python - Why my using memo didn't raise the efficiency at all? -

i doing exercise in think in python, using memo calculate fibonacci sequence far more efficiency not using one. when implemented , testing time consumed, find running time not reduced @ all. know there wrong program, please tell me went wrong. many thanks.

import time  known = {0:0,1:1} def fibonacci_memo(n):     """return nth number of fibonacci sequence     using memo raise efficiency"""     if n in known:         return known[n]      res = fibonacci(n-1) + fibonacci(n-2)     known[n] = res     return res  def fibonacci(n):     """return nth number of fibonacci sequence     without using memo"""     if n == 0:         return 0     if n == 1:         return 1     return fibonacci(n-1) + fibonacci(n-2)  if __name__ == '__main__':     start = time.clock()     print fibonacci_memo(32)     elaspsed = time.clock() - start     print 'using memo time used: ' + str(elaspsed)      start = time.clock()     print fibonacci(32)     elaspsed = time.clock() - start     print 'without using memo time used: ' + str(elaspsed) 

the output like:

2178309 using memo time used: 1.83040345779 2178309 without using memo time used: 1.792043347 

your fibonacci_memo function isn't calling recursively, it's calling original (non-memoized) fibonacci function.