Backport PR #21621: Fix GhostScript error handling types

jklymak · meeseeksmachine · commit b6970a313a60 · 2021-11-13T09:32:12.000Z
diff --git a/lib/matplotlib/testing/compare.py b/lib/matplotlib/testing/compare.py
@@ -136,9 +136,7 @@ def encode_and_escape(name):
         self._proc.stdin.flush()
         # GS> if nothing left on the stack; GS<n> if n items left on the stack.
         err = self._read_until((b"GS<", b"GS>"))
-        stack = ""
-        if err.endswith(b"GS<"):
-            stack = self._read_until(b">")
+        stack = self._read_until(b">") if err.endswith(b"GS<") else b""
         if stack or not os.path.exists(dest):
             stack_size = int(stack[:-1]) if stack else 0
             self._proc.stdin.write(b"pop\n" * stack_size)
