fix: find dotenv from direct thread targets

CHANGELOG.md

@@ -9,6 +9,8 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- `load_dotenv` now finds a current-directory `.env` when called directly as a
+  `threading.Thread` target, fixing [#531] reported by [@kazzmir]
 - An unquoted empty value followed by an inline comment (e.g. `KEY= # comment`) is now parsed as an empty string instead of the comment text by [@Noethix55555] in [#663]
 
 ## [1.2.3] - 2026-08-16
@@ -431,6 +433,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [#454]: https://github.com/theskumar/python-dotenv/issues/454
 [#474]: https://github.com/theskumar/python-dotenv/issues/474
 [#523]: https://github.com/theskumar/python-dotenv/issues/523
+[#531]: https://github.com/theskumar/python-dotenv/issues/531
 [#553]: https://github.com/theskumar/python-dotenv/issues/553
 [#569]: https://github.com/theskumar/python-dotenv/issues/569
 [#583]: https://github.com/theskumar/python-dotenv/issues/583
@@ -483,6 +486,7 @@ os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
 [@jadutter]: https://github.com/jadutter
 [@jankislinger]: https://github.com/jankislinger
 [@jctanner]: https://github.com/jctanner
+[@kazzmir]: https://github.com/kazzmir
 [@larsks]: https://github.com/larsks
 [@lsmith77]: https://github.com/lsmith77
 [@matthewfranglen]: https://github.com/matthewfranglen

src/dotenv/main.py

@@ -5,6 +5,7 @@
 import stat
 import sys
 import tempfile
+import threading
 from collections import OrderedDict
 from contextlib import contextmanager
 from typing import IO, Dict, Iterable, Iterator, Mapping, Optional, Tuple, Union
@@ -372,7 +373,11 @@ def _is_debugger():
             assert frame.f_back is not None
             frame = frame.f_back
         frame_filename = frame.f_code.co_filename
-        path = os.path.dirname(os.path.abspath(frame_filename))
+        path = (
+            os.getcwd()
+            if frame.f_globals is vars(threading)
+            else os.path.dirname(os.path.abspath(frame_filename))
+        )
 
     for dirname in _walk_to_root(path):
         check_path = os.path.join(dirname, filename)

tests/test_main.py

@@ -5,6 +5,7 @@
 import subprocess
 import sys
 import textwrap
+import threading
 from unittest import mock
 
 import pytest
@@ -676,6 +677,99 @@ def test_load_dotenv_in_current_dir(tmp_path):
     assert result.stdout == "b\n"
 
 
+@mock.patch.dict(os.environ, {}, clear=True)
+def test_load_dotenv_as_thread_target(tmp_path, monkeypatch):
+    dotenv_path = tmp_path / ".env"
+    dotenv_path.write_text("a=b")
+    monkeypatch.chdir(tmp_path)
+
+    thread = threading.Thread(target=dotenv.load_dotenv)
+    thread.start()
+    thread.join()
+
+    assert not thread.is_alive()
+    assert os.environ.get("a") == "b"
+
+
+def test_find_dotenv_from_module_named_threading(tmp_path):
+    project_dir = tmp_path / "project"
+    project_dir.mkdir()
+    dotenv_path = project_dir / ".env"
+    dotenv_path.write_text("a=b")
+    module_path = project_dir / "threading.py"
+    module_path.touch()
+    elsewhere = tmp_path / "elsewhere"
+    elsewhere.mkdir()
+    runner_path = elsewhere / "runner.py"
+    runner_path.write_text(
+        textwrap.dedent(
+            f"""
+            namespace = {{"__name__": "threading"}}
+            exec(
+                compile(
+                    "from dotenv import find_dotenv\\nresult = find_dotenv()\\n",
+                    {str(module_path)!r},
+                    "exec",
+                ),
+                namespace,
+            )
+            print(namespace["result"])
+            """
+        )
+    )
+
+    result = subprocess.run(
+        [sys.executable, str(runner_path)],
+        cwd=elsewhere,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.stdout == f"{dotenv_path}\n"
+
+
+def test_load_dotenv_from_thread_wrapper_uses_wrapper_location(tmp_path):
+    project_dir = tmp_path / "project"
+    project_dir.mkdir()
+    (project_dir / ".env").write_text("a=b")
+    wrapper_path = project_dir / "wrapper.py"
+    wrapper_path.write_text(
+        "from dotenv import load_dotenv\n\ndef load():\n    load_dotenv()\n"
+    )
+    elsewhere = tmp_path / "elsewhere"
+    elsewhere.mkdir()
+    runner_path = elsewhere / "runner.py"
+    runner_path.write_text(
+        textwrap.dedent(
+            f"""
+            import os
+            import sys
+            import threading
+
+            sys.path.insert(0, {str(project_dir)!r})
+            from wrapper import load
+
+            os.environ.pop("a", None)
+            thread = threading.Thread(target=load)
+            thread.start()
+            thread.join()
+            print(os.environ["a"])
+            """
+        )
+    )
+
+    result = subprocess.run(
+        [sys.executable, str(runner_path)],
+        cwd=elsewhere,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.stdout == "b\n"
+
+
 def test_dotenv_values_file(dotenv_path):
     dotenv_path.write_text("a=b")