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

Lib/_pyrepl/reader.py

@@ -23,6 +23,7 @@
 
 import sys
 import _colorize
+from _colorize import Syntax
 
 from contextlib import contextmanager
 from dataclasses import dataclass, field, fields
@@ -213,6 +214,7 @@ class Reader:
     lxy: tuple[int, int] = field(init=False)
     scheduled_commands: list[str] = field(default_factory=list)
     can_colorize: bool = False
+    theme: Syntax | None = None
     threading_hook: Callback | None = None
 
     ## cached metadata to speed up screen refreshes
@@ -274,6 +276,8 @@ def __post_init__(self) -> None:
         self.cxy = self.pos2xy()
         self.lxy = (self.pos, 0)
         self.can_colorize = _colorize.can_colorize()
+        if self.can_colorize:
+            self.theme = THEME()
 
         self.last_refresh_cache.screeninfo = self.screeninfo
         self.last_refresh_cache.pos = self.pos
@@ -491,7 +495,8 @@ def get_prompt(self, lineno: int, cursor_on_line: bool) -> str:
             prompt = self.ps1
 
         if self.can_colorize:
-            t = THEME()
+            t = self.theme
+            assert t is not None  # theme is set when can_colorize is True
             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"):