How do I break an infinite Python loop?

Question

I'm looking to fix the following code, so that it can finish successfully for all numbers listed. How can I break the infinite loop that's present? Furthermore, how can I return print(is_power_of_two(8)) as True?

  # 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

the `break` is in a spot where it doesn't make any sense. Move it into the loop. — Z4-tier, Mar 29 '20 at 21:15
@Z4-tier code has been set to its default value. Where is break placed? — , Mar 29 '20 at 21:17
For which number(s) do you get an infinite loop? What is your best explanation of why? — Karl Knechtel, Mar 29 '20 at 21:17
Well, what happens if you try testing them one at a time, instead of all at once? — Karl Knechtel, Mar 29 '20 at 21:27
I get true or false. They're all rendering correctly except for 8. — , Mar 29 '20 at 21:49

lamourette jean-baptiste · Accepted Answer · 2020-03-29T22:04:38.593

2

your while condition should be :

# Check if the number can be divided by two without a remainder
  while n % 2 == 0 and n >1:
    n = n / 2

cause for the moment your code infinitely loops when n=1 cause 1%2 = 1

edited Mar 29 '20 at 22:04

answered Mar 29 '20 at 21:17

lamourette jean-baptiste

133
8

Loop is not needed there at all. – Olvin Roght Mar 29 '20 at 21:18
for sure, it was to fit his example, i'm not aware either at all with his calc method – lamourette jean-baptiste Mar 29 '20 at 21:20
this stops the loop, but I still need to check if a number is a power of 2 within this function. – Mar 29 '20 at 21:20
This works @lamourettejean-baptiste, except it still returns (is_power_of_two(8)) as False. – Mar 29 '20 at 21:26
1

yeah, that's because that's not the correct method to check if number is a power of two. I just acted to break your infinite loop. You juste got to return what @ThomasDenisReyes answers instead of making a while loop – lamourette jean-baptiste Mar 29 '20 at 21:33
@Sean, you're trying to reinvent [logarithm](https://en.wikipedia.org/wiki/Logarithm). – Olvin Roght Mar 29 '20 at 21:42
Trying, and failing! – Mar 29 '20 at 21:48
"Not quite. Remember that the goal of the function is to check if a number is a power of 2. You need to fix the infinite loop and still return the correct result." – Mar 29 '20 at 21:56
Error on line 3: while n % 2 == 0 && n > 1: ^ SyntaxError: invalid syntax – Mar 29 '20 at 21:58
replace it with while n % 2 == 0 and n > 1: – lamourette jean-baptiste Mar 29 '20 at 22:01
Just figured that out too! It works. Thanks @lamourettejean-baptiste. – Mar 29 '20 at 22:03

score 1 · Answer 2 · answered Mar 29 '20 at 21:17

1

Add and n != 0 to the while condition, so the loop will halt when n is zero.

answered Mar 29 '20 at 21:17

zmbq

38,013
14
101
171

I think, he doesn't need loop at all. – Olvin Roght Mar 29 '20 at 21:18
where does that go? – Mar 29 '20 at 21:23

Prajapati Rahul · Answer 3 · 2020-10-05T06:00:24.750

1

def is_power_of_two(n):
  # Check if the number can be divided by two without a remainder
  while n!=0 and (n % 2 == 0 or 2%n==0):
    n = n / 2
    return True
  return False

edited Oct 05 '20 at 06:00

answered Oct 05 '20 at 05:10

Prajapati Rahul

11
2

score 0 · Answer 4 · answered Mar 29 '20 at 21:16

0

import math    
math.log2(number).is_integer()

Use this. From Check if a given number is power of two in Python

answered Mar 29 '20 at 21:16

Tomás Denis Reyes Sánchez

692
6
17

score 0 · Answer 5 · answered Oct 18 '20 at 21:47

def is_power_of_two(n):

 #Check Number for Zero
  if n==0:
    return False
  else:
    # 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

score 0 · Answer 6 · answered Oct 31 '20 at 04:45

def is_power_of_two(n):
  # Check if the number can be divided by two without a remainder
  while n % 2 == 0 and n!=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

How do I break an infinite Python loop?

6 Answers6