Add initial implementation of importlib. See the NOTES files for what is

planned for the package.

There are no docs yet, but they are coming once the API for the first new
function, importlib.import_module() is finalized.

Lib/importlib/test/test_api.py

@@ -0,0 +1,62 @@
+import unittest
+import importlib
+from . import support
+
+
+class ImportModuleTests(unittest.TestCase):
+
+    """Test importlib.import_module."""
+
+    def test_module_import(self):
+        # Test importing a top-level module.
+        with support.mock_modules('top_level') as mock:
+            with support.import_state(meta_path=[mock]):
+                module = importlib.import_module('top_level')
+                self.assertEqual(module.__name__, 'top_level')
+
+    def test_absolute_package_import(self):
+        # Test importing a module from a package with an absolute name.
+        pkg_name = 'pkg'
+        pkg_long_name = '{0}.__init__'.format(pkg_name)
+        name = '{0}.mod'.format(pkg_name)
+        with support.mock_modules(pkg_long_name, name) as mock:
+            with support.import_state(meta_path=[mock]):
+                module = importlib.import_module(name)
+                self.assertEqual(module.__name__, name)
+
+    def test_relative_package_import(self):
+        # Test importing a module from a package through a relatve import.
+        pkg_name = 'pkg'
+        pkg_long_name = '{0}.__init__'.format(pkg_name)
+        module_name = 'mod'
+        absolute_name = '{0}.{1}'.format(pkg_name, module_name)
+        relative_name = '.{0}'.format(module_name)
+        with support.mock_modules(pkg_long_name, absolute_name) as mock:
+            with support.import_state(meta_path=[mock]):
+                module = importlib.import_module(relative_name, pkg_name)
+                self.assertEqual(module.__name__, absolute_name)
+
+    def test_absolute_import_with_package(self):
+        # Test importing a module from a package with an absolute name with
+        # the 'package' argument given.
+        pkg_name = 'pkg'
+        pkg_long_name = '{0}.__init__'.format(pkg_name)
+        name = '{0}.mod'.format(pkg_name)
+        with support.mock_modules(pkg_long_name, name) as mock:
+            with support.import_state(meta_path=[mock]):
+                module = importlib.import_module(name, pkg_name)
+                self.assertEqual(module.__name__, name)
+
+    def test_relative_import_wo_package(self):
+        # Relative imports cannot happen without the 'package' argument being
+        # set.
+        self.assertRaises(TypeError, importlib.import_module, '.support')
+
+
+def test_main():
+    from test.support import run_unittest
+    run_unittest(ImportModuleTests)
+
+
+if __name__ == '__main__':
+    test_main()