Merge pull request #1718 from anatoly-scherbakov/issue-1717-defined-namespace-meta-getitem-is-slow

`DefinedNamespaceMeta.__getitem__` is slow

Author: white-gecko

rdflib/namespace/__init__.py

@@ -1,5 +1,6 @@
 import logging
 import warnings
+from functools import lru_cache
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union, Iterable
 from unicodedata import category
 
@@ -184,17 +185,15 @@ def __repr__(self) -> str:
 
 
 class DefinedNamespaceMeta(type):
-    """
-    Utility metaclass for generating URIRefs with a common prefix
-
-    """
+    """Utility metaclass for generating URIRefs with a common prefix."""
 
     _NS: Namespace
     _warn: bool = True
     _fail: bool = False  # True means mimic ClosedNamespace
     _extras: List[str] = []  # List of non-pythonesque items
     _underscore_num: bool = False  # True means pass "_n" constructs
 
+    @lru_cache(maxsize=None)
     def __getitem__(cls, name: str, default=None) -> URIRef:
         name = str(name)
         if str(name).startswith("__"):