First phase of refactoring for runpy, pkgutil, pydoc, and setuptools

to share common PEP 302 support code, as described here:

http://mail.python.org/pipermail/python-dev/2006-April/063724.html

This revision strips all the PEP 302 emulation code from runpy,
replacing it with published API classes and functions in pkgutil,
mostly using setuptools' implementation of common functionality,
but adding features from runpy, and doing some refactoring to make
the layer pydoc needs easier to implement on top of this.

One step down, four to go, although step #4 (adding C versions of
the new APIs to 'imp') may not be able to make it in time for
alpha 2.  We'll see how that goes.

Lib/pkgutil.py

 """Utilities to support packages."""
 
+# NOTE: This module must remain compatible with Python 2.3, as it is shared
+# by setuptools for distribution with Python 2.3 and up.
+
 import os
 import sys
+import imp
+import os.path
+from types import ModuleType
+
+__all__ = [
+    'get_importer', 'iter_importers', 'get_loader', 'find_loader',
+    'ImpImporter', 'ImpLoader', 'read_code', 'extend_path',
+]
+
+def read_code(stream):
+    # This helper is needed in order for the PEP 302 emulation to
+    # correctly handle compiled files
+    import marshal
+
+    magic = stream.read(4)
+    if magic != imp.get_magic():
+        return None
+
+    stream.read(4) # Skip timestamp
+    return marshal.load(stream)
+
+
+class ImpImporter:
+    """PEP 302 Importer that wraps Python's "classic" import algorithm
+
+    ImpImporter(dirname) produces a PEP 302 importer that searches that
+    directory.  ImpImporter(None) produces a PEP 302 importer that searches
+    the current sys.path, plus any modules that are frozen or built-in.
+
+    Note that ImpImporter does not currently support being used by placement
+    on sys.meta_path.
+    """
+
+    def __init__(self, path=None):
+        self.path = path
+
+    def find_module(self, fullname, path=None):
+        # Note: we ignore 'path' argument since it is only used via meta_path
+        subname = fullname.split(".")[-1]
+        if subname != fullname and self.path is None:
+            return None
+        if self.path is None:
+            path = None
+        else:
+            path = [self.path]
+        try:
+            file, filename, etc = imp.find_module(subname, path)
+        except ImportError:
+            return None
+        return ImpLoader(fullname, file, filename, etc)
+
+
+class ImpLoader:
+    """PEP 302 Loader that wraps Python's "classic" import algorithm
+    """
+    code = source = None
+
+    def __init__(self, fullname, file, filename, etc):
+        self.file = file
+        self.filename = filename
+        self.fullname = fullname
+        self.etc = etc
+
+    def load_module(self, fullname):
+        self._reopen()
+        try:
+            mod = imp.load_module(fullname, self.file, self.filename, self.etc)
+        finally:
+            if self.file:
+                self.file.close()
+        # Note: we don't set __loader__ because we want the module to look
+        # normal; i.e. this is just a wrapper for standard import machinery
+        return mod
+
+    def get_data(self, pathname):
+        return open(pathname, "rb").read()
+
+    def _reopen(self):
+        if self.file and self.file.closed:
+            if mod_type==imp.PY_SOURCE:
+                self.file = open(self.filename, 'rU')
+            elif mod_type in (imp.PY_COMPILED, imp.C_EXTENSION):
+                self.file = open(self.filename, 'rb')
+
+    def _fix_name(self, fullname):
+        if fullname is None:
+            fullname = self.fullname
+        elif fullname != self.fullname:
+            raise ImportError("Loader for module %s cannot handle "
+                              "module %s" % (self.fullname, fullname))
+        return fullname
+
+    def is_package(self):
+        return self.etc[2]==imp.PKG_DIRECTORY
+
+    def get_code(self, fullname=None):
+        fullname = self._fix_name(fullname)
+        if self.code is None:
+            mod_type = self.etc[2]
+            if mod_type==imp.PY_SOURCE:
+                source = self.get_source(fullname)
+                self.code = compile(source, self.filename, 'exec')
+            elif mod_type==imp.PY_COMPILED:
+                self._reopen()
+                try:
+                    self.code = read_code(self.file)
+                finally:
+                    self.file.close()
+            elif mod_type==imp.PKG_DIRECTORY:
+                self.code = self._get_delegate().get_code()
+        return self.code
+
+    def get_source(self, fullname=None):
+        fullname = self._fix_name(fullname)
+        if self.source is None:
+            mod_type = self.etc[2]
+            if mod_type==imp.PY_SOURCE:
+                self._reopen()
+                try:
+                    self.source = self.file.read()
+                finally:
+                    self.file.close()
+            elif mod_type==imp.PY_COMPILED:
+                if os.path.exists(self.filename[:-1]):
+                    f = open(self.filename[:-1], 'rU')
+                    self.source = f.read()
+                    f.close()
+            elif mod_type==imp.PKG_DIRECTORY:
+                self.source = self._get_delegate().get_source()
+        return self.source
+
+    def _get_delegate(self):
+        return ImpImporter(self.filename).find_module('__init__')
+
+    def get_filename(self, fullname=None):
+        fullname = self._fix_name(fullname)
+        mod_type = self.etc[2]
+        if self.etc[2]==imp.PKG_DIRECTORY:
+            return self._get_delegate().get_filename()
+        elif self.etc[2] in (imp.PY_SOURCE, imp.PY_COMPILED, imp.C_EXTENSION):
+            return self.filename
+        return None
+
+
+def get_importer(path_item):
+    """Retrieve a PEP 302 importer for the given path item
+
+    The returned importer is cached in sys.path_importer_cache
+    if it was newly created by a path hook.
+
+    If there is no importer, a wrapper around the basic import
+    machinery is returned. This wrapper is never inserted into
+    the importer cache (None is inserted instead).
+
+    The cache (or part of it) can be cleared manually if a
+    rescan of sys.path_hooks is necessary.
+    """
+    try:
+        importer = sys.path_importer_cache[path_item]
+    except KeyError:
+        for path_hook in sys.path_hooks:
+            try:
+                importer = path_hook(path_item)
+                break
+            except ImportError:
+                pass
+        else:
+            importer = None
+        sys.path_importer_cache.setdefault(path_item,importer)
+
+    if importer is None:
+        try:
+            importer = ImpImporter(path_item)
+        except ImportError:
+            pass
+    return importer
+
+
+def iter_importers(fullname):
+    """Yield PEP 302 importers for the given module name
+
+    If fullname contains a '.', the importers will be for the package
+    containing fullname, otherwise they will be importers for sys.meta_path,
+    sys.path, and Python's "classic" import machinery, in that order.  If
+    the named module is in a package, that package is imported as a side
+    effect of invoking this function.
+
+    Non PEP 302 mechanisms (e.g. the Windows registry) used by the
+    standard import machinery to find files in alternative locations
+    are partially supported, but are searched AFTER sys.path. Normally,
+    these locations are searched BEFORE sys.path, preventing sys.path
+    entries from shadowing them.
+
+    For this to cause a visible difference in behaviour, there must
+    be a module or package name that is accessible via both sys.path
+    and one of the non PEP 302 file system mechanisms. In this case,
+    the emulation will find the former version, while the builtin
+    import mechanism will find the latter.
+
+    Items of the following types can be affected by this discrepancy:
+        imp.C_EXTENSION, imp.PY_SOURCE, imp.PY_COMPILED, imp.PKG_DIRECTORY
+    """
+    if fullname.startswith('.'):
+        raise ImportError("Relative module names not supported")
+    if '.' in fullname:
+        # Get the containing package's __path__
+        pkg = '.'.join(fullname.split('.')[:-1])
+        if pkg not in sys.modules:
+            __import__(pkg)
+        path = getattr(sys.modules[pkg],'__path__',None) or []
+    else:
+        for importer in sys.meta_path:
+            yield importer
+        path = sys.path
+    for item in path:
+        yield get_importer(item)
+    if '.' not in fullname:
+        yield ImpImporter()
+
+
+def get_loader(module_or_name):
+    """Get a PEP 302 "loader" object for module_or_name
+
+    If the module or package is accessible via the normal import
+    mechanism, a wrapper around the relevant part of that machinery
+    is returned.  Returns None if the module cannot be found or imported.
+    If the named module is not already imported, its containing package
+    (if any) is imported, in order to establish the package __path__.
+
+    This function uses iter_importers(), and is thus subject to the same
+    limitations regarding platform-specific special import locations such
+    as the Windows registry.
+    """
+    if module_or_name in sys.modules:
+        module_or_name = sys.modules[module_or_name]
+    if isinstance(module_or_name, ModuleType):
+        module = module_or_name
+        loader = getattr(module,'__loader__',None)
+        if loader is not None:
+            return loader
+        fullname = module.__name__
+    else:
+        fullname = module_or_name
+    return find_loader(fullname)
+
+
+def find_loader(fullname):
+    """Find a PEP 302 "loader" object for fullname
+
+    If fullname contains dots, path must be the containing package's __path__.
+    Returns None if the module cannot be found or imported. This function uses
+    iter_importers(), and is thus subject to the same limitations regarding
+    platform-specific special import locations such as the Windows registry.
+    """
+    for importer in iter_importers(fullname):
+        loader = importer.find_module(fullname)
+        if loader is not None:
+            return loader
+
+    return None
+
 
 def extend_path(path, name):
     """Extend a package's path.