Python function to count divisible numbers in a list?

Question

I need to write a python function that takes a list as the input and calculates the number of numbers divisible by some other number, n. This is the code I have so far:

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Could someone advice me on what approach to take, please?

I tried a for loop that finds the divisible numbers and adds them to a counter, but that is not working.

Asked By: Alexandra Barraza

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Source

Answer 1

You’re returning the length of an integer, count, when you probably want to return the count itself:

def count_divisible(lst, n):
    count = 0
    for i in lst:
        if i % n == 0:
            count += 1
    return count

You can shorten your function and make it safer by checking each item is actually an int or a float:

def count_divisible_short_and_safe(lst: list, n: int) -> int:
    return len([x for x in lst if isinstance(x, (int, float)) and x % n == 0])

assert count_divisible_short_and_safe([2,3,4,5, "foo"], 2) == 2

Answered By: Danielle M.

Answer 2

The error message clearly indicated the problem. So you could fix it and make it working like this:


def count_divisible(L, n):
    count = 0
    for x in L:
        if x % n == 0:
            count += 1
    return count                  # just return the counts

# version 2 - Generator Expression 
def count_divisible2(L, n):
    return sum(1 for x in L if not x % n)

if __name__ == '__main__':
    assert count_divisible([2,3,4,5], 2) == 2

Answered By: Daniel Hao

Python function to count divisible numbers in a list?

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