"runpy" --- Locating and executing Python modules
*************************************************

**Source code:** Lib/runpy.py

======================================================================

The "runpy" module is used to locate and run Python modules without
importing them first. Its main use is to implement the "-m" command
line switch that allows scripts to be located using the Python module
namespace rather than the filesystem.

Note that this is *not* a sandbox module - all code is executed in the
current process, and any side effects (such as cached imports of other
modules) will remain in place after the functions have returned.

Furthermore, any functions and classes defined by the executed code
are not guaranteed to work correctly after a "runpy" function has
returned. If that limitation is not acceptable for a given use case,
"importlib" is likely to be a more suitable choice than this module.

The "runpy" module provides two functions:

runpy.run_module(mod_name, init_globals=None, run_name=None, alter_sys=False)

   Execute the code of the specified module and return the resulting
   module globals dictionary. The module's code is first located using
   the standard import mechanism (refer to **PEP 302** for details)
   and then executed in a fresh module namespace.

   The *mod_name* argument should be an absolute module name. If the
   module name refers to a package rather than a normal module, then
   that package is imported and the "__main__" submodule within that
   package is then executed and the resulting module globals
   dictionary returned.

   The optional dictionary argument *init_globals* may be used to pre-
   populate the module's globals dictionary before the code is
   executed. The supplied dictionary will not be modified. If any of
   the special global variables below are defined in the supplied
   dictionary, those definitions are overridden by "run_module()".

   The special global variables "__name__", "__spec__", "__file__",
   "__cached__", "__loader__" and "__package__" are set in the globals
   dictionary before the module code is executed (Note that this is a
   minimal set of variables - other variables may be set implicitly as
   an interpreter implementation detail).

   "__name__" is set to *run_name* if this optional argument is not
   "None", to "mod_name + '.__main__'" if the named module is a
   package and to the *mod_name* argument otherwise.

   "__spec__" will be set appropriately for the *actually* imported
   module (that is, "__spec__.name" will always be *mod_name* or
   "mod_name + '.__main__", never *run_name*).

   "__file__", "__cached__", "__loader__" and "__package__" are set as
   normal based on the module spec.

   If the argument *alter_sys* is supplied and evaluates to "True",
   then "sys.argv[0]" is updated with the value of "__file__" and
   "sys.modules[__name__]" is updated with a temporary module object
   for the module being executed. Both "sys.argv[0]" and
   "sys.modules[__name__]" are restored to their original values
   before the function returns.

   Note that this manipulation of "sys" is not thread-safe. Other
   threads may see the partially initialised module, as well as the
   altered list of arguments. It is recommended that the "sys" module
   be left alone when invoking this function from threaded code.

   参见: The "-m" option offering equivalent functionality from the
     command line.

   在 3.1 版更改: Added ability to execute packages by looking for a
   "__main__" submodule.

   在 3.2 版更改: Added "__cached__" global variable (see **PEP
   3147**).

   在 3.4 版更改: Updated to take advantage of the module spec feature
   added by **PEP 451**. This allows "__cached__" to be set correctly
   for modules run this way, as well as ensuring the real module name
   is always accessible as "__spec__.name".

runpy.run_path(file_path, init_globals=None, run_name=None)

   Execute the code at the named filesystem location and return the
   resulting module globals dictionary. As with a script name supplied
   to the CPython command line, the supplied path may refer to a
   Python source file, a compiled bytecode file or a valid sys.path
   entry containing a "__main__" module (e.g. a zipfile containing a
   top-level "__main__.py" file).

   For a simple script, the specified code is simply executed in a
   fresh module namespace. For a valid sys.path entry (typically a
   zipfile or directory), the entry is first added to the beginning of
   "sys.path". The function then looks for and executes a "__main__"
   module using the updated path. Note that there is no special
   protection against invoking an existing "__main__" entry located
   elsewhere on "sys.path" if there is no such module at the specified
   location.

   The optional dictionary argument *init_globals* may be used to pre-
   populate the module's globals dictionary before the code is
   executed. The supplied dictionary will not be modified. If any of
   the special global variables below are defined in the supplied
   dictionary, those definitions are overridden by "run_path()".

   The special global variables "__name__", "__spec__", "__file__",
   "__cached__", "__loader__" and "__package__" are set in the globals
   dictionary before the module code is executed (Note that this is a
   minimal set of variables - other variables may be set implicitly as
   an interpreter implementation detail).

   "__name__" is set to *run_name* if this optional argument is not
   "None" and to "'<run_path>'" otherwise.

   If the supplied path directly references a script file (whether as
   source or as precompiled byte code), then "__file__" will be set to
   the supplied path, and "__spec__", "__cached__", "__loader__" and
   "__package__" will all be set to "None".

   If the supplied path is a reference to a valid sys.path entry, then
   "__spec__" will be set appropriately for the imported "__main__"
   module (that is, "__spec__.name" will always be "__main__").
   "__file__", "__cached__", "__loader__" and "__package__" will be
   set as normal based on the module spec.

   A number of alterations are also made to the "sys" module. Firstly,
   "sys.path" may be altered as described above. "sys.argv[0]" is
   updated with the value of "file_path" and "sys.modules[__name__]"
   is updated with a temporary module object for the module being
   executed. All modifications to items in "sys" are reverted before
   the function returns.

   Note that, unlike "run_module()", the alterations made to "sys" are
   not optional in this function as these adjustments are essential to
   allowing the execution of sys.path entries. As the thread-safety
   limitations still apply, use of this function in threaded code
   should be either serialised with the import lock or delegated to a
   separate process.

   参见: 接口选项 for equivalent functionality on the command line
     ("python path/to/script").

   3.2 新版功能.

   在 3.4 版更改: Updated to take advantage of the module spec feature
   added by **PEP 451**. This allows "__cached__" to be set correctly
   in the case where "__main__" is imported from a valid sys.path
   entry rather than being executed directly.

参见:

  **PEP 338** -- 将模块作为脚本执行
     PEP 由 Nick Coghlan 撰写并实现。

  **PEP 366** -- Main module explicit relative imports
     PEP 由 Nick Coghlan 撰写并实现。

  **PEP 451** -- A ModuleSpec Type for the Import System
     PEP written and implemented by Eric Snow

  命令行与环境 - CPython command line details

  The "importlib.import_module()" function
