Python Program to Find Whether a Number is a Power of Two

In this tutorial, the power of 2 or not for python programming can be checked. The user gives a positive integer N and we have to check if it is equivalent to 2^x or not, where x can be zero or a number positive.

Examples:

Example1:

Input:

given number =2048

Output:

The given numb 2048 is power of 2

Example2:

Input:

given number =256

Output:

The given numb 256 is power of 2

Example3:

Input:

given number =678

Output:

The given numb 678 is not power of 2

Program to Find Whether a Number is a Power of Two in Python

There are several ways to check whether the given number is a power of 2 or not some of them are:

Using log function
Using while loop
Using Bitwise Operators
By Calculating total number of set bits

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Method #1:Using log function

This answer is just a mathematical one.
If the log2(n) of the given number n is integer than it is power of 2
Else it is not power of 2.

Below is the implementation:

# importing log from math
from math import log
# given number
numb = 2048
# given base (here it is 2 as we have to check whether it is power of 2 or not)
bas = 2
# calculating log2 of the  given numb using log function
logvalue = log(numb, bas)
# if the value is integer then it is power of 2
if (int(logvalue) == logvalue):
    print("The given numb", numb, "is power of 2")
# else it is not power of 2
else:
    print("The given numb", numb, "is not power of 2")

Output:

The given numb 2048 is power of 2

Method #2:Using while loop

Continue dividing the number into two, i.e. do n = n/2 as long as n is 1 If n percent 2 is non-zero and n is not 1 in all iteration, then n is not 2. It is a power of 2, if n becomes 1.

Below is the implementation:

# function which returns true if the given number is power of 2 else it reeturns false


def checktwoPower(numb):
    # checking if the number is 0
    if (numb == 0):
      # if the number is 0 then it is not power of 2 hence return false
        return False
    # using while loop to iterate till the number not equal to 1
    while (numb != 1):
        # if the bit is set bit then it is not power of 2 so return False
        if (numb % 2 != 0):
            return False
            # dividing n
        numb = numb // 2
    return True


# given number
numb = 2048
# passing the given number to checktwoPower function
# if the value is integer then it is power of 2
if (checktwoPower(numb)):
    print("The given numb", numb, "is power of 2")
# else it is not power of 2
else:
    print("The given numb", numb, "is not power of 2")

Output:

The given numb 2048 is power of 2

Method #3:Using Bitwise Operators

If the number is 2 power, the binary representation of only 1 bit is set.
If we remove 1 from a power number 2, then all the bits are set and the set bit is unset after the set bits (just one bits are set according to point-1)

Therefore, if a number is 2, then

numb&(numb-1) == 0

Only if N is zero is the exception to the foregoing rule. As a power of two, it will give zero which in fact is not. Therefore, we can explicitly see this in the check.

Below is the implementation:

# function which returns true if the given number is power of 2 else it reeturns false


def checktwoPower(numb):
    return numb and (not(numb & (numb-1)))


# given number
numb = 2048
# passing the given number to checktwoPower function
# if the value is integer then it is power of 2
if (checktwoPower(numb)):
    print("The given numb", numb, "is power of 2")
# else it is not power of 2
else:
    print("The given numb", numb, "is not power of 2")

Output:

The given numb 2048 is power of 2

Method #4:By Calculating total number of set bits

A simple method is to take each bit into consideration in a number (set or unset) and hold a counter to track the set bits if the total number of set bits is 1 then the number is power of 2 else it is not the power of 2

Approach:

Set the variable to say count to 0 to count the total number of set bits.
We utilize the while loop.
We’ll keep going till the number is bigger than zero (Condition of while statement)
Using the & operator, we will determine whether the last check bit is set or not.
If the check bit is 1, it indicates that the bit is set, and we increment the count.
Divide the given number by 2.
If the count is 1 then it is the power of 2 hence return true
Else return false

We use n&1 to check whether it is set bit or not.

Below is the implementation:

# function which returns true if the given number is power of 2 else it reeturns false


def checktwoPower(numb):
    # checking if the given number is greater than 1
    if numb > 1:
      # Set the variable say setbitcount to 0 to count the total number of set bits.
        setbitcount = 0
        # looping till number greater than 0 using while loop
        while(numb > 0):
            # We will get the last check bit whether it is set bit or not using & operator
            # checking if the check bit is 1 or not
            # if the check bit is 1 then increment the setbitcount
            if(numb & 1):
                setbitcount = setbitcount+1
            # divide the number by 2
            numb = numb//2
    # checking if the total number of setbits are 1 or not
    return (setbitcount == 1)


# given number
numb = 2048
# passing the given number to checktwoPower function
# if the value is integer then it is power of 2
if (checktwoPower(numb)):
    print("The given numb", numb, "is power of 2")
# else it is not power of 2
else:
    print("The given numb", numb, "is not power of 2")

Output:

The given numb 2048 is power of 2

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