''' decorator_Memoize1.py
applying a memoize decorator to a recursive function
and timing to show the improvement in speed
No keyword args allowed in the decorated function!
works with Python27 and Python33
'''

import timeit

class Memoize(object):
    """
    use as a decorator to avoid repeating calculations
    previously done by the decorated function
    (do not use for functions with keyword arguments)
    """
    def __init__(self,f):
        self.f = f
        self.memo = {}
    def __call__(self,*args):
        if args in self.memo:
            return self.memo[args]
        result = self.f(*args)
        self.memo[args] = result
        return result

def use_timeit(stmt, setup, passes=1000000):
    """
    use module timeit to time a statement stmt
    (this can be a function call or a code segment)
    for time consuming functions use fewer passes to save time
    setup gives information where too find variables/functions
    for instance -->
    stmt = 'myfunction(x)'
    setup = 'from __main__ import myfunction, x'
    """
    t = timeit.Timer(stmt=stmt, setup=setup)
    # 1000000 passes is default
    # elapsed is the time in microseconds/pass
    elapsed = (1000000//passes * t.timeit(number=passes))
    print( "%s takes %0.3f micro-seconds/pass" % (stmt, elapsed) )

@Memoize
def fibo1(n):
    """
    use recursion to get Fibonacci number for n
    not very efficient because of the many function calls
    """
    if n < 2:
        return n
    else:
        return fibo1(n - 1) + fibo1(n - 2)

# timing ...
print("first pass:")
stmt = 'fibo1(30)'
setup = 'from __main__ import fibo1'
passes = 1
use_timeit(stmt, setup, passes)

print("second pass:")
stmt = 'fibo1(30)'
setup = 'from __main__ import fibo1'
passes = 1
use_timeit(stmt, setup, passes)

# testing ...
print(fibo1(30))  # 832040

""" result ...
with the @Memoize decorator ...
first pass:
fibo1(30) takes 106.077 micro-seconds/pass
second pass:
fibo1(30) takes 2.281 micro-seconds/pass

without (commented out) the @Memoize decorator ...
first pass:
fibo1(30) takes 875692.257 micro-seconds/pass
second pass:
fibo1(30) takes 877517.997 micro-seconds/pass
"""

vegaseat, this must be the commented out test version
replace
#@Memoize
with
@Memoize
to get the working version

Edited 3 Years Ago by ZZucker

""" result ...
with the @Memoize decorator ...
first pass:
fibo1(30) takes 106.077 micro-seconds/pass
second pass:
fibo1(30) takes 2.281 micro-seconds/pass
without (commented out) the @Memoize decorator ...
first pass:
fibo1(30) takes 875692.257 micro-seconds/pass
second pass:
fibo1(30) takes 877517.997 micro-seconds/pass
"""

Or wasn't that clear enough?
His first test was indeed with @Memoize, 2nd was with that commented, so that the results yeld different timings.

I guess I am getting old and left the # in from the last timing test. I prefer to post a working version and corrected it, thanks.

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