Lib/runpy.py

   1 """runpy.py - locating and running Python code using the module namespace
   2
   3 Provides support for locating and running Python scripts using the Python
   4 module namespace instead of the native filesystem.
   5
   6 This allows Python code to play nicely with non-filesystem based PEP 302
   7 importers when locating support scripts as well as when importing modules.
   8 """
   9 # Written by Nick Coghlan <ncoghlan at gmail.com>
  10 #    to implement PEP 338 (Executing Modules as Scripts)
  11
  12 import sys
  13 import imp
  14 from pkgutil import read_code
  15 try:
  16     from imp import get_loader
  17 except ImportError:
  18     from pkgutil import get_loader
  19
  20 __all__ = [
  21     "run_module", "run_path",
  22 ]
  23
  24 class _TempModule(object):
  25     """Temporarily replace a module in sys.modules with an empty namespace"""
  26     def __init__(self, mod_name):
  27         self.mod_name = mod_name
  28         self.module = imp.new_module(mod_name)
  29         self._saved_module = []
  30
  31     def __enter__(self):
  32         mod_name = self.mod_name
  33         try:
  34             self._saved_module.append(sys.modules[mod_name])
  35         except KeyError:
  36             pass
  37         sys.modules[mod_name] = self.module
  38         return self
  39
  40     def __exit__(self, *args):
  41         if self._saved_module:
  42             sys.modules[self.mod_name] = self._saved_module[0]
  43         else:
  44             del sys.modules[self.mod_name]
  45         self._saved_module = []
  46
  47 class _ModifiedArgv0(object):
  48     def __init__(self, value):
  49         self.value = value
  50         self._saved_value = self._sentinel = object()
  51
  52     def __enter__(self):
  53         if self._saved_value is not self._sentinel:
  54             raise RuntimeError("Already preserving saved value")
  55         self._saved_value = sys.argv[0]
  56         sys.argv[0] = self.value
  57
  58     def __exit__(self, *args):
  59         self.value = self._sentinel
  60         sys.argv[0] = self._saved_value
  61
  62 def _run_code(code, run_globals, init_globals=None,
  63               mod_name=None, mod_fname=None,
  64               mod_loader=None, pkg_name=None):
  65     """Helper to run code in nominated namespace"""
  66     if init_globals is not None:
  67         run_globals.update(init_globals)
  68     run_globals.update(__name__ = mod_name,
  69                        __file__ = mod_fname,
  70                        __loader__ = mod_loader,
  71                        __package__ = pkg_name)
  72     exec code in run_globals
  73     return run_globals
  74
  75 def _run_module_code(code, init_globals=None,
  76                     mod_name=None, mod_fname=None,
  77                     mod_loader=None, pkg_name=None):
  78     """Helper to run code in new namespace with sys modified"""
  79     with _TempModule(mod_name) as temp_module, _ModifiedArgv0(mod_fname):
  80         mod_globals = temp_module.module.__dict__
  81         _run_code(code, mod_globals, init_globals,
  82                   mod_name, mod_fname, mod_loader, pkg_name)
  83     # Copy the globals of the temporary module, as they
  84     # may be cleared when the temporary module goes away
  85     return mod_globals.copy()
  86
  87
  88 # This helper is needed due to a missing component in the PEP 302
  89 # loader protocol (specifically, "get_filename" is non-standard)
  90 # Since we can't introduce new features in maintenance releases,
  91 # support was added to zipimporter under the name '_get_filename'
  92 def _get_filename(loader, mod_name):
  93     for attr in ("get_filename", "_get_filename"):
  94         meth = getattr(loader, attr, None)
  95         if meth is not None:
  96             return meth(mod_name)
  97     return None
  98
  99 # Helper to get the loader, code and filename for a module
 100 def _get_module_details(mod_name):
 101     loader = get_loader(mod_name)
 102     if loader is None:
 103         raise ImportError("No module named %s" % mod_name)
 104     if loader.is_package(mod_name):
 105         if mod_name == "__main__" or mod_name.endswith(".__main__"):
 106             raise ImportError("Cannot use package as __main__ module")
 107         try:
 108             pkg_main_name = mod_name + ".__main__"
 109             return _get_module_details(pkg_main_name)
 110         except ImportError, e:
 111             raise ImportError(("%s; %r is a package and cannot " +
 112                                "be directly executed") %(e, mod_name))
 113     code = loader.get_code(mod_name)
 114     if code is None:
 115         raise ImportError("No code object available for %s" % mod_name)
 116     filename = _get_filename(loader, mod_name)
 117     return mod_name, loader, code, filename
 118
 119
 120 def _get_main_module_details():
 121     # Helper that gives a nicer error message when attempting to
 122     # execute a zipfile or directory by invoking __main__.py
 123     main_name = "__main__"
 124     try:
 125         return _get_module_details(main_name)
 126     except ImportError as exc:
 127         if main_name in str(exc):
 128             raise ImportError("can't find %r module in %r" %
 129                               (main_name, sys.path[0]))
 130         raise
 131
 132 # This function is the actual implementation of the -m switch and direct
 133 # execution of zipfiles and directories and is deliberately kept private.
 134 # This avoids a repeat of the situation where run_module() no longer met the
 135 # needs of mainmodule.c, but couldn't be changed because it was public
 136 def _run_module_as_main(mod_name, alter_argv=True):
 137     """Runs the designated module in the __main__ namespace
 138
 139        Note that the executed module will have full access to the
 140        __main__ namespace. If this is not desirable, the run_module()
 141        function should be used to run the module code in a fresh namespace.
 142
 143        At the very least, these variables in __main__ will be overwritten:
 144            __name__
 145            __file__
 146            __loader__
 147            __package__
 148     """
 149     try:
 150         if alter_argv or mod_name != "__main__": # i.e. -m switch
 151             mod_name, loader, code, fname = _get_module_details(mod_name)
 152         else:          # i.e. directory or zipfile execution
 153             mod_name, loader, code, fname = _get_main_module_details()
 154     except ImportError as exc:
 155         msg = "%s: %s" % (sys.executable, str(exc))
 156         sys.exit(msg)
 157     pkg_name = mod_name.rpartition('.')[0]
 158     main_globals = sys.modules["__main__"].__dict__
 159     if alter_argv:
 160         sys.argv[0] = fname
 161     return _run_code(code, main_globals, None,
 162                      "__main__", fname, loader, pkg_name)
 163
 164 def run_module(mod_name, init_globals=None,
 165                run_name=None, alter_sys=False):
 166     """Execute a module's code without importing it
 167
 168        Returns the resulting top level namespace dictionary
 169     """
 170     mod_name, loader, code, fname = _get_module_details(mod_name)
 171     if run_name is None:
 172         run_name = mod_name
 173     pkg_name = mod_name.rpartition('.')[0]
 174     if alter_sys:
 175         return _run_module_code(code, init_globals, run_name,
 176                                 fname, loader, pkg_name)
 177     else:
 178         # Leave the sys module alone
 179         return _run_code(code, {}, init_globals, run_name,
 180                          fname, loader, pkg_name)
 181
 182
 183 # XXX (ncoghlan): Perhaps expose the C API function
 184 # as imp.get_importer instead of reimplementing it in Python?
 185 def _get_importer(path_name):
 186     """Python version of PyImport_GetImporter C API function"""
 187     cache = sys.path_importer_cache
 188     try:
 189         importer = cache[path_name]
 190     except KeyError:
 191         # Not yet cached. Flag as using the
 192         # standard machinery until we finish
 193         # checking the hooks
 194         cache[path_name] = None
 195         for hook in sys.path_hooks:
 196             try:
 197                 importer = hook(path_name)
 198                 break
 199             except ImportError:
 200                 pass
 201         else:
 202             # The following check looks a bit odd. The trick is that
 203             # NullImporter throws ImportError if the supplied path is a
 204             # *valid* directory entry (and hence able to be handled
 205             # by the standard import machinery)
 206             try:
 207                 importer = imp.NullImporter(path_name)
 208             except ImportError:
 209                 return None
 210         cache[path_name] = importer
 211     return importer
 212
 213 def _get_code_from_file(fname):
 214     # Check for a compiled file first
 215     with open(fname, "rb") as f:
 216         code = read_code(f)
 217     if code is None:
 218         # That didn't work, so try it as normal source code
 219         with open(fname, "rU") as f:
 220             code = compile(f.read(), fname, 'exec')
 221     return code
 222
 223 def run_path(path_name, init_globals=None, run_name=None):
 224     """Execute code located at the specified filesystem location
 225
 226        Returns the resulting top level namespace dictionary
 227
 228        The file path may refer directly to a Python script (i.e.
 229        one that could be directly executed with execfile) or else
 230        it may refer to a zipfile or directory containing a top
 231        level __main__.py script.
 232     """
 233     if run_name is None:
 234         run_name = "<run_path>"
 235     importer = _get_importer(path_name)
 236     if isinstance(importer, imp.NullImporter):
 237         # Not a valid sys.path entry, so run the code directly
 238         # execfile() doesn't help as we want to allow compiled files
 239         code = _get_code_from_file(path_name)
 240         return _run_module_code(code, init_globals, run_name, path_name)
 241     else:
 242         # Importer is defined for path, so add it to
 243         # the start of sys.path
 244         sys.path.insert(0, path_name)
 245         try:
 246             # Here's where things are a little different from the run_module
 247             # case. There, we only had to replace the module in sys while the
 248             # code was running and doing so was somewhat optional. Here, we
 249             # have no choice and we have to remove it even while we read the
 250             # code. If we don't do this, a __loader__ attribute in the
 251             # existing __main__ module may prevent location of the new module.
 252             main_name = "__main__"
 253             saved_main = sys.modules[main_name]
 254             del sys.modules[main_name]
 255             try:
 256                 mod_name, loader, code, fname = _get_main_module_details()
 257             finally:
 258                 sys.modules[main_name] = saved_main
 259             pkg_name = ""
 260             with _TempModule(run_name) as temp_module, \
 261                  _ModifiedArgv0(path_name):
 262                 mod_globals = temp_module.module.__dict__
 263                 return _run_code(code, mod_globals, init_globals,
 264                                     run_name, fname, loader, pkg_name)
 265         finally:
 266             try:
 267                 sys.path.remove(path_name)
 268             except ValueError:
 269                 pass
 270
 271
 272 if __name__ == "__main__":
 273     # Run the module specified as the next command line argument
 274     if len(sys.argv) < 2:
 275         print >> sys.stderr, "No module specified for execution"
 276     else:
 277         del sys.argv[0] # Make the requested module sys.argv[0]
 278         _run_module_as_main(sys.argv[0])