Allow ISO-8601 24:00 alternative to midnight on datetime.datetime.fromisoformat()

TizzySaurus · TizzySaurus · commit 0b4ac70a7f45 · 2023-06-16T12:03:24.000+01:00
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
@@ -5494,6 +5494,22 @@ datetime_fromisoformat(PyObject *cls, PyObject *dtstr)
         goto error;
     }
 
+    if (
+        (hour == 24 && minute == 0 && second == 0 && microsecond == 0) && // provided alternate to midnight of next day
+        (month <= 12 && day <= days_in_month(year, month)) // month and day component was previously valid
+    ) {
+        // Calculate midnight of the next day
+        hour = 0;
+        day += 1;
+        if (day > days_in_month(year, month)) {
+            day = 1;
+            month += 1;
+            if (month > 12) {
+                month = 1;
+                year += 1;
+            }
+        }
+    }
     PyObject *dt = new_datetime_subclass_ex(year, month, day, hour, minute,
                                             second, microsecond, tzinfo, cls);
 
