Convert an integer to binary without using the built-in bin function

Question

This function receives as a parameter an integer and should return a list representing the same value expressed in binary as a list of bits, where the first element in the l

Answer 1

Here is the code for one that I made for college. Click Here for a youtube video of the code.! https://www.youtube.com/watch?v=SGTZzJ5H-CE

__author__ = 'Derek'
print('Int to binary')
intStr = input('Give me an int: ')
myInt = int(intStr)
binStr = ''
while myInt > 0:
    binStr = str(myInt % 2) + binStr
    myInt //= 2
print('The binary of', intStr, 'is', binStr)
print('\nBinary to int')
binStr = input('Give me a binary string: ')
temp = binStr
newInt = 0
power = 0
while len(temp) > 0:   # While the length of the array if greater than zero keep looping through
    bit = int(temp[-1])   # bit is were you temporally store the converted binary number before adding it to the total
    newInt = newInt + bit * 2 ** power  # newInt is the total,  Each time it loops it adds bit to newInt.
    temp = temp[:-1]  # this moves you to the next item in the string.
    power += 1  # adds one to the power each time.
print("The binary number " + binStr, 'as an integer is', newInt)

Answer 2

Not the pythonic way...but still works:

def get_binary_list_from_decimal(integer, bits):
    '''Return a list of 0's and 1's representing a decimal type integer.

    Keyword arguments:
    integer -- decimal type number.
    bits -- number of bits to represent the integer.

    Usage example:
    #Convert 3 to a binary list
    get_binary_list_from_decimal(3, 4)
    #Return will be [0, 0, 1, 1]
    '''
    #Validate bits parameter.
    if 2**bits <= integer:
        raise ValueError("Error: Number of bits is not sufficient to \
                          represent the integer. Increase bits parameter.")

    #Initialise binary list
    binary_list = []
    remainder = integer
    for i in range(bits-1, -1, -1):
        #If current bit value is less than or equal to the remainder of 
        #the integer then bit value is 1.
        if 2**i <= remainder:
            binary_list.append(1)
            #Subtract the current bit value from the integer.
            remainder = remainder - 2**i
        else:
            binary_list.append(0)

    return binary_list

Example of how to use it:

get_binary_list_from_decimal(1, 3)
#Return will be [0, 0, 1]

Answer 3

Just sharing a function that processes an array of ints:

def to_binary_string(x):
    length = len(bin(max(x))[2:])

    for i in x:
        b = bin(i)[2:].zfill(length)

        yield [int(n) for n in b]

Test:

x1 = to_binary_string([1, 2, 3])
x2 = to_binary_string([1, 2, 3, 4])

print(list(x1)) # [[0, 1], [1, 0], [1, 1]]
print(list(x2)) # [[0, 0, 1], [0, 1, 0], [0, 1, 1], [1, 0, 0]]

Answer 4

Just for fun - the solution as a recursive one-liner:

def tobin(x):
    return tobin(x/2) + [x%2] if x > 1 else [x]

Answer 5

You can use numpy package and get very fast solution:

python -m timeit -s "import numpy as np; x=np.array([8], dtype=np.uint8)" "np.unpackbits(x)"
1000000 loops, best of 3: 0.65 usec per loop

python -m timeit "[int(x) for x in list('{0:0b}'.format(8))]"
100000 loops, best of 3: 3.68 usec per loop

unpackbits handles inputs of uint8 type only, but you can still use np.view:

python -m timeit -s "import numpy as np; x=np.array([124567], dtype=np.uint64).view(np.uint8)" "np.unpackbits(x)"
1000000 loops, best of 3: 0.697 usec per loop

Answer 6

def nToKBit(n, K=64):
   output = [0]*K

   def loop(n, i):
       if n == 0: 
           return output
       output[-i] = n & 1
       return loop(n >> 1, i+1)

   return loop(n, 1)