A couple of minor updates

restrictedpython_code_eval.py

@@ -26,10 +26,12 @@ import multiprocessing
 import os
 import platform
 import signal
+import sys
 import tempfile
 import types
 from typing import Optional, Dict, List, Any
 
+
 from collections import Counter, defaultdict
 from concurrent.futures import ThreadPoolExecutor, as_completed
 
@@ -46,7 +48,8 @@ from RestrictedPython.Guards import guarded_iter_unpack_sequence, safer_getattr,
 # patch their list implementation to allow empty lists and tuples
 def limited_list(seq=None):
     if isinstance(seq, str):
-        raise TypeError('cannot convert string to list')
+        # raise TypeError('cannot convert string to list')
+        return [c for c in seq]
     return list(seq) if seq is not None else list()
 
 
@@ -55,7 +58,8 @@ limited_builtins['list'] = limited_list
 
 def limited_tuple(seq=None):
     if isinstance(seq, str):
-        raise TypeError('cannot convert string to tuple')
+        # raise TypeError('cannot convert string to tuple')
+        return tuple([c for c in seq])
     return tuple(seq) if seq is not None else tuple()
 
 
@@ -90,6 +94,9 @@ def limited_range(iFirst, *args):
 limited_builtins['range'] = limited_range
 
 
+ALLOWED_UNDERSCORE_NAMES = ['__add__']
+
+
 def safer_getattr_allowing_string_format(object, name, default=None, getattr=getattr):
     """Getattr implementation allowing str.format(), but preventing access to
     private attributes.
@@ -98,7 +105,7 @@ def safer_getattr_allowing_string_format(object, name, default=None, getattr=get
     http://lucumr.pocoo.org/2016/12/29/careful-with-str-format/
 
     """
-    if name.startswith('_'):
+    if name.startswith('_') and name not in ALLOWED_UNDERSCORE_NAMES:
         raise AttributeError(
             '"{name}" is an invalid attribute name because it '
             'starts with "_"'.format(name=name)
@@ -394,6 +401,11 @@ def _check_correctness(check_program, timeout, task_id, completion_id,
     return out_dict
 
 
+class LimitedSysModule:
+    def __init__(self):
+        self.maxsize = sys.maxsize
+
+
 class AllowListImporter:
     def __init__(self, allowed_imports: List[str]):
         self.allowed_imports = allowed_imports
@@ -408,6 +420,16 @@ class AllowListImporter:
         else:
             package_name = name
 
+        if package_name == 'sys':
+            limited_sys = LimitedSysModule()
+            if name is None:
+                return limited_sys
+            
+            if hasattr(limited_sys, name):
+                return getattr(limited_sys, name)
+
+            raise ImportError(f"Cannot import {name} from limited sys implementation.")
+
         if package_name in self.allowed_imports:
             return importlib.__import__(name, globals, locals, fromlist, level)