"""runpy.py - locating and running Python code using the module namespace

Provides support for locating and running Python scripts using the Python

module namespace instead of the native filesystem.

This allows Python code to play nicely with non-filesystem based PEP 302

importers when locating support scripts as well as when importing modules.

"""

# Written by Nick Coghlan <ncoghlan at gmail.com>

#    to implement PEP 338 (Executing Modules as Scripts)

import sys

import imp

try:

    from imp import get_loader

except ImportError:

    from pkgutil import get_loader

__all__ = [

    "run_module",

]

def _run_code(code, run_globals, init_globals,

              mod_name, mod_fname, mod_loader):

    """Helper for _run_module_code"""

    if init_globals is not None:

        run_globals.update(init_globals)

    run_globals.update(__name__ = mod_name,

                       __file__ = mod_fname,

                       __loader__ = mod_loader)

    exec code in run_globals

    return run_globals

def _run_module_code(code, init_globals=None,

                    mod_name=None, mod_fname=None,

                    mod_loader=None, alter_sys=False):

    """Helper for run_module"""

    # Set up the top level namespace dictionary

    if alter_sys:

        # Modify sys.argv[0] and sys.module[mod_name]

        temp_module = imp.new_module(mod_name)

        mod_globals = temp_module.__dict__

        saved_argv0 = sys.argv[0]

        restore_module = mod_name in sys.modules

        if restore_module:

            saved_module = sys.modules[mod_name]

        sys.argv[0] = mod_fname

        sys.modules[mod_name] = temp_module

        try:

            _run_code(code, mod_globals, init_globals,

                      mod_name, mod_fname, mod_loader)

        finally:

            sys.argv[0] = saved_argv0

        if restore_module:

            sys.modules[mod_name] = saved_module

        else:

            del sys.modules[mod_name]

        # Copy the globals of the temporary module, as they

        # may be cleared when the temporary module goes away

        return mod_globals.copy()

    else:

        # Leave the sys module alone

        return _run_code(code, {}, init_globals,

                         mod_name, mod_fname, mod_loader)

# This helper is needed due to a missing component in the PEP 302

# loader protocol (specifically, "get_filename" is non-standard)

def _get_filename(loader, mod_name):

    try:

        get_filename = loader.get_filename

    except AttributeError:

        return None

    else:

        return get_filename(mod_name)

def run_module(mod_name, init_globals=None,

                         run_name=None, alter_sys=False):

    """Execute a module's code without importing it

       Returns the resulting top level namespace dictionary

    """

    loader = get_loader(mod_name)

    if loader is None:

        raise ImportError("No module named " + mod_name)

    code = loader.get_code(mod_name)

    if code is None:

        raise ImportError("No code object available for " + mod_name)

    filename = _get_filename(loader, mod_name)

    if run_name is None:

        run_name = mod_name

    return _run_module_code(code, init_globals, run_name,

                            filename, loader, alter_sys)

if __name__ == "__main__":

    # Run the module specified as the next command line argument

    if len(sys.argv) < 2:

        print >> sys.stderr, "No module specified for execution"

    else:

        del sys.argv[0] # Make the requested module sys.argv[0]

        run_module(sys.argv[0], run_name="__main__", alter_sys=True)