath() and some other functions below to find the Python run-time libraries relative to the interpreter executable. The default value is
'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.path, which may be modified to change the future search path for loaded modules.
"1.5 (#67, Dec 31 1997, 22:34:28) [GCC 220.127.116.11]"
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
'sunos5'. On Mac OS X, it is
'darwin'. 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
'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'
"#67, Aug 1 1997, 22:34:28"
|int argc, char **argv)|
sys.argvbased on argc and argv. These parameters are similar to those passed to the program's main() function with the difference that the first entry should refer to the script file to be executed rather than the executable hosting the Python interpreter. If there isn't a script that will be run, the first entry in argv can be an empty string. If this function fails to initialize
sys.argv, a fatal condition is signalled using Py_FatalError().