Demo/imputil/importers.py

#
# importers.py
#
# Demonstration subclasses of imputil.Importer
#

# There should be consideration for the imports below if it is desirable
# to have "all" modules be imported through the imputil system.

# these are C extensions
import sys
import imp
import struct
import marshal

# these are .py modules
import imputil
import os

######################################################################

_TupleType = type(())
_StringType = type('')

######################################################################

# byte-compiled file suffic character
_suffix_char = __debug__ and 'c' or 'o'

# byte-compiled file suffix
_suffix = '.py' + _suffix_char

# the C_EXTENSION suffixes
_c_suffixes = [x for x in imp.get_suffixes() if x[2] == imp.C_EXTENSION]

def _timestamp(pathname):
    "Return the file modification time as a Long."
    try:
        s = os.stat(pathname)
    except OSError:
        return None
    return int(s[8])

def _fs_import(dir, modname, fqname):
    "Fetch a module from the filesystem."

    pathname = os.path.join(dir, modname)
    if os.path.isdir(pathname):
        values = { '__pkgdir__' : pathname, '__path__' : [ pathname ] }
        ispkg = 1
        pathname = os.path.join(pathname, '__init__')
    else:
        values = { }
        ispkg = 0

        # look for dynload modules
        for desc in _c_suffixes:
            file = pathname + desc[0]
            try:
                fp = open(file, desc[1])
            except IOError:
                pass
            else:
                module = imp.load_module(fqname, fp, file, desc)
                values['__file__'] = file
                return 0, module, values

    t_py = _timestamp(pathname + '.py')
    t_pyc = _timestamp(pathname + _suffix)
    if t_py is None and t_pyc is None:
        return None
    code = None
    if t_py is None or (t_pyc is not None and t_pyc >= t_py):
        file = pathname + _suffix
        f = open(file, 'rb')
        if f.read(4) == imp.get_magic():
            t = struct.unpack('<I', f.read(4))[0]
            if t == t_py:
                code = marshal.load(f)
        f.close()
    if code is None:
        file = pathname + '.py'
        code = _compile(file, t_py)

    values['__file__'] = file
    return ispkg, code, values

######################################################################
#
# Simple function-based importer
#
class FuncImporter(imputil.Importer):
    "Importer subclass to delegate to a function rather than method overrides."
    def __init__(self, func):
        self.func = func
    def get_code(self, parent, modname, fqname):
        return self.func(parent, modname, fqname)

def install_with(func):
    FuncImporter(func).install()


######################################################################
#
# Base class for archive-based importing
#
class PackageArchiveImporter(imputil.Importer):
    """Importer subclass to import from (file) archives.

    This Importer handles imports of the style <archive>.<subfile>, where
    <archive> can be located using a subclass-specific mechanism and the
    <subfile> is found in the archive using a subclass-specific mechanism.

    This class defines two hooks for subclasses: one to locate an archive
    (and possibly return some context for future subfile lookups), and one
    to locate subfiles.
    """

    def get_code(self, parent, modname, fqname):
        if parent:
            # the Importer._finish_import logic ensures that we handle imports
            # under the top level module (package / archive).
            assert parent.__importer__ == self

            # if a parent "package" is provided, then we are importing a
            # sub-file from the archive.
            result = self.get_subfile(parent.__archive__, modname)
            if result is None:
                return None
            if isinstance(result, _TupleType):
                assert len(result) == 2
                return (0,) + result
            return 0, result, {}

        # no parent was provided, so the archive should exist somewhere on the
        # default "path".
        archive = self.get_archive(modname)
        if archive is None:
            return None
        return 1, "", {'__archive__':archive}

    def get_archive(self, modname):
        """Get an archive of modules.

        This method should locate an archive and return a value which can be
        used by get_subfile to load modules from it. The value may be a simple
        pathname, an open file, or a complex object that caches information
        for future imports.

        Return None if the archive was not found.
        """
        raise RuntimeError("get_archive not implemented")

    def get_subfile(self, archive, modname):
        """Get code from a subfile in the specified archive.

        Given the specified archive (as returned by get_archive()), locate
        and return a code object for the specified module name.

        A 2-tuple may be returned, consisting of a code object and a dict
        of name/values to place into the target module.

        Return None if the subfile was not found.
        """
        raise RuntimeError("get_subfile not implemented")


class PackageArchive(PackageArchiveImporter):
    "PackageArchiveImporter subclass that refers to a specific archive."

    def __init__(self, modname, archive_pathname):
        self.__modname = modname
        self.__path = archive_pathname

    def get_archive(self, modname):
        if modname == self.__modname:
            return self.__path
        return None

    # get_subfile is passed the full pathname of the archive


######################################################################
#
# Emulate the standard directory-based import mechanism
#
class DirectoryImporter(imputil.Importer):
    "Importer subclass to emulate the standard importer."

    def __init__(self, dir):
        self.dir = dir

    def get_code(self, parent, modname, fqname):
        if parent:
            dir = parent.__pkgdir__
        else:
            dir = self.dir

        # Return the module (and other info) if found in the specified
        # directory. Otherwise, return None.
        return _fs_import(dir, modname, fqname)

    def __repr__(self):
        return '<%s.%s for "%s" at 0x%x>' % (self.__class__.__module__,
                                             self.__class__.__name__,
                                             self.dir,
                                             id(self))


######################################################################
#
# Emulate the standard path-style import mechanism
#
class PathImporter(imputil.Importer):
    def __init__(self, path=sys.path):
        self.path = path

    def get_code(self, parent, modname, fqname):
        if parent:
            # we are looking for a module inside of a specific package
            return _fs_import(parent.__pkgdir__, modname, fqname)

        # scan sys.path, looking for the requested module
        for dir in self.path:
            if isinstance(dir, _StringType):
                result = _fs_import(dir, modname, fqname)
                if result:
                    return result

        # not found
        return None

######################################################################

def _test_dir():
    "Debug/test function to create DirectoryImporters from sys.path."
    imputil.ImportManager().install()
    path = sys.path[:]
    path.reverse()
    for d in path:
        sys.path.insert(0, DirectoryImporter(d))
    sys.path.insert(0, imputil.BuiltinImporter())

def _test_revamp():
    "Debug/test function for the revamped import system."
    imputil.ImportManager().install()
    sys.path.insert(0, PathImporter())
    sys.path.insert(0, imputil.BuiltinImporter())