[3.13] gh-156067: Fix two error handling issues in `_zoneinfo.load_data()` (GH-156068) (#156090)

https://github.com/python/cpython/commit/200b98b9fb301dd4ccf93db0516d6f08f661feed
commit: 200b98b9fb301dd4ccf93db0516d6f08f661feed
branch: 3.13
author: Miss Islington (bot) <[email protected]>
committer: StanFromIreland <[email protected]>
date: 2026-08-20T09:37:56Z
summary:

[3.13] gh-156067: Fix two error handling issues in `_zoneinfo.load_data()` (GH-156068) (#156090)

(cherry picked from commit 21a6a8a89246cb3c78d1e517084caf2d47c822f7)

Co-authored-by: Stan Ulbrych <[email protected]>

files:
A Misc/NEWS.d/next/Library/2026-08-19-21-01-19.gh-issue-156067.1CXkqc.rst
M Modules/_zoneinfo.c

diff --git a/Misc/NEWS.d/next/Library/2026-08-19-21-01-19.gh-issue-156067.1CXkqc.rst b/Misc/NEWS.d/next/Library/2026-08-19-21-01-19.gh-issue-156067.1CXkqc.rst
new file mode 100644
index 00000000000000..af4c778ece5d70
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-19-21-01-19.gh-issue-156067.1CXkqc.rst
@@ -0,0 +1,2 @@
+Fix error handling in the :mod:`zoneinfo` accelerator module when a
+transition index is ``-1`` or a TZ string's ``__bool__`` raises.
diff --git a/Modules/_zoneinfo.c b/Modules/_zoneinfo.c
index be24b4ceaacf37..54dab325704813 100644
--- a/Modules/_zoneinfo.c
+++ b/Modules/_zoneinfo.c
@@ -1068,7 +1068,7 @@ load_data(zoneinfo_state *state, PyZoneInfo_ZoneInfo *self, PyObject *file_obj)
         }
 
         Py_ssize_t cur_trans_idx = PyLong_AsSsize_t(num);
-        if (cur_trans_idx == -1) {
+        if (cur_trans_idx == -1 && PyErr_Occurred()) {
             goto error;
         }
 
@@ -1179,7 +1179,12 @@ load_data(zoneinfo_state *state, PyZoneInfo_ZoneInfo *self, PyObject *file_obj)
         self->ttinfo_before = &(self->_ttinfos[0]);
     }
 
-    if (tz_str != Py_None && PyObject_IsTrue(tz_str)) {
+    int has_tz_str = PyObject_IsTrue(tz_str);
+    if (has_tz_str < 0) {
+        goto error;
+    }
+
+    if (has_tz_str) {
         if (parse_tz_str(state, tz_str, &(self->tzrule_after))) {
             goto error;
         }

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