Recursion in is power function in Python

Question

I'm doing my course exercise that states the following:

A number a is a power of b if:

it is divisible by b
a/b is a power of b.

Write a function called is_power that takes parameters a and b and returns True if a is a power of b.

However, I have to do it using recursion and somehow using the following function:

def is_divisible(x, y):
    if x % y == 0:
        return True
    else:
        return False

I don't know exactly where they relate to each other but yeah, that's what I'm supposed to do.

What I did so far (without using the above function) is:

def is_power(a, b):
    while a % b == 0:
        if a == b: return True
        a = a / b
    return False

print(10, 2)

Thoughts on why I have no output/how to relate the is_divisible function to is_power?

check your indentation for print and within function def is_power — chickity china chinese chicken
– chickity china chinese chicken, Commented Feb 27, 2019 at 6:56
there are comment elements if x % y == 0: and while a % b == 0: could probably replace one with the other using function call — chickity china chinese chicken
– chickity china chinese chicken, Commented Feb 27, 2019 at 7:01

Bharadwaj Swaminathan · Accepted Answer · 2019-02-27 07:06:55Z

3

If a is a power of b, then a is divisible by b. Logically the contrapositive is also true i.e. if a is not divisible by b, then a is not a power of b. This is where your is_divisible function possibly comes in - to break out of the recursion, not to propagate it.

In case is_divisible(a, b) returns True, then you go to your second condition, a/b is a power of b. Do we have a function that when given two numbers checks if one of them is a power of the other? This is the condition to propagate the recursion.

Think about what your base case will be if a does happen to be a power of b.

answered Feb 27, 2019 at 7:06

Bharadwaj Swaminathan

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