Add support for loading a package spec on Python 2

Author: jaraco

importlib_resources/_compat.py

@@ -21,3 +21,16 @@ class ABC(object):                                          # type: ignore
     FileNotFoundError = FileNotFoundError                       # type: ignore
 except NameError:
     FileNotFoundError = OSError
+
+
+class PackageSpec(object):
+	def __init__(self, **kwargs):
+		vars(self).update(kwargs)
+
+
+def package_spec(package):
+	return getattr(package, '__spec__', None) or \
+		PackageSpec(
+			origin=package.__file__,
+			loader=getattr(package, '__loader__', None),
+		)

importlib_resources/trees.py

@@ -3,7 +3,7 @@
 import abc
 import zipp
 
-from ._compat import ABC, Path
+from ._compat import ABC, Path, package_spec
 
 
 class Traversable(ABC):
@@ -40,9 +40,10 @@ def is_file(self):
 
 def from_package(package):
     """Return a Traversable object for the given package"""
-    package_directory = Path(package.__spec__.origin).parent
+    spec = package_spec(package)
+    package_directory = Path(spec.origin).parent
     try:
-        archive_path = package.__spec__.loader.archive
+        archive_path = spec.loader.archive
         rel_path = package_directory.relative_to(archive_path)
         return zipp.Path(archive_path, str(rel_path) + '/')
     except Exception: