Allow a package to resolve its own resources without having to pass a…

… reference to itself. Fixes #259.

importlib_resources/_common.py

@@ -5,21 +5,24 @@
 import contextlib
 import types
 import importlib
+import inspect
 
-from typing import Union, Optional
+from typing import Union, Optional, Dict
 from .abc import ResourceReader, Traversable
 
 from ._compat import wrap_spec
 
 Package = Union[types.ModuleType, str]
-Anchor = Package
+Anchor = Union[Package, None]
+ModuleContext = Dict[str, str]
 
 
 def files(package: Anchor) -> Traversable:
     """
     Get a Traversable resource for an anchor.
     """
-    return from_package(resolve(package))
+    context = inspect.currentframe().f_back.f_globals  # type: ignore
+    return from_package(resolve(package, context))
 
 
 def get_resource_reader(package: types.ModuleType) -> Optional[ResourceReader]:
@@ -39,15 +42,20 @@ def get_resource_reader(package: types.ModuleType) -> Optional[ResourceReader]:
 
 
 @functools.singledispatch
-def resolve(cand: Package):
+def resolve(cand: Package, context: ModuleContext):
     return cand
 
 
 @resolve.register
-def _(cand: str):
+def _(cand: str, context: ModuleContext):
     return importlib.import_module(cand)
 
 
+@resolve.register
+def _(cand: None, context: ModuleContext):
+    return resolve(context['__name__'], context)
+
+
 def from_package(package):
     """
     Return a Traversable object for the given package.