[live] Restore sys.stderr when an exception happens during a refresh

Without this the user sees no error displayed in their terminal - and even capturing the exception and displayed their own error reporting is ineffective.

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Allow exceptions that are raised while a Live is rendered to be displayed and/or processed https://github.com/Textualize/rich/pull/2305
+
 ## [12.4.4] - 2022-05-24
 
 ### Changed

rich/live.py

@@ -118,7 +118,15 @@ def start(self, refresh: bool = False) -> None:
             self._enable_redirect_io()
             self.console.push_render_hook(self)
             if refresh:
-                self.refresh()
+                try:
+                    self.refresh()
+                except Exception:
+                    # If refresh fails, we want to stop the redirection of sys.stderr,
+                    # so the error stacktrace is properly displayed in the terminal.
+                    # (or, if the code that calls Rich captures the exception and wants to display something,
+                    # let this be displayed in the terminal).
+                    self.stop()
+                    raise
             if self.auto_refresh:
                 self._refresh_thread = _RefreshThread(self, self.refresh_per_second)
                 self._refresh_thread.start()