def fib(n):
    
    if n <= 2: return n
    if n in _fib_cache: return _fib_cache[n]
    result = fib(n - 1) + fib(n - 2)
    _fib_cache[n] = result
    return result
Returns the nth value in the Fibonacci sequence.
dataset/ETHPy150Open tallstreet/Whoosh-AppEngine/src/whoosh/util.py/fib