cpython/Lib/importlib/util.py

"""Utility code for constructing importers, etc."""

from ._bootstrap import MAGIC_NUMBER
from ._bootstrap import cache_from_source
from ._bootstrap import decode_source
from ._bootstrap import source_from_cache
from ._bootstrap import spec_from_loader
from ._bootstrap import spec_from_file_location
from ._bootstrap import _resolve_name

from contextlib import contextmanager
import functools
import sys
import warnings


def resolve_name(name, package):
    """Resolve a relative module name to an absolute one."""
    if not name.startswith('.'):
        return name
    elif not package:
        raise ValueError('{!r} is not a relative name '
                         '(no leading dot)'.format(name))
    level = 0
    for character in name:
        if character != '.':
            break
        level += 1
    return _resolve_name(name[level:], package, level)


@contextmanager
def _module_to_load(name):
    is_reload = name in sys.modules

    module = sys.modules.get(name)
    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 = type(sys)(name)
        # This must be done before putting the module in sys.modules
        # (otherwise an optimization shortcut in import.c becomes wrong)
        module.__initializing__ = True
        sys.modules[name] = module
    try:
        yield module
    except Exception:
        if not is_reload:
            try:
                del sys.modules[name]
            except KeyError:
                pass
    finally:
        module.__initializing__ = False


# XXX deprecate
def set_package(fxn):
    """Set __package__ on the returned module."""
    @functools.wraps(fxn)
    def set_package_wrapper(*args, **kwargs):
        module = fxn(*args, **kwargs)
        if getattr(module, '__package__', None) is None:
            module.__package__ = module.__name__
            if not hasattr(module, '__path__'):
                module.__package__ = module.__package__.rpartition('.')[0]
        return module
    return set_package_wrapper


# XXX deprecate
def set_loader(fxn):
    """Set __loader__ on the returned module."""
    @functools.wraps(fxn)
    def set_loader_wrapper(self, *args, **kwargs):
        module = fxn(self, *args, **kwargs)
        if getattr(module, '__loader__', None) is None:
            module.__loader__ = self
        return module
    return set_loader_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. If the module is new, then __name__
    is set the first argument to the method, __loader__ is set to self, and
    __package__ is set accordingly (if self.is_package() is defined) will be set
    before it is passed to the decorated function (if self.is_package() does
    not work for the module it will be set post-load).

    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.

    """
    warnings.warn('The import system now takes care of this automatically.',
                  PendingDeprecationWarning, stacklevel=2)
    @functools.wraps(fxn)
    def module_for_loader_wrapper(self, fullname, *args, **kwargs):
        with _module_to_load(fullname) as module:
            module.__loader__ = self
            try:
                is_package = self.is_package(fullname)
            except (ImportError, AttributeError):
                pass
            else:
                if is_package:
                    module.__package__ = fullname
                else:
                    module.__package__ = fullname.rpartition('.')[0]
            # If __package__ was not set above, __import__() will do it later.
            return fxn(self, module, *args, **kwargs)

    return module_for_loader_wrapper