CODEWITHSUNDEEP
python-3.xwhile-loop
o__b
o__b

Reputation: 21

python3 function to check if parameter is a power of 2 with a while loop and without using math function

Learning about functions in python3. A course question was to define a function using a while loop (and without using the math function) that determines if a parameter is a power of 2. If it is, return True. If it is not, return False. Here is the starting code:

def is_power_of_two(n):
  # Check if the number can be divided by two without a remainder
  while n % 2 == 0:
    n = n / 2
  # If after dividing by two the number is 1, it's a power of two
  if n == 1:
    return True
  return False
  

print(is_power_of_two(0)) # Should be False
print(is_power_of_two(1)) # Should be True
print(is_power_of_two(8)) # Should be True
print(is_power_of_two(9)) # Should be False

I can find examples with loops (other than while) and when using the math function, but am at a loss without either of those options.

Upvotes: 1

Views: 3107

Answers (3)

Julio Gtz - pezondechita
Julio Gtz - pezondechita

Reputation: 1

You can use break to exit the infinite loop:

def is_power_of_two(n):
  # Check if the number can be divided by two without a remainder
  while n % 2 == 0:
    if(n==0): 
      break
    n = n / 2
  # If after dividing by 2 the number is 1, it's a power of two
  if n == 1:
    return True
  return False

Upvotes: 0

Nikos M.
Nikos M.

Reputation: 8325

def is_power_of_two(n):
  # Check if the number can be divided by two without a remainder
  # special cases: 0, because 0 % 2 = 0
  # you can either use the n > 0 extra test below
  # if n == 0: return False # or an explicit test for zero
  while (n > 0) and (n % 2 == 0): n = n / 2
  # If after dividing by two the number is 1, it's a power of two
  return n == 1

Online example

Upvotes: 0

paime
paime

Reputation: 3542

n=0 is a special case since 0 % 0 == 0. That's why you had an infinite loop.

You can also simplify your return statement by using return n == 1

The function:

def is_power_of_two(n): 
    if n  == 0: 
        return False 

    while n % 2 == 0: 
        n = n / 2 

    return n == 1

tests:

print(is_power_of_two(0)) # Should be False 
print(is_power_of_two(1)) # Should be True 
print(is_power_of_two(8)) # Should be True 
print(is_power_of_two(9)) # Should be False                                                   
print(is_power_of_two(8.1)) # Should be False

output:

False
True
True
False
False

Upvotes: 2

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