Today I challenged myself to compute a way to find if a number is happy or not.

So what is a happy number?

To quote the wikipedia page:

A happy number is defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits in base-ten, and repeat the process until the number either equals 1 (where it will stay), or it loops endlessly in a cycle that does not include 1. Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers (or sad numbers).

Now that we know what a happy number is let's code !

Let's get a positive number from the user

For this part I will use:

  • input() to get the input from the user.
  • int() to convert the output of input() to integer.
  • abs() to return the absolute value of the given number.
def given_number():
    This function ask the user for a number and return it so it
    can be usable by other functions.

    Returns: int
        The given number.

    # We use while because I want to infinite ask for a number
    # if the user do not give us a number.
    while True:
        # because the use can input anything, I choosed to
        # handle  the exception if the user do not give us a
        # number.
        # This way we keep asking untill the user give us a
        # number.
            initial_number = abs(int(input("Give us a number ")))
        except ValueError:

    return initial_number

Spliting digits

Because to compute the happy numbers checking we have to calculate the sum of the square of its digits in base-ten. So, I choosed to directly split each digit of the sequence before doing the calculations.

For this part I will use:

  • int() to convert each digits to integer.
  • str() to convert the given number to string.
  • map() to iterate through the converted string.
def split_digits(digits):
    This function split each digits of a given number.

        - digits: int
            The number to split.

    Returns: list
        A list with each digit.

    # We convert the given number to string first.
    # Then we the iterate over each characters which are
    # converted as integer.
    # As map return a list, and int replace the current
    # iteration to integer, we get the list of each digits
    # of the number.
    return map(int, str(digits))

Calculation of the sum of the square of each digits

For this part I will use:

  • pow() to calculate the square of each digits.
def calculation(digits):
    This function return the calculation of the sum of the square
    of each digits.

    Returns: int
        The result of the recursively sum of squares of each

    # This variable is used to store the calculation results.
    result = 0

    # We use for to iterate through the list of digits given by
    # split_digits().
    for digit in digits:

        # We append the square of the current digits to result
        # this way we can return the results once we finished
        # to iterate through the list of  digits.
        result += pow(digit, 2)

    return result

Is a number happy ?

Because I wanted to be eable to check if a number is happy from another script, I choosed to write a function which will tell us if a number is happy (True) or unhappy (False).

As I also want to see the sequence of the results of calculation() when I will work with this function, I introduced between everything a switch which if True will give us a tuple of (True, [results of calculation()]) if the number is happy and (False, [results of calculation()]) if the number is unhappy.

Finally please note that as I did not want to wait for an endless loop, I choosed to check if the result of calculation() was already in our list of results. If it is the case then we have an unhappy number.

For this part I will use:

def is_happy(number, return_sequence=False):
    This function check if a number is happy or not.

        - number: int
            The number to check.
        - return_sequence: bool
            If True we return the sequence of results.

    Returns: bool or tuple
        - True: number is happy.
        - False: number is unhappy.
        - tuple: if return_sequence == True
            - We return (True|False, past_results)

    # This will save the list of previous or past results.
    past_results = []

    list_of_digits = split_digits(number)

    # I choosed to to an endless loop because we do not know
    # where we are going and which path to choose.
    while True:
        current_result = calculation(list_of_digits)

        if current_result not in past_results:
            if current_result != 1:
                list_of_digits = split_digits(current_result)
            elif return_sequence:
                return (True, past_results)
            return True
        elif return_sequence:
            return (False, past_results)
        return False

What if we want to run the scripts ?

Well, to run it as a script with for example python I added the following to the script.

Please note the usage of if __name__ == '__main__': which avoid the script running when we are exporting for example is_happy() for another script or module.

Is this part I will use:

if __name__ == '__main__':
    NUMBER = given_number()

    if is_happy(NUMBER):
        print('%d is a happy number' % NUMBER)
        print('%d is an unhappy number' % NUMBER)

Final script