Python Decimal to Binary converter (without using bin() or output formatting)

Question

There is no input validation for this, but that aside, I would appreciate it if anyone could help me improve the logic of this script.

import math
#Input
num = input("Enter a whole number: ")

#Floors input in case of a non whole number
decimal = math.floor(float(num))

#Variables
exp = 0
divTwo = 1
zeros = 0
total = ""
if decimal < 0:
    total += str('-')
    decimal = -decimal
if decimal == 0:
    total = str('0')
else:
    #Loops while remainder is > 0.
    while int(decimal) > 0:

        #Increases exponent by one if 2^exp is less than or equal to the remainder.
        if 2 ** exp <= int(decimal):
                exp += 1

        else: #Multiplies 2 by the exponent and places zeros in between 1s. Also subtracts from the exponent.
                exp -= 1

                #Determines whether or not to subtract from the remainder and add a '1' to the binary translation or just add a '0' to the binary translation.
                if 2 ** exp <= int(decimal):

                        #Counts how many zeros need to be added to the end of the binary translation.
                        if 2 ** exp == int(decimal):
                                divTwo = int(decimal)

                                #Loops until all remaining zeros have been accounted for.
                                while divTwo > 1:
                                        divTwo = divTwo / 2
                                        zeros += 1

                        decimal = int(decimal)
                        decimal -= 2 ** exp
                        total += str('1')

                else:
                        total += str('0')

#Places remaining zeros.
while zeros > 0:
        total += str('0')
        zeros -= 1


#Displays answer.
print ('Binary: ' + total)
input()

#
#
#Or 'bin(decimal)' works too, but this was for fun
#
#

Here is a working version of the script.

Answer 1

• You can remove half of you code.
  You need the variables exp, total and decimal. The rest are just noise.

• You should remove all the int(decimal)s, decimal is only ever subtracted from, and so it's not going to become a float. And so these are not needed.

1. You can remove all the code in if 2 ** exp == int(decimal):, instead just use exp as you do zeros.

2. You should split your while loop so that it only does one thing at a time. You want an int log and then a while loop that converts the input to binary.

3. You can replace while zeros > 0: with Pythons way to duplicate strings. 0 * zeros.

4. You should make this a function.

This leads to code like:

def binary(number): # 4
    output = ''
    if number < 0:
        output = '-'
        number = -number

    exp = 1
    while 2 ** exp <= number: # 2
        exp += 1

    while number > 0:
        exp -= 1
        if 2 ** exp <= number:
            number -= 2 ** exp
            output += '1'
        else:
            output += '0'

    return output + '0' * exp # 1, 3


number = int(input("Enter a whole number: "))
print('Binary: ' + binary(number))