# HW 02

# Q1: Product

def product(n, f):
    sum = 1
    while n:
        sum *= f(n)
        n -= 1
    return sum

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注意运算次序，题目很简单！

    while n > 0:
        base = combiner(base, f(n))
        n -= 1
    return base

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结果：

>>> accumulate(lambda x, y: 2 * (x + y), 2, 3, square)
106

# Error: expected
#     58
# but got
#     106

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def summation_using_accumulate(n, f):
    return accumulate(add,0,n,f)

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def product_using_accumulate(n, f):
    return accumulate(mul,1,n,f)

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def make_repeater(h, n):
    return accumulate(compose1,identity,n,lambda k:h)

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