is_power_of_two.py

"""
Author  : Alexander Pantyukhin
Date    : November 1, 2022

Task:
Given a positive int number. Return True if this number is power of 2
or False otherwise.

Implementation notes: Use bit manipulation.
For example if the number is the power of two it's bits representation:
n     = 0..100..00
n - 1 = 0..011..11

n & (n - 1) - no intersections = 0

New Implementation Author: Arun
Date: 16th October, 2025

Change Notes:
- Added type checks and value checks for robustness.
- Added an alternative method using math.log2 for educational purposes.

New Implementation Details:
- The function raises a ValueError if the input number is negative.
- The function raises a TypeError if the input is not an integer.
- Uses math.log2 to get the exponent and checks if it's an integer.
- For all powers of 2, log2 will yield an integer value.
- For non-powers of 2, log2 will yield a non-integer value.
"""


def is_power_of_two(number: int) -> bool:
    """
    Return True if this number is power of 2 or False otherwise.

    >>> is_power_of_two(0)
    True
    >>> is_power_of_two(1)
    True
    >>> is_power_of_two(2)
    True
    >>> is_power_of_two(4)
    True
    >>> is_power_of_two(6)
    False
    >>> is_power_of_two(8)
    True
    >>> is_power_of_two(17)
    False
    >>> is_power_of_two(-1)
    Traceback (most recent call last):
        ...
    ValueError: number must not be negative
    >>> is_power_of_two(1.2)
    Traceback (most recent call last):
        ...
    TypeError: unsupported operand type(s) for &: 'float' and 'float'

    # Test all powers of 2 from 0 to 10,000
    >>> all(is_power_of_two(int(2 ** i)) for i in range(10000))
    True
    """
    if number < 0:
        raise ValueError("number must not be negative")
    return number & (number - 1) == 0


def is_power_of_two_math(number: int) -> bool:
    from math import log2

    """
    Alternative method using math.log2 to check if number is a power of 2.

    >>> is_power_of_two_math(0)
    True
    >>> is_power_of_two_math(1)
    True
    >>> is_power_of_two_math(2)
    True
    >>> is_power_of_two_math(6)
    False
    >>> is_power_of_two_math(16)
    True
    """
    if not isinstance(number, int):
        raise TypeError("number must be an integer")
    if number < 0:
        raise ValueError("number must not be negative")

    if number == 0:
        return True

    value = log2(number)
    return value == int(value)


if __name__ == "__main__":
    import doctest

    doctest.testmod()