abs() is a built-in function in Python programming language which gives a positive value of any number in return. It means it converts any negative number into a positive number and positive numbers remain unchanged.#Python 3 program to convert n into # negative base form # Method to convert n to base negBase def toNegativeBase(n, negBase): # If n is zero then in any base it # will be 0 only if (n == 0): return "0" converted = "01" while (n != 0): # Get remainder by negative base, # it can be negative also remainder = n % (negBase) n = int(n/negBase) # if remainder is negative, add # abs(base) to it and add 1 to n if (remainder < 0): remainder += ((-1) * negBase) n += 1 # convert remainder to string add # into the result converted = str(remainder) + converted return converted # Driver Code if __name__ == '__main__': n = 13 negBase = -2 print(toNegativeBase(n, negBase)) # This code is contributed by #SP85 (this is by me) From c++ program vice versa - python

You want to negate it only if the start is greater than the end.

if start > end:
    amount = -amount

Or you can tuck that right into the range() call:

for i in range(start, end, -amount if start > end else amount):