From bf41adf2ffcbbc30bd6ed051f161b242a34daf6f Mon Sep 17 00:00:00 2001
From: Paul Ganssle <1377457+pganssle@users.noreply.github.com>
Date: Fri, 10 Mar 2023 10:29:37 -0500
Subject: [PATCH] GH-102537: Handle check for PYTHONTZPATH failing in zoneinfo
 test (GH-102538)

It is possible but unlikely for the `python_tzpath_context` function to fail between the start of the `try` block and the point where `os.environ.get` succeeds, in which case `old_env` will be undefined. In this case, we want to take no action.

Practically speaking this will really only happen in an error condition anyway, so it doesn't really matter, but we should probably do it right anyway.
(cherry picked from commit 64bde502cf89963bc7382b03ea9e1c0967d22e35)

Co-authored-by: Paul Ganssle <1377457+pganssle@users.noreply.github.com>
---
 Lib/test/test_zoneinfo/test_zoneinfo.py                  | 9 ++++++++-
 .../Tests/2023-03-08-13-54-20.gh-issue-102537.Vfplpb.rst | 2 ++
 2 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Tests/2023-03-08-13-54-20.gh-issue-102537.Vfplpb.rst

diff --git a/Lib/test/test_zoneinfo/test_zoneinfo.py b/Lib/test/test_zoneinfo/test_zoneinfo.py
index a2172f3ac21d08..fc19247b262e01 100644
--- a/Lib/test/test_zoneinfo/test_zoneinfo.py
+++ b/Lib/test/test_zoneinfo/test_zoneinfo.py
@@ -1530,13 +1530,20 @@ class TzPathTest(TzPathUserMixin, ZoneInfoTestBase):
     @contextlib.contextmanager
     def python_tzpath_context(value):
         path_var = "PYTHONTZPATH"
+        unset_env_sentinel = object()
+        old_env = unset_env_sentinel
         try:
             with OS_ENV_LOCK:
                 old_env = os.environ.get(path_var, None)
                 os.environ[path_var] = value
                 yield
         finally:
-            if old_env is None:
+            if old_env is unset_env_sentinel:
+                # In this case, `old_env` was never retrieved from the
+                # environment for whatever reason, so there's no need to
+                # reset the environment TZPATH.
+                pass
+            elif old_env is None:
                 del os.environ[path_var]
             else:
                 os.environ[path_var] = old_env  # pragma: nocover
diff --git a/Misc/NEWS.d/next/Tests/2023-03-08-13-54-20.gh-issue-102537.Vfplpb.rst b/Misc/NEWS.d/next/Tests/2023-03-08-13-54-20.gh-issue-102537.Vfplpb.rst
new file mode 100644
index 00000000000000..94d160dd4127a6
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2023-03-08-13-54-20.gh-issue-102537.Vfplpb.rst
@@ -0,0 +1,2 @@
+Adjust the error handling strategy in
+``test_zoneinfo.TzPathTest.python_tzpath_context``. Patch by Paul Ganssle.