Check Power of 2 in Python

What You’ll Learn

Powers of two are numbers like 1, 2, 4, 8, 16… — each is 2^k for some whole k >= 0. In binary they have exactly one set bit. This tutorial covers the classic n & (n - 1) trick, a divide-by-2 loop, a live checker, worked Python examples, edge cases, and complexity.

📝 Problem & Approach

Given an integer n, decide whether it is a power of two (2^k for some k >= 0).

# 16 -> 10000 binary  -> one set bit  -> yes
# 8  -> 1000           -> yes
# 6  -> 110            -> two bits    -> no
# 1  -> 1              -> 2^0         -> yes

Inputs & Outputs

Minimal workflow

function is_power_of_two_bitwise(n):
    if n <= 0:
        return false
    return (n & (n - 1)) == 0

function is_power_of_two_loop(n):
    if n <= 0:
        return false
    while n > 1 and n mod 2 == 0:
        n = n / 2
    return n == 1

Method comparison

🔮 Live Preview

Uses positive-check plus the bitwise rule, and shows binary for small n.

Press “Run check” to see verdict.

Examples Gallery

Three complete Python programs — bitwise check for 16, list powers from 1 to 20, and a divide-by-2 loop without bitwise operators. Click View Output to reveal sample console results.

def is_power_of_two(num: int) -> bool:
    return num > 0 and (num & (num - 1)) == 0


number = 16
if is_power_of_two(number):
    print(f"{number} is a power of 2.")
else:
    print(f"{number} is not a power of 2.")

16 is a power of 2.

def is_power_of_two(num: int) -> bool:
    return num > 0 and (num & (num - 1)) == 0


print("Power of 2 in the range 1 to 20:")
for i in range(1, 21):
    if is_power_of_two(i):
        print(i, end=" ")

Power of 2 in the range 1 to 20:
1 2 4 8 16 

def is_power_of_two(num: int) -> bool:
    if num <= 0:
        return False
    while num > 1 and num % 2 == 0:
        num //= 2
    return num == 1


for value in (1, 8, 6, 16, 0):
    label = "yes" if is_power_of_two(value) else "no"
    print(f"{value}: {label}")

1: yes
8: yes
6: no
16: yes
0: no

🔎 Worked Walkthrough — 8 vs 6

Compare the bitwise rule on a yes case and a no case.

One set bit clears to zero under AND; multiple set bits leave leftovers.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

Prefer the bitwise check in interviews unless asked to avoid bit operators.

💡 Best Practices