refactor: use importlib for dynamic imports

CHANGELOG.md

@@ -10,6 +10,9 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - [#970](https://github.com/pytask-dev/pytask/pull/970) prevents tee-sys capture from
   replaying output that was already displayed when capture stops before its buffer is
   read.
+- [#972](https://github.com/pytask-dev/pytask/pull/972) uses
+  `importlib.import_module` for dynamic imports of custom PDB classes and warning
+  categories.
 - [#968](https://github.com/pytask-dev/pytask/pull/968) improves the performance of file
   descriptor capture for tasks that produce no output.
 - Documents the pytest provenance of the adapted debugging, marker, and warning

src/_pytask/debugging.py

@@ -7,6 +7,7 @@
 from __future__ import annotations
 
 import functools
+import importlib
 import pdb  # noqa: T100
 import sys
 from typing import TYPE_CHECKING
@@ -173,8 +174,7 @@ def _import_pdb_cls(
             modname, classname = usepdb_cls
 
             try:
-                __import__(modname)
-                mod = sys.modules[modname]
+                mod = importlib.import_module(modname)
 
                 # Handle --pdbcls=pdb:pdb.Pdb (useful e.g. with pdbpp or pdbp).
                 parts = classname.split(".")

src/_pytask/warnings_utils.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import functools
+import importlib
 import re
 import textwrap
 import warnings
@@ -124,7 +125,7 @@ def _resolve_warning_category(category: str) -> type[Warning]:
         klass = category
     else:
         module, _, klass = category.rpartition(".")
-        m = __import__(module, None, None, [klass])
+        m = importlib.import_module(module)
     cat = getattr(m, klass)
     if not issubclass(cat, Warning):
         msg = f"{cat} is not a Warning subclass"

tests/test_debugging.py

@@ -1,14 +1,17 @@
 from __future__ import annotations
 
 import os
+import pdb  # noqa: T100
 import re
 import sys
 import textwrap
 from contextlib import ExitStack as does_not_raise  # noqa: N813
+from types import SimpleNamespace
 
 import click
 import pytest
 
+from _pytask.debugging import PytaskPDB
 from _pytask.debugging import _pdbcls_callback
 from pytask import ExitCode
 from pytask import cli
@@ -70,6 +73,29 @@ def task_example():
     _flush(child)
 
 
+def test_import_pdb_cls_uses_import_module(monkeypatch):
+    class CustomPdb(pdb.Pdb):
+        pass
+
+    module = SimpleNamespace(CustomPdb=CustomPdb)
+    imported = []
+
+    def import_module(name):
+        imported.append(name)
+        return module
+
+    monkeypatch.setattr("importlib.import_module", import_module)
+    monkeypatch.setattr(
+        PytaskPDB, "_config", {"pdbcls": ("package.debuggers", "CustomPdb")}
+    )
+    monkeypatch.setattr(PytaskPDB, "_wrapped_pdb_cls", None)
+
+    wrapped = PytaskPDB._import_pdb_cls(None, None)  # type: ignore[arg-type]
+
+    assert imported == ["package.debuggers"]
+    assert issubclass(wrapped, CustomPdb)
+
+
 @pytest.mark.skipif(not IS_PEXPECT_INSTALLED, reason="pexpect is not installed.")
 @pytest.mark.skipif(sys.platform == "win32", reason="pexpect cannot spawn on Windows.")
 def test_post_mortem_on_error_w_kwargs(tmp_path):

tests/test_warnings.py

@@ -2,15 +2,36 @@
 
 import sys
 import textwrap
+from types import SimpleNamespace
 
 import pytest
 
+from _pytask.warnings_utils import _resolve_warning_category
 from pytask import ExitCode
 from pytask import build
 from pytask import cli
 from tests.conftest import run_in_subprocess
 
 
+def test_resolve_warning_category_uses_import_module(monkeypatch):
+    class CustomWarning(Warning):
+        pass
+
+    module = SimpleNamespace(CustomWarning=CustomWarning)
+    imported = []
+
+    def import_module(name):
+        imported.append(name)
+        return module
+
+    monkeypatch.setattr("importlib.import_module", import_module)
+
+    result = _resolve_warning_category("package.warnings.CustomWarning")
+
+    assert imported == ["package.warnings"]
+    assert result is CustomWarning
+
+
 @pytest.mark.parametrize(
     "disable_warnings",
     [pytest.param(True, marks=pytest.mark.filterwarnings("ignore:warning!!!")), False],