python: Convert os.open(…, O_EXCL) to open(…, "x").

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/cache.py

@@ -85,13 +85,10 @@ def get_or_create_key_prefix() -> str:
 
     filename = os.path.join(settings.DEPLOY_ROOT, "var", "remote_cache_prefix")
     try:
-        fd = os.open(filename, os.O_CREAT | os.O_EXCL | os.O_RDWR, 0o444)
-        prefix = secrets.token_hex(16) + ':'
-        # This does close the underlying file
-        with os.fdopen(fd, 'w') as f:
+        with open(filename, 'x') as f:
+            prefix = secrets.token_hex(16) + ':'
             f.write(prefix + "\n")
-    except OSError:
-        # The file already exists
+    except FileExistsError:
         tries = 1
         while tries < 10:
             with open(filename) as f:

zerver/management/commands/export.py

@@ -173,7 +173,8 @@ class Command(ZulipBaseCommand):
 
         tarball_path = output_dir.rstrip("/") + ".tar.gz"
         try:
-            os.close(os.open(tarball_path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o666))
+            with open(tarball_path, "x"):
+                pass
         except FileExistsError:
             raise CommandError(f"Refusing to overwrite existing tarball: {tarball_path}. Aborting...")