How to convert decimal to binary using algorithms in python

Question

please what is wrong with this code

def binary_converter(n):
    n = int(n)

    if n == 0:
        return '0'

    elif n not in (0,255):
        return 'Invalid input'


    elif n in range (0,255):
        return binary_converter(n//2) + str(n%2)


    else:
        return 'Invalid conversion'## Heading ##

here is the test
import unittest

class BinaryConverterTestCases(unittest.TestCase):
  def test_conversion_one(self):
    result = binary_converter(0)
    self.assertEqual(result, '0', msg='Invalid conversion')

  def test_conversion_two(self):
    result = binary_converter(62)
    self.assertEqual(result, '111110', msg='Invalid conversion')

  def test_no_negative_numbers(self):
    result = binary_converter(-1)
    self.assertEqual(result, 'Invalid input', msg='Input below 0 not allowed')

  def test_no_numbers_above_255(self):
    result = binary_converter(300)
    self.assertEqual(result, 'Invalid input', msg='Input above 255 not allowed')

@DarthKotik in the test it is supposed to return an invalid input aswell. — Darkcodr
– Darkcodr, Commented Sep 16, 2016 at 19:57
@PadraicCunningham your correct but i still get an error when submitting it.. P/S it is an assignement for andela home study.. i just need advices not the full code as i really want to learn this properly. thanks all — Darkcodr
– Darkcodr, Commented Sep 16, 2016 at 19:58

Padraic Cunningham · Accepted Answer · 2016-09-16 20:38:39Z

1

First, (0, 255) is a tuple not a range of numbers so 2 in (0, 255) etc.. is going to fail, ranges are half-open so range(0,255) goes from 0...254, again 255 in range (0,255) -> False. Your third test self.assertEqual(result, '111110', msg='Invalid conversion') fails as you always add a leading "0" in your base case so you get '0111110' not '111110':

def binary_converter(n):
    n = int(n)
    if n == 0:
        return '0'
    # same as checking "if n in xrange(256)"
    if 0 <= n <= 255:
        return (binary_converter(n // 2) + str(n % 2)).lstrip("0")
    elif 0 > n or n > 255:
        return 'Invalid input'  ## Heading ##
    return 'Invalid conversion'  ## Heading ##

Once you make the changes all the tests should pass.

You could also do it iteratively:

def binary_converter(n):
    if n < 0 or n > 255:
        return "Invalid input"
    tmp = []
    while n:
        n, i = divmod(n, 2)
        tmp.append(str(i))
    return "".join(tmp[::-1] or "0")

edited Sep 16, 2016 at 20:38

answered Sep 16, 2016 at 20:23

Padraic Cunningham

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1 Comment

Darkcodr Over a year ago

you have done me a huge favour.. i failed to notice it was missing just a few bugs.. i really appreciate this, thank you very much.

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