Coderbyte Python Challenge: KaprekarsConstant

KaprekarsConstant.py

# Using the Python language, have the function KaprekarsConstant(num) take
# the num parameter being passed which will be a 4-digit number with at least
# two distinct digits.

# Your program should perform the following routine on the number:
# Arrange the digits in descending order and in ascending order
# subtract the smaller number from the bigger number. Then repeat the previous step.

# Performing this routine will always cause you to reach a fixed number: 6174.

# For example: if num is 3524 your program should return 3 because of the following steps:
# (1) 5432 - 2345 = 3087, (2) 8730 - 0378 = 8352, (3) 8532 - 2358 = 6174. 

# Assumes number with 4 digits given

def KaprekarsConstant(num): 

    # Set var iterations to return later
    iterations = 0

    # Sort the numbers (asc by default)
    sort_num = sorted(str(num))
    # Join the list into a string
    num_str = ''.join(sort_num)

    # Loop until we find 6174
    while num != 6174:
        sort_num = sorted(str(num)) # Sort numbers
        num_str = ''.join(sort_num) # Join to create a string
        num_asc = int(num_str) # Create ascending number
        num_desc = num_str[::-1] # Get descending number
        
        # Create for loop to add 0's to decending number length = 4
        for x in range(len(num_desc),4):
            num_desc = num_desc + '0'
            x += 1
        num_desc = int(num_desc)

        # Count iterations
        iterations += 1
        # Get new number
        num = num_desc - num_asc

    return iterations
      
print(KaprekarsConstant(input()))