path: root/Lib/importlib/_bootstrap.py

"""Core implementation of import.

This module is NOT meant to be directly imported! It has been designed such
that it can be bootstrapped into Python as the implementation of import. As
such it requires the injection of specific modules and attributes in order to
work. One should use importlib as the public-facing version of this module.

"""

# Injected modules are '_warnings', 'imp', 'sys', 'marshal', 'errno', '_io',
# and '_os' (a.k.a. 'posix', 'nt' or 'os2').
# Injected attribute is path_sep.
#
# When editing this code be aware that code executed at import time CANNOT
# reference any injected objects! This includes not only global code but also
# anything specified at the class level.


# Bootstrap-related code ######################################################

# XXX Could also expose Modules/getpath.c:joinpath()
def _path_join(*args):
    """Replacement for os.path.join."""
    return path_sep.join(x[:-len(path_sep)] if x.endswith(path_sep) else x
                            for x in args)


def _path_exists(path):
    """Replacement for os.path.exists."""
    try:
        _os.stat(path)
    except OSError:
        return False
    else:
        return True


def _path_is_mode_type(path, mode):
    """Test whether the path is the specified mode type."""
    try:
        stat_info = _os.stat(path)
    except OSError:
        return False
    return (stat_info.st_mode & 0o170000) == mode


# XXX Could also expose Modules/getpath.c:isfile()
def _path_isfile(path):
    """Replacement for os.path.isfile."""
    return _path_is_mode_type(path, 0o100000)


# XXX Could also expose Modules/getpath.c:isdir()
def _path_isdir(path):
    """Replacement for os.path.isdir."""
    return _path_is_mode_type(path, 0o040000)


def _path_without_ext(path, ext_type):
    """Replacement for os.path.splitext()[0]."""
    for suffix in _suffix_list(ext_type):
        if path.endswith(suffix):
            return path[:-len(suffix)]
    else:
        raise ValueError("path is not of the specified type")


def _path_absolute(path):
    """Replacement for os.path.abspath."""
    if not path:
        path = _os.getcwd()
    try:
        return _os._getfullpathname(path)
    except AttributeError:
        if path.startswith('/'):
            return path
        else:
            return _path_join(_os.getcwd(), path)


class _closing:

    """Simple replacement for contextlib.closing."""

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

    def __enter__(self):
        return self.obj

    def __exit__(self, *args):
        self.obj.close()


def _wrap(new, old):
    """Simple substitute for functools.wraps."""
    for replace in ['__module__', '__name__', '__doc__']:
        setattr(new, replace, getattr(old, replace))
    new.__dict__.update(old.__dict__)


# Finder/loader utility code ##################################################

def set_package(fxn):
    """Set __package__ on the returned module."""
    def wrapper(*args, **kwargs):
        module = fxn(*args, **kwargs)
        if not hasattr(module, '__package__') or module.__package__ is None:
            module.__package__ = module.__name__
            if not hasattr(module, '__path__'):
                module.__package__ = module.__package__.rpartition('.')[0]
        return module
    _wrap(wrapper, fxn)
    return wrapper


def set_loader(fxn):
    """Set __loader__ on the returned module."""
    def wrapper(self, *args, **kwargs):
        module = fxn(self, *args, **kwargs)
        if not hasattr(module, '__loader__'):
            module.__loader__ = self
        return module
    _wrap(wrapper, fxn)
    return wrapper


def module_for_loader(fxn):
    """Decorator to handle selecting the proper module for loaders.

    The decorated function is passed the module to use instead of the module
    name. The module passed in to the function is either from sys.modules if
    it already exists or is a new module which has __name__ set and is inserted
    into sys.modules. If an exception is raised and the decorator created the
    module it is subsequently removed from sys.modules.

    The decorator assumes that the decorated function takes the module name as
    the second argument.

    """
    def decorated(self, fullname):
        module = sys.modules.get(fullname)
        is_reload = bool(module)
        if not is_reload:
            # This must be done before open() is called as the 'io' module
            # implicitly imports 'locale' and would otherwise trigger an
            # infinite loop.
            module = imp.new_module(fullname)
            sys.modules[fullname] = module
        try:
            return fxn(self, module)
        except:
            if not is_reload:
                del sys.modules[fullname]
            raise
    _wrap(decorated, fxn)
    return decorated


def _check_name(method):
    """Decorator to verify that the module being requested matches the one the
    loader can handle.

    The first argument (self) must define _name which the second argument is
    comapred against. If the comparison fails then ImportError is raised.

    """
    def inner(self, name, *args, **kwargs):
        if self._name != name:
            raise ImportError("loader cannot handle %s" % name)
        return method(self, name, *args, **kwargs)
    _wrap(inner, method)
    return inner


def _requires_builtin(fxn):
    """Decorator to verify the named module is built-in."""
    def wrapper(self, fullname):
        if fullname not in sys.builtin_module_names:
            raise ImportError("{0} is not a built-in module".format(fullname))
        return fxn(self, fullname)
    _wrap(wrapper, fxn)
    return wrapper


def _requires_frozen(fxn):
    """Decorator to verify the named module is frozen."""
    def wrapper(self, fullname):
        if not imp.is_frozen(fullname):
            raise ImportError("{0} is not a frozen module".format(fullname))
        return fxn(self, fullname)
    _wrap(wrapper, fxn)
    return wrapper


def _suffix_list(suffix_type):
    """Return a list of file suffixes based on the imp file type."""
    return [suffix[0] for suffix in imp.get_suffixes()
            if suffix[2] == suffix_type]


# Loaders #####################################################################

class BuiltinImporter:

    """Meta path import for built-in modules.

    All methods are either class or static methods to avoid the need to
    instantiate the class.

    """

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find the built-in module.

        If 'path' is ever specified then the search is considered a failure.

        """
        if path is not None:
            return None
        return cls if imp.is_builtin(fullname) else None

    @classmethod
    @set_package
    @set_loader
    @_requires_builtin
    def load_module(cls, fullname):
        """Load a built-in module."""
        is_reload = fullname in sys.modules
        try:
            return imp.init_builtin(fullname)
        except:
            if not is_reload and fullname in sys.modules:
                del sys.modules[fullname]
            raise

    @classmethod
    @_requires_builtin
    def get_code(cls, fullname):
        """Return None as built-in modules do not have code objects."""
        return None

    @classmethod
    @_requires_builtin
    def get_source(cls, fullname):
        """Return None as built-in modules do not have source code."""
        return None

    @classmethod
    @_requires_builtin
    def is_package(cls, fullname):
        """Return None as built-in module are never packages."""
        return False


class FrozenImporter:

    """Meta path import for frozen modules.

    All methods are either class or static methods to avoid the need to
    instantiate the class.

    """

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find a frozen module."""
        return cls if imp.is_frozen(fullname) else None

    @classmethod
    @set_package
    @set_loader
    @_requires_frozen
    def load_module(cls, fullname):
        """Load a frozen module."""
        is_reload = fullname in sys.modules
        try:
            return imp.init_frozen(fullname)
        except:
            if not is_reload and fullname in sys.modules:
                del sys.modules[fullname]
            raise

    @classmethod
    @_requires_frozen
    def get_code(cls, fullname):
        """Return the code object for the frozen module."""
        return imp.get_frozen_object(fullname)

    @classmethod
    @_requires_frozen
    def get_source(cls, fullname):
        """Return None as frozen modules do not have source code."""
        return None

    @classmethod
    @_requires_frozen
    def is_package(cls, fullname):
        """Return if the frozen module is a package."""
        return imp.is_frozen_package(fullname)


class PyLoader:

    """Loader base class for Python source code.

    Subclasses need to implement the methods:

    - source_path
    - get_data
    - is_package

    """

    @module_for_loader
    def load_module(self, module):
        """Initialize the module."""
        name = module.__name__
        code_object = self.get_code(module.__name__)
        module.__file__ = self.get_filename(name)
        if self.is_package(name):
            module.__path__  = [module.__file__.rsplit(path_sep, 1)[0]]
        module.__package__ = module.__name__
        if not hasattr(module, '__path__'):
            module.__package__ = module.__package__.rpartition('.')[0]
        module.__loader__ = self
        exec(code_object, module.__dict__)
        return module

    def get_filename(self, fullname):
        """Return the path to the source file, else raise ImportError."""
        path = self.source_path(fullname)
        if path is not None:
            return path
        else:
            raise ImportError("no source path available for "
                                "{0!r}".format(fullname))

    def get_code(self, fullname):
        """Get a code object from source."""
        source_path = self.source_path(fullname)
        if source_path is None:
            message = "a source path must exist to load {0}".format(fullname)
            raise ImportError(message)
        source = self.get_data(source_path)
        # Convert to universal newlines.
        line_endings = b'\n'
        for index, c in enumerate(source):
            if c == ord(b'\n'):
                break
            elif c == ord(b'\r'):
                line_endings = b'\r'
                try:
                    if source[index+1] == ord(b'\n'):
                        line_endings += b'\n'
                except IndexError:
                    pass
                break
        if line_endings != b'\n':
            source = source.replace(line_endings, b'\n')
        return compile(source, source_path, 'exec', dont_inherit=True)

    # Never use in implementing import! Imports code within the method.
    def get_source(self, fullname):
        """Return the source code for a module.

        self.source_path() and self.get_data() are used to implement this
        method.

        """
        path = self.source_path(fullname)
        if path is None:
            return None
        try:
            source_bytes = self.get_data(path)
        except IOError:
            return ImportError("source not available through get_data()")
        import io
        import tokenize
        encoding = tokenize.detect_encoding(io.BytesIO(source_bytes).readline)
        return source_bytes.decode(encoding[0])


class PyPycLoader(PyLoader):

    """Loader base class for Python source and bytecode.

    Requires implementing the methods needed for PyLoader as well as
    source_mtime, bytecode_path, and write_bytecode.

    """

    def get_filename(self, fullname):
        """Return the source or bytecode file path."""
        path = self.source_path(fullname)
        if path is not None:
            return path
        path = self.bytecode_path(fullname)
        if path is not None:
            return path
        raise ImportError("no source or bytecode path available for "
                            "{0!r}".format(fullname))

    def get_code(self, fullname):
        """Get a code object from source or bytecode."""
        # XXX Care enough to make sure this call does not happen if the magic
        #     number is bad?
        source_timestamp = self.source_mtime(fullname)
        # Try to use bytecode if it is available.
        bytecode_path = self.bytecode_path(fullname)
        if bytecode_path:
            data = self.get_data(bytecode_path)
            magic = data[:4]
            pyc_timestamp = marshal._r_long(data[4:8])
            bytecode = data[8:]
            try:
                # Verify that the magic number is valid.
                if imp.get_magic() != magic:
                    raise ImportError("bad magic number")
                # Verify that the bytecode is not stale (only matters when
                # there is source to fall back on.
                if source_timestamp:
                    if pyc_timestamp < source_timestamp:
                        raise ImportError("bytecode is stale")
            except ImportError:
                # If source is available give it a shot.
                if source_timestamp is not None:
                    pass
                else:
                    raise
            else:
                # Bytecode seems fine, so try to use it.
                # XXX If the bytecode is ill-formed, would it be beneficial to
                #     try for using source if available and issue a warning?
                return marshal.loads(bytecode)
        elif source_timestamp is None:
            raise ImportError("no source or bytecode available to create code "
                                "object for {0!r}".format(fullname))
        # Use the source.
        code_object = super().get_code(fullname)
        # Generate bytecode and write it out.
        if not sys.dont_write_bytecode:
            data = bytearray(imp.get_magic())
            data.extend(marshal._w_long(source_timestamp))
            data.extend(marshal.dumps(code_object))
            self.write_bytecode(fullname, data)
        return code_object


class _PyFileLoader(PyLoader):

    """Load a Python source file."""

    def __init__(self, name, path, is_pkg):
        self._name = name
        self._is_pkg = is_pkg
        # Figure out the base path based on whether it was source or bytecode
        # that was found.
        try:
            self._base_path = _path_without_ext(path, imp.PY_SOURCE)
        except ValueError:
            self._base_path = _path_without_ext(path, imp.PY_COMPILED)

    def _find_path(self, ext_type):
        """Find a path from the base path and the specified extension type that
        exists, returning None if one is not found."""
        for suffix in _suffix_list(ext_type):
            path = self._base_path + suffix
            if _path_exists(path):
                return path
        else:
            return None

    @_check_name
    def source_path(self, fullname):
        """Return the path to an existing source file for the module, or None
        if one cannot be found."""
        # Not a property so that it is easy to override.
        return self._find_path(imp.PY_SOURCE)

    def get_data(self, path):
        """Return the data from path as raw bytes."""
        return _io.FileIO(path, 'r').read()  # Assuming bytes.

    @_check_name
    def is_package(self, fullname):
        """Return a boolean based on whether the module is a package.

        Raises ImportError (like get_source) if the loader cannot handle the
        package.

        """
        return self._is_pkg


class _PyPycFileLoader(PyPycLoader, _PyFileLoader):

    """Load a module from a source or bytecode file."""

    @_check_name
    def source_mtime(self, name):
        """Return the modification time of the source for the specified
        module."""
        source_path = self.source_path(name)
        if not source_path:
            return None
        return int(_os.stat(source_path).st_mtime)

    @_check_name
    def bytecode_path(self, fullname):
        """Return the path to a bytecode file, or None if one does not
        exist."""
        # Not a property for easy overriding.
        return self._find_path(imp.PY_COMPILED)

    @_check_name
    def write_bytecode(self, name, data):
        """Write out 'data' for the specified module, returning a boolean
        signifying if the write-out actually occurred.

        Raises ImportError (just like get_source) if the specified module
        cannot be handled by the loader.

        """
        bytecode_path = self.bytecode_path(name)
        if not bytecode_path:
            bytecode_path = self._base_path + _suffix_list(imp.PY_COMPILED)[0]
        try:
            # Assuming bytes.
            with _closing(_io.FileIO(bytecode_path, 'w')) as bytecode_file:
                bytecode_file.write(data)
                return True
        except IOError as exc:
            if exc.errno == errno.EACCES:
                return False
            else:
                raise


class _ExtensionFileLoader:

    """Loader for extension modules.

    The constructor is designed to work with FileFinder.

    """

    def __init__(self, name, path, is_pkg):
        """Initialize the loader.

        If is_pkg is True then an exception is raised as extension modules
        cannot be the __init__ module for an extension module.

        """
        self._name = name
        self._path = path
        if is_pkg:
            raise ValueError("extension modules cannot be packages")

    @_check_name
    @set_package
    @set_loader
    def load_module(self, fullname):
        """Load an extension module."""
        is_reload = fullname in sys.modules
        try:
            return imp.load_dynamic(fullname, self._path)
        except:
            if not is_reload and fullname in sys.modules:
                del sys.modules[fullname]
            raise

    @_check_name
    def is_package(self, fullname):
        """Return False as an extension module can never be a package."""
        return False

    @_check_name
    def get_code(self, fullname):
        """Return None as an extension module cannot create a code object."""
        return None

    @_check_name
    def get_source(self, fullname):
        """Return None as extension modules have no source code."""
        return None


# Finders #####################################################################

class PathFinder:

    """Meta path finder for sys.(path|path_hooks|path_importer_cache)."""

    @classmethod
    def _path_hooks(cls, path, hooks=None):
        """Search sequence of hooks for a finder for 'path'.

        If 'hooks' is false then use sys.path_hooks.

        """
        if not hooks:
            hooks = sys.path_hooks
        for hook in hooks:
            try:
                return hook(path)
            except ImportError:
                continue
        else:
            raise ImportError("no path hook found for {0}".format(path))

    @classmethod
    def _path_importer_cache(cls, path, default=None):
        """Get the finder for the path from sys.path_importer_cache.

        If the path is not in the cache, find the appropriate finder and cache
        it. If None is cached, get the default finder and cache that
        (if applicable).

        Because of NullImporter, some finder should be returned. The only
        explicit fail case is if None is cached but the path cannot be used for
        the default hook, for which ImportError is raised.

        """
        try:
            finder = sys.path_importer_cache[path]
        except KeyError:
            finder = cls._path_hooks(path)
            sys.path_importer_cache[path] = finder
        else:
            if finder is None and default:
                # Raises ImportError on failure.
                finder = default(path)
                sys.path_importer_cache[path] = finder
        return finder

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find the module on sys.path or 'path' based on sys.path_hooks and
        sys.path_importer_cache."""
        if not path:
            path = sys.path
        for entry in path:
            try:
                finder = cls._path_importer_cache(entry)
            except ImportError:
                continue
            if finder:
                loader = finder.find_module(fullname)
                if loader:
                    return loader
        else:
            return None


class _ChainedFinder:

    """Finder that sequentially calls other finders."""

    def __init__(self, *finders):
        self._finders = finders

    def find_module(self, fullname, path=None):
        for finder in self._finders:
            result = finder.find_module(fullname, path)
            if result:
                return result
        else:
            return None


class _FileFinder:

    """Base class for file finders.

    Subclasses are expected to define the following attributes:

        * _suffixes
            Sequence of file suffixes whose order will be followed.

        * _possible_package
            True if importer should check for packages.

        * _loader
            A callable that takes the module name, a file path, and whether
            the path points to a package and returns a loader for the module
            found at that path.

    """

    def __init__(self, path_entry):
        """Initialize an importer for the passed-in sys.path entry (which is
        assumed to have already been verified as an existing directory).

        Can be used as an entry on sys.path_hook.

        """
        absolute_path = _path_absolute(path_entry)
        if not _path_isdir(absolute_path):
            raise ImportError("only directories are supported")
        self._path_entry = absolute_path

    def find_module(self, fullname, path=None):
        tail_module = fullname.rpartition('.')[2]
        package_directory = None
        if self._possible_package:
            for ext in self._suffixes:
                package_directory = _path_join(self._path_entry, tail_module)
                init_filename = '__init__' + ext
                package_init = _path_join(package_directory, init_filename)
                if (_path_isfile(package_init) and
                        _case_ok(self._path_entry, tail_module) and
                        _case_ok(package_directory, init_filename)):
                    return self._loader(fullname, package_init, True)
        for ext in self._suffixes:
            file_name = tail_module + ext
            file_path = _path_join(self._path_entry, file_name)
            if (_path_isfile(file_path) and
                    _case_ok(self._path_entry, file_name)):
                return self._loader(fullname, file_path, False)
        else:
            # Raise a warning if it matches a directory w/o an __init__ file.
            if (package_directory is not None and
                    _path_isdir(package_directory) and
                    _case_ok(self._path_entry, tail_module)):
                _warnings.warn("Not importing directory %s: missing __init__"
                                % package_directory, ImportWarning)
            return None


class _PyFileFinder(_FileFinder):

    """Importer for source/bytecode files."""

    _possible_package = True
    _loader = _PyFileLoader

    def __init__(self, path_entry):
        # Lack of imp during class creation means _suffixes is set here.
        # Make sure that Python source files are listed first!  Needed for an
        # optimization by the loader.
        self._suffixes = _suffix_list(imp.PY_SOURCE)
        super().__init__(path_entry)


class _PyPycFileFinder(_PyFileFinder):

    """Finder for source and bytecode files."""

    _loader = _PyPycFileLoader

    def __init__(self, path_entry):
        super().__init__(path_entry)
        self._suffixes += _suffix_list(imp.PY_COMPILED)




class _ExtensionFileFinder(_FileFinder):

    """Importer for extension files."""

    _possible_package = False
    _loader = _ExtensionFileLoader

    def __init__(self, path_entry):
        # Assigning to _suffixes here instead of at the class level because
        # imp is not imported at the time of class creation.
        self._suffixes = _suffix_list(imp.C_EXTENSION)
        super().__init__(path_entry)


# Import itself ###############################################################

def _chained_path_hook(*path_hooks):
    """Create a closure which sequentially checks path hooks to see which ones
    (if any) can work with a path."""
    def path_hook(entry):
        """Check to see if 'entry' matches any of the enclosed path hooks."""
        finders = []
        for hook in path_hooks:
            try:
                finder = hook(entry)
            except ImportError:
                continue
            else:
                finders.append(finder)
        if not finders:
            raise ImportError("no finder found")
        else:
            return _ChainedFinder(*finders)

    return path_hook


_DEFAULT_PATH_HOOK = _chained_path_hook(_ExtensionFileFinder, _PyPycFileFinder)

class _DefaultPathFinder(PathFinder):

    """Subclass of PathFinder that implements implicit semantics for
    __import__."""

    @classmethod
    def _path_hooks(cls, path):
        """Search sys.path_hooks as well as implicit path hooks."""
        try:
            return super()._path_hooks(path)
        except ImportError:
            implicit_hooks = [_DEFAULT_PATH_HOOK, imp.NullImporter]
            return super()._path_hooks(path, implicit_hooks)

    @classmethod
    def _path_importer_cache(cls, path):
        """Use the default path hook when None is stored in
        sys.path_importer_cache."""
        return super()._path_importer_cache(path, _DEFAULT_PATH_HOOK)


class _ImportLockContext:

    """Context manager for the import lock."""

    def __enter__(self):
        """Acquire the import lock."""
        imp.acquire_lock()

    def __exit__(self, exc_type, exc_value, exc_traceback):
        """Release the import lock regardless of any raised exceptions."""
        imp.release_lock()


_IMPLICIT_META_PATH = [BuiltinImporter, FrozenImporter, _DefaultPathFinder]

def _gcd_import(name, package=None, level=0):
    """Import and return the module based on its name, the package the call is
    being made from, and the level adjustment.

    This function represents the greatest common denominator of functionality
    between import_module and __import__. This includes settting __package__ if
    the loader did not.

    """
    if package:
        if not hasattr(package, 'rindex'):
            raise ValueError("__package__ not set to a string")
        elif package not in sys.modules:
            msg = ("Parent module {0!r} not loaded, cannot perform relative "
                   "import")
            raise SystemError(msg.format(package))
    if not name and level == 0:
        raise ValueError("Empty module name")
    if level > 0:
        dot = len(package)
        for x in range(level, 1, -1):
            try:
                dot = package.rindex('.', 0, dot)
            except ValueError:
                raise ValueError("attempted relative import beyond "
                                 "top-level package")
        if name:
            name = "{0}.{1}".format(package[:dot], name)
        else:
            name = package[:dot]
    with _ImportLockContext():
        try:
            module = sys.modules[name]
            if module is None:
                message = ("import of {} halted; "
                            "None in sys.modules".format(name))
                raise ImportError(message)
            return module
        except KeyError:
            pass
        parent = name.rpartition('.')[0]
        path = None
        if parent:
            if parent not in sys.modules:
                _gcd_import(parent)
            # Backwards-compatibility; be nicer to skip the dict lookup.
            parent_module = sys.modules[parent]
            try:
                path = parent_module.__path__
            except AttributeError:
                raise ImportError("no module named {}; "
                                    "{} is not a package".format(name, parent))
        meta_path = sys.meta_path + _IMPLICIT_META_PATH
        for finder in meta_path:
            loader = finder.find_module(name, path)
            if loader is not None:
                loader.load_module(name)
                break
        else:
            raise ImportError("No module named {0}".format(name))
        # Backwards-compatibility; be nicer to skip the dict lookup.
        module = sys.modules[name]
        if parent:
            # Set the module as an attribute on its parent.
            setattr(parent_module, name.rpartition('.')[2], module)
        # Set __package__ if the loader did not.
        if not hasattr(module, '__package__') or module.__package__ is None:
            # Watch out for what comes out of sys.modules to not be a module,
            # e.g. an int.
            try:
                module.__package__ = module.__name__
                if not hasattr(module, '__path__'):
                    module.__package__ = module.__package__.rpartition('.')[0]
            except AttributeError:
                pass
        return module


def __import__(name, globals={}, locals={}, fromlist=[], level=0):
    """Import a module.

    The 'globals' argument is used to infer where the import is occuring from
    to handle relative imports. The 'locals' argument is ignored. The
    'fromlist' argument specifies what should exist as attributes on the module
    being imported (e.g. ``from module import <fromlist>``).  The 'level'
    argument represents the package location to import from in a relative
    import (e.g. ``from ..pkg import mod`` would have a 'level' of 2).

    """
    if not hasattr(name, 'rpartition'):
        raise TypeError("module name must be str, not {}".format(type(name)))
    if level == 0:
        module = _gcd_import(name)
    else:
        # __package__ is not guaranteed to be defined or could be set to None
        # to represent that it's proper value is unknown
        package = globals.get('__package__')
        if package is None:
            package = globals['__name__']
            if '__path__' not in globals:
                package = package.rpartition('.')[0]
        module = _gcd_import(name, package, level)
    # The hell that is fromlist ...
    if not fromlist:
        # Return up to the first dot in 'name'. This is complicated by the fact
        # that 'name' may be relative.
        if level == 0:
            return sys.modules[name.partition('.')[0]]
        elif not name:
            return module
        else:
            cut_off = len(name) - len(name.partition('.')[0])
            return sys.modules[module.__name__[:-cut_off]]
    else:
        # If a package was imported, try to import stuff from fromlist.
        if hasattr(module, '__path__'):
            if '*' in fromlist and hasattr(module, '__all__'):
                fromlist = list(fromlist)
                fromlist.remove('*')
                fromlist.extend(module.__all__)
            for x in (y for y in fromlist if not hasattr(module,y)):
                try:
                    _gcd_import('{0}.{1}'.format(module.__name__, x))
                except ImportError:
                    pass
        return module