gh-128636: Fix crash in PyREPL when os.environ is overwritten with an invalid value for mac

Lib/_pyrepl/reader.py

@@ -491,7 +491,7 @@ def get_prompt(self, lineno: int, cursor_on_line: bool) -> str:
             prompt = self.ps1
 
         if self.can_colorize:
-            t = THEME()
+            t = THEME(force_color=self.can_colorize)
             prompt = f"{t.prompt}{prompt}{t.reset}"
         return prompt
 

Lib/_pyrepl/unix_console.py

@@ -159,6 +159,7 @@ def __init__(
         self.pollob.register(self.input_fd, select.POLLIN)
         self.terminfo = terminfo.TermInfo(term or None)
         self.term = term
+        self.is_mac = platform.system() == "Darwin" and os.getenv("TERM_PROGRAM") == "Apple_Terminal"
 
         @overload
         def _my_getstr(cap: str, optional: Literal[False] = False) -> bytes: ...
@@ -339,7 +340,7 @@ def prepare(self):
         tcsetattr(self.input_fd, termios.TCSADRAIN, raw)
 
         # In macOS terminal we need to deactivate line wrap via ANSI escape code
-        if platform.system() == "Darwin" and os.getenv("TERM_PROGRAM") == "Apple_Terminal":
+        if self.is_mac:
             os.write(self.output_fd, b"\033[?7l")
 
         self.screen = []
@@ -370,7 +371,7 @@ def restore(self):
         self.flushoutput()
         tcsetattr(self.input_fd, termios.TCSADRAIN, self.__svtermstate)
 
-        if platform.system() == "Darwin" and os.getenv("TERM_PROGRAM") == "Apple_Terminal":
+        if self.is_mac:
             os.write(self.output_fd, b"\033[?7h")
 
         if hasattr(self, "old_sigwinch"):

Lib/test/test_pyrepl/test_unix_console.py

@@ -303,3 +303,19 @@ def test_getheightwidth_with_invalid_environ(self, _os_write):
             self.assertIsInstance(console.getheightwidth(), tuple)
             os.environ = []
             self.assertIsInstance(console.getheightwidth(), tuple)
+
+    @unittest.skipUnless(sys.platform == "darwin", "requires OS X")
+    def test_is_mac_with_invalid_environ(self, _os_write):
+        # gh-128636 for macOS
+        console = UnixConsole(term="xterm")
+        with os_helper.EnvironmentVarGuard() as env:
+            is_mac = os.getenv("TERM_PROGRAM") == "Apple_Terminal"
+            self.assertEqual(console.is_mac, is_mac)
+            os.environ = []
+            console.prepare()  # Need to prepare before restore
+            try:
+                console.restore()  # This should not crash
+            except (KeyError, AttributeError, TypeError) as e:
+                self.fail(f"restore() failed with invalid environ: {e}")
+
+            self.assertEqual(console.is_mac, is_mac)