[issue13177] Avoid chained exceptions in lru_cache

[Raymond Hettinger]

Raymond Hettinger <raymond.hettinger at gmail.com> added the comment:

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

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue13177>
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