Optimization: only analyze traceback if needed

pyfakefs/fake_open.py

@@ -89,6 +89,7 @@ def fake_open(
     if is_called_from_skipped_module(
         skip_names=skip_names,
         case_sensitive=filesystem.is_case_sensitive,
+        check_open_code=sys.version_info >= (3, 12),
     ):
         return io_open(  # pytype: disable=wrong-arg-count
             file,

pyfakefs/helpers.py

@@ -478,12 +478,19 @@ def putvalue(self, value: bytes) -> None:
         self._bytestream.write(value)
 
 
-def is_called_from_skipped_module(skip_names: list, case_sensitive: bool) -> bool:
+def is_called_from_skipped_module(
+    skip_names: list, case_sensitive: bool, check_open_code: bool = False
+) -> bool:
     def starts_with(path, string):
         if case_sensitive:
             return path.startswith(string)
         return path.lower().startswith(string.lower())
 
+    # in most cases we don't have skip names and won't need the overhead
+    # of analyzing the traceback, except when checking for open_code
+    if not skip_names and not check_open_code:
+        return False
+
     stack = traceback.extract_stack()
 
     # handle the case that we try to call the original `open_code`
@@ -494,12 +501,15 @@ def starts_with(path, string):
     # -3: fake_io.open: 'return fake_open('
     # -4: fake_io.open_code : 'return self._io_module.open_code(path)'
     if (
-        sys.version_info >= (3, 12)
+        check_open_code
         and stack[-4].name == "open_code"
         and stack[-4].line == "return self._io_module.open_code(path)"
     ):
         return True
 
+    if not skip_names:
+        return False
+
     caller_filename = next(
         (
             frame.filename