1 """

     2 Import utilities

     3 

     4 Exported classes:

     5     ImportManager   Manage the import process

     6 

     7     Importer        Base class for replacing standard import functions

     8     BuiltinImporter Emulate the import mechanism for builtin and frozen modules

     9 

    10     DynLoadSuffixImporter

    11 """

    12 from warnings import warnpy3k

    13 warnpy3k("the imputil module has been removed in Python 3.0", stacklevel=2)

    14 del warnpy3k

    15 

    16 # note: avoid importing non-builtin modules

    17 import imp                      ### not available in JPython?

    18 import sys

    19 import __builtin__

    20 

    21 # for the DirectoryImporter

    22 import struct

    23 import marshal

    24 

    25 __all__ = ["ImportManager","Importer","BuiltinImporter"]

    26 

    27 _StringType = type('')

    28 _ModuleType = type(sys)         ### doesn't work in JPython...

    29 

    30 class ImportManager:

    31     "Manage the import process."

    32 

    33     def install(self, namespace=vars(__builtin__)):

    34         "Install this ImportManager into the specified namespace."

    35 

    36         if isinstance(namespace, _ModuleType):

    37             namespace = vars(namespace)

    38 

    39         # Note: we have no notion of "chaining"

    40 

    41         # Record the previous import hook, then install our own.

    42         self.previous_importer = namespace['__import__']

    43         self.namespace = namespace

    44         namespace['__import__'] = self._import_hook

    45 

    46         ### fix this

    47         #namespace['reload'] = self._reload_hook

    48 

    49     def uninstall(self):

    50         "Restore the previous import mechanism."

    51         self.namespace['__import__'] = self.previous_importer

    52 

    53     def add_suffix(self, suffix, importFunc):

    54         assert callable(importFunc)

    55         self.fs_imp.add_suffix(suffix, importFunc)

    56 

    57     ######################################################################

    58     #

    59     # PRIVATE METHODS

    60     #

    61 

    62     clsFilesystemImporter = None

    63 

    64     def __init__(self, fs_imp=None):

    65         # we're definitely going to be importing something in the future,

    66         # so let's just load the OS-related facilities.

    67         if not _os_stat:

    68             _os_bootstrap()

    69 

    70         # This is the Importer that we use for grabbing stuff from the

    71         # filesystem. It defines one more method (import_from_dir) for our use.

    72         if fs_imp is None:

    73             cls = self.clsFilesystemImporter or _FilesystemImporter

    74             fs_imp = cls()

    75         self.fs_imp = fs_imp

    76 

    77         # Initialize the set of suffixes that we recognize and import.

    78         # The default will import dynamic-load modules first, followed by

    79         # .py files (or a .py file's cached bytecode)

    80         for desc in imp.get_suffixes():

    81             if desc[2] == imp.C_EXTENSION:

    82                 self.add_suffix(desc[0],

    83                                 DynLoadSuffixImporter(desc).import_file)

    84         self.add_suffix('.py', py_suffix_importer)

    85 

    86     def _import_hook(self, fqname, globals=None, locals=None, fromlist=None):

    87         """Python calls this hook to locate and import a module."""

    88 

    89         parts = fqname.split('.')

    90 

    91         # determine the context of this import

    92         parent = self._determine_import_context(globals)

    93 

    94         # if there is a parent, then its importer should manage this import

    95         if parent:

    96             module = parent.__importer__._do_import(parent, parts, fromlist)

    97             if module:

    98                 return module

    99 

   100         # has the top module already been imported?

   101         try:

   102             top_module = sys.modules[parts[0]]

   103         except KeyError:

   104 

   105             # look for the topmost module

   106             top_module = self._import_top_module(parts[0])

   107             if not top_module:

   108                 # the topmost module wasn't found at all.

   109                 raise ImportError, 'No module named ' + fqname

   110 

   111         # fast-path simple imports

   112         if len(parts) == 1:

   113             if not fromlist:

   114                 return top_module

   115 

   116             if not top_module.__dict__.get('__ispkg__'):

   117                 # __ispkg__ isn't defined (the module was not imported by us),

   118                 # or it is zero.

   119                 #

   120                 # In the former case, there is no way that we could import

   121                 # sub-modules that occur in the fromlist (but we can't raise an

   122                 # error because it may just be names) because we don't know how

   123                 # to deal with packages that were imported by other systems.

   124                 #

   125                 # In the latter case (__ispkg__ == 0), there can't be any sub-

   126                 # modules present, so we can just return.

   127                 #

   128                 # In both cases, since len(parts) == 1, the top_module is also

   129                 # the "bottom" which is the defined return when a fromlist

   130                 # exists.

   131                 return top_module

   132 

   133         importer = top_module.__dict__.get('__importer__')

   134         if importer:

   135             return importer._finish_import(top_module, parts[1:], fromlist)

   136 

   137         # Grrr, some people "import os.path" or do "from os.path import ..."

   138         if len(parts) == 2 and hasattr(top_module, parts[1]):

   139             if fromlist:

   140                 return getattr(top_module, parts[1])

   141             else:

   142                 return top_module

   143 

   144         # If the importer does not exist, then we have to bail. A missing

   145         # importer means that something else imported the module, and we have

   146         # no knowledge of how to get sub-modules out of the thing.

   147         raise ImportError, 'No module named ' + fqname

   148 

   149     def _determine_import_context(self, globals):

   150         """Returns the context in which a module should be imported.

   151 

   152         The context could be a loaded (package) module and the imported module

   153         will be looked for within that package. The context could also be None,

   154         meaning there is no context -- the module should be looked for as a

   155         "top-level" module.

   156         """

   157 

   158         if not globals or not globals.get('__importer__'):

   159             # globals does not refer to one of our modules or packages. That

   160             # implies there is no relative import context (as far as we are

   161             # concerned), and it should just pick it off the standard path.

   162             return None

   163 

   164         # The globals refer to a module or package of ours. It will define

   165         # the context of the new import. Get the module/package fqname.

   166         parent_fqname = globals['__name__']

   167 

   168         # if a package is performing the import, then return itself (imports

   169         # refer to pkg contents)

   170         if globals['__ispkg__']:

   171             parent = sys.modules[parent_fqname]

   172             assert globals is parent.__dict__

   173             return parent

   174 

   175         i = parent_fqname.rfind('.')

   176 

   177         # a module outside of a package has no particular import context

   178         if i == -1:

   179             return None

   180 

   181         # if a module in a package is performing the import, then return the

   182         # package (imports refer to siblings)

   183         parent_fqname = parent_fqname[:i]

   184         parent = sys.modules[parent_fqname]

   185         assert parent.__name__ == parent_fqname

   186         return parent

   187 

   188     def _import_top_module(self, name):

   189         # scan sys.path looking for a location in the filesystem that contains

   190         # the module, or an Importer object that can import the module.

   191         for item in sys.path:

   192             if isinstance(item, _StringType):

   193                 module = self.fs_imp.import_from_dir(item, name)

   194             else:

   195                 module = item.import_top(name)

   196             if module:

   197                 return module

   198         return None

   199 

   200     def _reload_hook(self, module):

   201         "Python calls this hook to reload a module."

   202 

   203         # reloading of a module may or may not be possible (depending on the

   204         # importer), but at least we can validate that it's ours to reload

   205         importer = module.__dict__.get('__importer__')

   206         if not importer:

   207             ### oops. now what...

   208             pass

   209 

   210         # okay. it is using the imputil system, and we must delegate it, but

   211         # we don't know what to do (yet)

   212         ### we should blast the module dict and do another get_code(). need to

   213         ### flesh this out and add proper docco...

   214         raise SystemError, "reload not yet implemented"

   215 

   216 

   217 class Importer:

   218     "Base class for replacing standard import functions."

   219 

   220     def import_top(self, name):

   221         "Import a top-level module."

   222         return self._import_one(None, name, name)

   223 

   224     ######################################################################

   225     #

   226     # PRIVATE METHODS

   227     #

   228     def _finish_import(self, top, parts, fromlist):

   229         # if "a.b.c" was provided, then load the ".b.c" portion down from

   230         # below the top-level module.

   231         bottom = self._load_tail(top, parts)

   232 

   233         # if the form is "import a.b.c", then return "a"

   234         if not fromlist:

   235             # no fromlist: return the top of the import tree

   236             return top

   237 

   238         # the top module was imported by self.

   239         #

   240         # this means that the bottom module was also imported by self (just

   241         # now, or in the past and we fetched it from sys.modules).

   242         #

   243         # since we imported/handled the bottom module, this means that we can

   244         # also handle its fromlist (and reliably use __ispkg__).

   245 

   246         # if the bottom node is a package, then (potentially) import some

   247         # modules.

   248         #

   249         # note: if it is not a package, then "fromlist" refers to names in

   250         #       the bottom module rather than modules.

   251         # note: for a mix of names and modules in the fromlist, we will

   252         #       import all modules and insert those into the namespace of

   253         #       the package module. Python will pick up all fromlist names

   254         #       from the bottom (package) module; some will be modules that

   255         #       we imported and stored in the namespace, others are expected

   256         #       to be present already.

   257         if bottom.__ispkg__:

   258             self._import_fromlist(bottom, fromlist)

   259 

   260         # if the form is "from a.b import c, d" then return "b"

   261         return bottom

   262 

   263     def _import_one(self, parent, modname, fqname):

   264         "Import a single module."

   265 

   266         # has the module already been imported?

   267         try:

   268             return sys.modules[fqname]

   269         except KeyError:

   270             pass

   271 

   272         # load the module's code, or fetch the module itself

   273         result = self.get_code(parent, modname, fqname)

   274         if result is None:

   275             return None

   276 

   277         module = self._process_result(result, fqname)

   278 

   279         # insert the module into its parent

   280         if parent:

   281             setattr(parent, modname, module)

   282         return module

   283 

   284     def _process_result(self, (ispkg, code, values), fqname):

   285         # did get_code() return an actual module? (rather than a code object)

   286         is_module = isinstance(code, _ModuleType)

   287 

   288         # use the returned module, or create a new one to exec code into

   289         if is_module:

   290             module = code

   291         else:

   292             module = imp.new_module(fqname)

   293 

   294         ### record packages a bit differently??

   295         module.__importer__ = self

   296         module.__ispkg__ = ispkg

   297 

   298         # insert additional values into the module (before executing the code)

   299         module.__dict__.update(values)

   300 

   301         # the module is almost ready... make it visible

   302         sys.modules[fqname] = module

   303 

   304         # execute the code within the module's namespace

   305         if not is_module:

   306             try:

   307                 exec code in module.__dict__

   308             except:

   309                 if fqname in sys.modules:

   310                     del sys.modules[fqname]

   311                 raise

   312 

   313         # fetch from sys.modules instead of returning module directly.

   314         # also make module's __name__ agree with fqname, in case

   315         # the "exec code in module.__dict__" played games on us.

   316         module = sys.modules[fqname]

   317         module.__name__ = fqname

   318         return module

   319 

   320     def _load_tail(self, m, parts):

   321         """Import the rest of the modules, down from the top-level module.

   322 

   323         Returns the last module in the dotted list of modules.

   324         """

   325         for part in parts:

   326             fqname = "%s.%s" % (m.__name__, part)

   327             m = self._import_one(m, part, fqname)

   328             if not m:

   329                 raise ImportError, "No module named " + fqname

   330         return m

   331 

   332     def _import_fromlist(self, package, fromlist):

   333         'Import any sub-modules in the "from" list.'

   334 

   335         # if '*' is present in the fromlist, then look for the '__all__'

   336         # variable to find additional items (modules) to import.

   337         if '*' in fromlist:

   338             fromlist = list(fromlist) + \

   339                        list(package.__dict__.get('__all__', []))

   340 

   341         for sub in fromlist:

   342             # if the name is already present, then don't try to import it (it

   343             # might not be a module!).

   344             if sub != '*' and not hasattr(package, sub):

   345                 subname = "%s.%s" % (package.__name__, sub)

   346                 submod = self._import_one(package, sub, subname)

   347                 if not submod:

   348                     raise ImportError, "cannot import name " + subname

   349 

   350     def _do_import(self, parent, parts, fromlist):

   351         """Attempt to import the module relative to parent.

   352 

   353         This method is used when the import context specifies that <self>

   354         imported the parent module.

   355         """

   356         top_name = parts[0]

   357         top_fqname = parent.__name__ + '.' + top_name

   358         top_module = self._import_one(parent, top_name, top_fqname)

   359         if not top_module:

   360             # this importer and parent could not find the module (relatively)

   361             return None

   362 

   363         return self._finish_import(top_module, parts[1:], fromlist)

   364 

   365     ######################################################################

   366     #

   367     # METHODS TO OVERRIDE

   368     #

   369     def get_code(self, parent, modname, fqname):

   370         """Find and retrieve the code for the given module.

   371 

   372         parent specifies a parent module to define a context for importing. It

   373         may be None, indicating no particular context for the search.

   374 

   375         modname specifies a single module (not dotted) within the parent.

   376 

   377         fqname specifies the fully-qualified module name. This is a

   378         (potentially) dotted name from the "root" of the module namespace

   379         down to the modname.

   380         If there is no parent, then modname==fqname.

   381 

   382         This method should return None, or a 3-tuple.

   383 

   384         * If the module was not found, then None should be returned.

   385 

   386         * The first item of the 2- or 3-tuple should be the integer 0 or 1,

   387             specifying whether the module that was found is a package or not.

   388 

   389         * The second item is the code object for the module (it will be

   390             executed within the new module's namespace). This item can also

   391             be a fully-loaded module object (e.g. loaded from a shared lib).

   392 

   393         * The third item is a dictionary of name/value pairs that will be

   394             inserted into new module before the code object is executed. This

   395             is provided in case the module's code expects certain values (such

   396             as where the module was found). When the second item is a module

   397             object, then these names/values will be inserted *after* the module

   398             has been loaded/initialized.

   399         """

   400         raise RuntimeError, "get_code not implemented"

   401 

   402 

   403 ######################################################################

   404 #

   405 # Some handy stuff for the Importers

   406 #

   407 

   408 # byte-compiled file suffix character

   409 _suffix_char = __debug__ and 'c' or 'o'

   410 

   411 # byte-compiled file suffix

   412 _suffix = '.py' + _suffix_char

   413 

   414 def _compile(pathname, timestamp):

   415     """Compile (and cache) a Python source file.

   416 

   417     The file specified by <pathname> is compiled to a code object and

   418     returned.

   419 

   420     Presuming the appropriate privileges exist, the bytecodes will be

   421     saved back to the filesystem for future imports. The source file's

   422     modification timestamp must be provided as a Long value.

   423     """

   424     codestring = open(pathname, 'rU').read()

   425     if codestring and codestring[-1] != '\n':

   426         codestring = codestring + '\n'

   427     code = __builtin__.compile(codestring, pathname, 'exec')

   428 

   429     # try to cache the compiled code

   430     try:

   431         f = open(pathname + _suffix_char, 'wb')

   432     except IOError:

   433         pass

   434     else:

   435         f.write('\0\0\0\0')

   436         f.write(struct.pack('<I', timestamp))

   437         marshal.dump(code, f)

   438         f.flush()

   439         f.seek(0, 0)

   440         f.write(imp.get_magic())

   441         f.close()

   442 

   443     return code

   444 

   445 _os_stat = _os_path_join = None

   446 def _os_bootstrap():

   447     "Set up 'os' module replacement functions for use during import bootstrap."

   448 

   449     names = sys.builtin_module_names

   450 

   451     join = None

   452     if 'posix' in names:

   453         sep = '/'

   454         from posix import stat

   455     elif 'nt' in names:

   456         sep = '\\'

   457         from nt import stat

   458     elif 'dos' in names:

   459         sep = '\\'

   460         from dos import stat

   461     elif 'os2' in names:

   462         sep = '\\'

   463         from os2 import stat

   464     elif 'mac' in names:

   465         from mac import stat

   466         def join(a, b):

   467             if a == '':

   468                 return b

   469             if ':' not in a:

   470                 a = ':' + a

   471             if a[-1:] != ':':

   472                 a = a + ':'

   473             return a + b

   474     else:

   475         raise ImportError, 'no os specific module found'

   476 

   477     if join is None:

   478         def join(a, b, sep=sep):

   479             if a == '':

   480                 return b

   481             lastchar = a[-1:]

   482             if lastchar == '/' or lastchar == sep:

   483                 return a + b

   484             return a + sep + b

   485 

   486     global _os_stat

   487     _os_stat = stat

   488 

   489     global _os_path_join

   490     _os_path_join = join

   491 

   492 def _os_path_isdir(pathname):

   493     "Local replacement for os.path.isdir()."

   494     try:

   495         s = _os_stat(pathname)

   496     except OSError:

   497         return None

   498     return (s.st_mode & 0170000) == 0040000

   499 

   500 def _timestamp(pathname):

   501     "Return the file modification time as a Long."

   502     try:

   503         s = _os_stat(pathname)

   504     except OSError:

   505         return None

   506     return long(s.st_mtime)

   507 

   508 

   509 ######################################################################

   510 #

   511 # Emulate the import mechanism for builtin and frozen modules

   512 #

   513 class BuiltinImporter(Importer):

   514     def get_code(self, parent, modname, fqname):

   515         if parent:

   516             # these modules definitely do not occur within a package context

   517             return None

   518 

   519         # look for the module

   520         if imp.is_builtin(modname):

   521             type = imp.C_BUILTIN

   522         elif imp.is_frozen(modname):

   523             type = imp.PY_FROZEN

   524         else:

   525             # not found

   526             return None

   527 

   528         # got it. now load and return it.

   529         module = imp.load_module(modname, None, modname, ('', '', type))

   530         return 0, module, { }

   531 

   532 

   533 ######################################################################

   534 #

   535 # Internal importer used for importing from the filesystem

   536 #

   537 class _FilesystemImporter(Importer):

   538     def __init__(self):

   539         self.suffixes = [ ]

   540 

   541     def add_suffix(self, suffix, importFunc):

   542         assert callable(importFunc)

   543         self.suffixes.append((suffix, importFunc))

   544 

   545     def import_from_dir(self, dir, fqname):

   546         result = self._import_pathname(_os_path_join(dir, fqname), fqname)

   547         if result:

   548             return self._process_result(result, fqname)

   549         return None

   550 

   551     def get_code(self, parent, modname, fqname):

   552         # This importer is never used with an empty parent. Its existence is

   553         # private to the ImportManager. The ImportManager uses the

   554         # import_from_dir() method to import top-level modules/packages.

   555         # This method is only used when we look for a module within a package.

   556         assert parent

   557 

   558         for submodule_path in parent.__path__:

   559             code = self._import_pathname(_os_path_join(submodule_path, modname), fqname)

   560             if code is not None:

   561                 return code

   562         return self._import_pathname(_os_path_join(parent.__pkgdir__, modname),

   563                                      fqname)

   564 

   565     def _import_pathname(self, pathname, fqname):

   566         if _os_path_isdir(pathname):

   567             result = self._import_pathname(_os_path_join(pathname, '__init__'),

   568                                            fqname)

   569             if result:

   570                 values = result[2]

   571                 values['__pkgdir__'] = pathname

   572                 values['__path__'] = [ pathname ]

   573                 return 1, result[1], values

   574             return None

   575 

   576         for suffix, importFunc in self.suffixes:

   577             filename = pathname + suffix

   578             try:

   579                 finfo = _os_stat(filename)

   580             except OSError:

   581                 pass

   582             else:

   583                 return importFunc(filename, finfo, fqname)

   584         return None

   585 

   586 ######################################################################

   587 #

   588 # SUFFIX-BASED IMPORTERS

   589 #

   590 

   591 def py_suffix_importer(filename, finfo, fqname):

   592     file = filename[:-3] + _suffix

   593     t_py = long(finfo[8])

   594     t_pyc = _timestamp(file)

   595 

   596     code = None

   597     if t_pyc is not None and t_pyc >= t_py:

   598         f = open(file, 'rb')

   599         if f.read(4) == imp.get_magic():

   600             t = struct.unpack('<I', f.read(4))[0]

   601             if t == t_py:

   602                 code = marshal.load(f)

   603         f.close()

   604     if code is None:

   605         file = filename

   606         code = _compile(file, t_py)

   607 

   608     return 0, code, { '__file__' : file }

   609 

   610 class DynLoadSuffixImporter:

   611     def __init__(self, desc):

   612         self.desc = desc

   613 

   614     def import_file(self, filename, finfo, fqname):

   615         fp = open(filename, self.desc[1])

   616         module = imp.load_module(fqname, fp, filename, self.desc)

   617         module.__file__ = filename

   618         return 0, module, { }

   619 

   620 

   621 ######################################################################

   622 

   623 def _print_importers():

   624     items = sys.modules.items()

   625     items.sort()

   626     for name, module in items:

   627         if module:

   628             print name, module.__dict__.get('__importer__', '-- no importer')

   629         else:

   630             print name, '-- non-existent module'

   631 

   632 def _test_revamp():

   633     ImportManager().install()

   634     sys.path.insert(0, BuiltinImporter())

   635 

   636 ######################################################################

   637 

   638 #

   639 # TODO

   640 #

   641 # from Finn Bock:

   642 #   type(sys) is not a module in JPython. what to use instead?

   643 #   imp.C_EXTENSION is not in JPython. same for get_suffixes and new_module

   644 #

   645 #   given foo.py of:

   646 #      import sys

   647 #      sys.modules['foo'] = sys

   648 #

   649 #   ---- standard import mechanism

   650 #   >>> import foo

   651 #   >>> foo

   652 #   <module 'sys' (built-in)>

   653 #

   654 #   ---- revamped import mechanism

   655 #   >>> import imputil

   656 #   >>> imputil._test_revamp()

   657 #   >>> import foo

   658 #   >>> foo

   659 #   <module 'foo' from 'foo.py'>

   660 #

   661 #

   662 # from MAL:

   663 #   should BuiltinImporter exist in sys.path or hard-wired in ImportManager?

   664 #   need __path__ processing

   665 #   performance

   666 #   move chaining to a subclass [gjs: it's been nuked]

   667 #   deinstall should be possible

   668 #   query mechanism needed: is a specific Importer installed?

   669 #   py/pyc/pyo piping hooks to filter/process these files

   670 #   wish list:

   671 #     distutils importer hooked to list of standard Internet repositories

   672 #     module->file location mapper to speed FS-based imports

   673 #     relative imports

   674 #     keep chaining so that it can play nice with other import hooks

   675 #

   676 # from Gordon:

   677 #   push MAL's mapper into sys.path[0] as a cache (hard-coded for apps)

   678 #

   679 # from Guido:

   680 #   need to change sys.* references for rexec environs

   681 #   need hook for MAL's walk-me-up import strategy, or Tim's absolute strategy

   682 #   watch out for sys.modules[...] is None

   683 #   flag to force absolute imports? (speeds _determine_import_context and

   684 #       checking for a relative module)

   685 #   insert names of archives into sys.path  (see quote below)

   686 #   note: reload does NOT blast module dict

   687 #   shift import mechanisms and policies around; provide for hooks, overrides

   688 #       (see quote below)

   689 #   add get_source stuff

   690 #   get_topcode and get_subcode

   691 #   CRLF handling in _compile

   692 #   race condition in _compile

   693 #   refactoring of os.py to deal with _os_bootstrap problem

   694 #   any special handling to do for importing a module with a SyntaxError?

   695 #       (e.g. clean up the traceback)

   696 #   implement "domain" for path-type functionality using pkg namespace

   697 #       (rather than FS-names like __path__)

   698 #   don't use the word "private"... maybe "internal"

   699 #

   700 #

   701 # Guido's comments on sys.path caching:

   702 #

   703 # We could cache this in a dictionary: the ImportManager can have a

   704 # cache dict mapping pathnames to importer objects, and a separate

   705 # method for coming up with an importer given a pathname that's not yet

   706 # in the cache.  The method should do a stat and/or look at the

   707 # extension to decide which importer class to use; you can register new

   708 # importer classes by registering a suffix or a Boolean function, plus a

   709 # class.  If you register a new importer class, the cache is zapped.

   710 # The cache is independent from sys.path (but maintained per

   711 # ImportManager instance) so that rearrangements of sys.path do the

   712 # right thing.  If a path is dropped from sys.path the corresponding

   713 # cache entry is simply no longer used.

   714 #

   715 # My/Guido's comments on factoring ImportManager and Importer:

   716 #

   717 # > However, we still have a tension occurring here:

   718 # >

   719 # > 1) implementing policy in ImportManager assists in single-point policy

   720 # >    changes for app/rexec situations

   721 # > 2) implementing policy in Importer assists in package-private policy

   722 # >    changes for normal, operating conditions

   723 # >

   724 # > I'll see if I can sort out a way to do this. Maybe the Importer class will

   725 # > implement the methods (which can be overridden to change policy) by

   726 # > delegating to ImportManager.

   727 #

   728 # Maybe also think about what kind of policies an Importer would be

   729 # likely to want to change.  I have a feeling that a lot of the code

   730 # there is actually not so much policy but a *necessity* to get things

   731 # working given the calling conventions for the __import__ hook: whether

   732 # to return the head or tail of a dotted name, or when to do the "finish

   733 # fromlist" stuff.

   734 #