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One possibility is to move the call to user_function() outside of the KeyError exception handler so that user exceptions won't be chained:
def wrapper(*args, **kwds):
 nonlocal hits, misses
 key = args
 if kwds:
 key += kwd_mark + tuple(sorted(kwds.items()))
 try:
 with lock:
 result = cache[key]
 cache_renew(key) # record recent use of this key
 hits += 1
 return result
 except KeyError:
 pass
 result = user_function(*args, **kwds)
 with lock:
 cache[key] = result # record recent use of this key
 misses += 1
 if len(cache) > maxsize:
 cache_popitem(0) # purge least recently used cache entry
 return result