Coding question

[doeman]

Could someone help me with this. How do i make a recursive program that returns sum of 1**3 + 2**3 + ... + n**3?

[Gribouillis]

A recursive way

def sum_cubes(n):
    if n <= 0:
        if n < 0:
            raise ValueError
        else:
            return 0
    else:
        return n ** 3 + sum_cubes(n-1)

if __name__ == "__main__":
    print sum_cubes(10)

and a non recursive way

def sum_cubes2(n):
    if n < 0:
        raise ValueError
    res = 0
    while n:
        res += n ** 3
        n -= 1
    return res

[ZZucker]

Here is another way you can skin it:

def sum_cube(n, sum=0):
    if n > 0:
        x = n**3
        return sum_cube(n-1, sum+x)
    else:
        return sum

print sum_cube(5)  # 225

[doeman]

Here is another way you can skin it:

def sum_cube(n, sum=0):
    if n > 0:
        x = n**3
        return sum_cube(n-1, sum+x)
    else:
        return sum

print sum_cube(5)  # 225

This is a recursive way right?

[ZZucker]

Recursive means that the function calls itself, and it does so in line 4.
In Gribouillis's code it does so in line 8.

[BearofNH]

Here's another recursive way although it is kind of cheating:

>>> sum_cube = lambda N: eval(["0","(N*N*N) + sum_cube(N-1)"][N>0])
>>> sum_cube(10)
3025

[ZZucker]

Wow BearofNH, the Auberge Pyrenees-Cevennes of Python.