Replace deprecated imp module with importlib

[hugovk]

This project uses the imp module which has been deprecated since Python 3.4 and set for removal in 3.12:

• Raised PendingDeprecationWarning since 3.4 (2014)
• Raised DeprecationWarning since 3.5 (2015)
• Updated DeprecationWarning to say removal in 3.12 since 3.10 (2021)
• Removal planned for 3.12 (2023)

Python 3.12 is set for release on 2023-10-02 and this library is one of the top 5,000 most-downloaded from PyPI.

Please could you upgrade to use importlib? The imp docs have suggestions on what to use to replace each function and constant.

[mgorny]

Ping. This is now blocking Python 3.12 support.

[mgorny]

I'm going to give it a shot.

[mgorny]

Ok, I give up. This is the closest I've been able to come up with:

diff --git a/configurations/importer.py b/configurations/importer.py
index e3573f4..00e7728 100644
--- a/configurations/importer.py
+++ b/configurations/importer.py
@@ -1,4 +1,6 @@
 import imp
+from importlib.machinery import PathFinder
+import importlib.util
 import logging
 import os
 import sys
@@ -126,25 +128,31 @@ class ConfigurationImporter:
                                                       self.name))
                 self.logger.debug(stylize(message))
 
-    def find_module(self, fullname, path=None):
+    def find_spec(self, fullname, path=None, target=None):
         if fullname is not None and fullname == self.module:
             module = fullname.rsplit('.', 1)[-1]
-            return ConfigurationLoader(self.name,
-                                       imp.find_module(module, path))
+            spec = PathFinder.find_spec(module, path, target)
+            assert spec is not None
+            return importlib.machinery.ModuleSpec(
+                spec.name,
+                ConfigurationLoader(self.name, spec),
+                origin=spec.origin)
         return None
 
 
 class ConfigurationLoader:
 
-    def __init__(self, name, location):
+    def __init__(self, name, spec):
         self.name = name
-        self.location = location
+        self.spec = spec
 
     def load_module(self, fullname):
         if fullname in sys.modules:
             mod = sys.modules[fullname]  # pragma: no cover
         else:
-            mod = imp.load_module(fullname, *self.location)
+            mod = importlib.util.module_from_spec(self.spec)
+            sys.modules[fullname] = mod
+            self.spec.loader.exec_module(mod)
         cls_path = '{0}.{1}'.format(mod.__name__, self.name)
 
         try:

However, it fails a bunch of test cases:

$ django-cadmin test
Found 70 test(s).
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
.EE............FF............./tmp/django-configurations/.tox/py311-dj42/lib/python3.11/site-packages/dj_email_url.py:89: UserWarning: `smtps` scheme will be deprecated in a future version, use `submission` instead
  warnings.warn(
........................................
======================================================================
ERROR: test_inherited (tests.test_inheritance.InheritanceTests.test_inherited)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.11/unittest/mock.py", line 1828, in _inner
    return f(*args, **kw)
           ^^^^^^^^^^^^^^
  File "/tmp/django-configurations/tests/test_inheritance.py", line 14, in test_inherited
    from tests.settings import single_inheritance
  File "/tmp/django-configurations/configurations/importer.py", line 155, in load_module
    self.spec.loader.exec_module(mod)
  File "/tmp/django-configurations/tests/settings/single_inheritance.py", line 1, in <module>
    from .base import Base
ImportError: attempted relative import with no known parent package

======================================================================
ERROR: test_inherited2 (tests.test_inheritance.InheritanceTests.test_inherited2)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.11/unittest/mock.py", line 1828, in _inner
    return f(*args, **kw)
           ^^^^^^^^^^^^^^
  File "/tmp/django-configurations/tests/test_inheritance.py", line 24, in test_inherited2
    from tests.settings import multiple_inheritance
  File "/tmp/django-configurations/configurations/importer.py", line 155, in load_module
    self.spec.loader.exec_module(mod)
  File "/tmp/django-configurations/tests/settings/multiple_inheritance.py", line 1, in <module>
    from .single_inheritance import Inheritance as BaseInheritance
ImportError: attempted relative import with no known parent package

======================================================================
FAIL: test_repr (tests.test_main.MainTests.test_repr)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/django-configurations/tests/test_main.py", line 66, in test_repr
    self.assertEqual(repr(Test),
AssertionError: "<Configuration 'main.Test'>" != "<Configuration 'tests.settings.main.Test'>"
- <Configuration 'main.Test'>
+ <Configuration 'tests.settings.main.Test'>
?                 +++++++++++++++


======================================================================
FAIL: test_simple (tests.test_main.MainTests.test_simple)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/django-configurations/tests/test_main.py", line 30, in test_simple
    self.assertRaises(AttributeError, lambda: main.POST_SETUP_TEST_SETTING)
AssertionError: AttributeError not raised by <lambda>

----------------------------------------------------------------------
Ran 70 tests in 1.249s

FAILED (failures=2, errors=2)
Destroying test database for alias 'default'...

[gump]

This has been resolved in #365