How to Check Divisibility in Python Without the Division Pitfalls?

Checking Divisibility in Python: A Different Perspective

When faced with the task of determining whether a number is divisible by another, many developers instinctively resort to division and checking the remainder. However, this approach can lead to pitfalls, especially in the context of Python's varied interpretation of division.

In Python 2.x, the default behavior is integer division, which discards the remainder. This means that division operators will always yield an integer, regardless of the presence of a non-zero remainder. As a result, using isinstance to test for an integer doesn't provide meaningful discrimination.

In Python 3.x, on the other hand, division defaults to floating-point operations, producing floating-point values even for whole numbers. Consequently, the isinstance check will fail even when the number is divisible in the mathematical sense.

A Better Path: Modulus Operator to the Rescue

A more effective approach is to utilize the modulus operator, %. The expression n % k == 0 returns True if and only if n is evenly divisible by k. This method directly addresses the divisibility criterion without the ambiguities associated with division.

Example Solution

Armed with this knowledge, let's modify your code to correctly test for divisibility:

<code class="python">n = 0
s = 0

while n < 1001:
    if (n % 3 == 0) or (n % 5 == 0):
        s += n

    n += 1</code>

This solution uses the modulus operator to check divisibility by both 3 and 5, effectively filtering out numbers that meet either condition. The result is a more precise and robust solution for your original problem.

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