Allow a package to resolve its own resources simply

CHANGES.rst

@@ -10,6 +10,10 @@ v5.10.0
   files was renamed from 'package' to 'anchor', with a
   compatibility shim for those passing by keyword.
 
+* #259: ``files`` no longer requires the anchor to be
+  specified and can infer the anchor from the caller's scope
+  (defaults to the caller's module).
+
 v5.9.0
 ======
 

importlib_resources/_common.py

@@ -5,7 +5,9 @@
 import contextlib
 import types
 import importlib
+import inspect
 import warnings
+import itertools
 
 from typing import Union, Optional, cast
 from .abc import ResourceReader, Traversable
@@ -22,12 +24,9 @@ def package_to_anchor(func):
 
     Other errors should fall through.
 
-    >>> files()
-    Traceback (most recent call last):
-    TypeError: files() missing 1 required positional argument: 'anchor'
     >>> files('a', 'b')
     Traceback (most recent call last):
-    TypeError: files() takes 1 positional argument but 2 were given
+    TypeError: files() takes from 0 to 1 positional arguments but 2 were given
     """
     undefined = object()
 
@@ -50,7 +49,7 @@ def wrapper(anchor=undefined, package=undefined):
 
 
 @package_to_anchor
-def files(anchor: Anchor) -> Traversable:
+def files(anchor: Optional[Anchor] = None) -> Traversable:
     """
     Get a Traversable resource for an anchor.
     """
@@ -74,7 +73,7 @@ def get_resource_reader(package: types.ModuleType) -> Optional[ResourceReader]:
 
 
 @functools.singledispatch
-def resolve(cand: Anchor) -> types.ModuleType:
+def resolve(cand: Optional[Anchor]) -> types.ModuleType:
     return cast(types.ModuleType, cand)
 
 
@@ -83,6 +82,28 @@ def _(cand: str) -> types.ModuleType:
     return importlib.import_module(cand)
 
 
+@resolve.register
+def _(cand: None) -> types.ModuleType:
+    return resolve(_infer_caller().f_globals['__name__'])
+
+
+def _infer_caller():
+    """
+    Walk the stack and find the frame of the first caller not in this module.
+    """
+
+    def is_this_file(frame_info):
+        return frame_info.filename == __file__
+
+    def is_wrapper(frame_info):
+        return frame_info.function == 'wrapper'
+
+    not_this_file = itertools.filterfalse(is_this_file, inspect.stack())
+    # also exclude 'wrapper' due to singledispatch in the call stack
+    callers = itertools.filterfalse(is_wrapper, not_this_file)
+    return next(callers).frame
+
+
 def from_package(package: types.ModuleType):
     """
     Return a Traversable object for the given package.

importlib_resources/tests/test_files.py

@@ -1,6 +1,8 @@
 import typing
+import textwrap
 import unittest
 import warnings
+import importlib
 import contextlib
 
 import importlib_resources as resources
@@ -61,14 +63,16 @@ def setUp(self):
         self.data = namespacedata01
 
 
-class ModulesFilesTests(unittest.TestCase):
+class SiteDir:
     def setUp(self):
         self.fixtures = contextlib.ExitStack()
         self.addCleanup(self.fixtures.close)
         self.site_dir = self.fixtures.enter_context(os_helper.temp_dir())
         self.fixtures.enter_context(import_helper.DirsOnSysPath(self.site_dir))
         self.fixtures.enter_context(import_helper.CleanImport())
 
+
+class ModulesFilesTests(SiteDir, unittest.TestCase):
     def test_module_resources(self):
         """
         A module can have resources found adjacent to the module.
@@ -84,5 +88,25 @@ def test_module_resources(self):
         assert actual == spec['res.txt']
 
 
+class ImplicitContextFilesTests(SiteDir, unittest.TestCase):
+    def test_implicit_files(self):
+        """
+        Without any parameter, files() will infer the location as the caller.
+        """
+        spec = {
+            'somepkg': {
+                '__init__.py': textwrap.dedent(
+                    """
+                    import importlib_resources as res
+                    val = res.files().joinpath('res.txt').read_text()
+                    """
+                ),
+                'res.txt': 'resources are the best',
+            },
+        }
+        _path.build(spec, self.site_dir)
+        assert importlib.import_module('somepkg').val == 'resources are the best'
+
+
 if __name__ == '__main__':
     unittest.main()