Binary to decimal and vice-versa in python

Write Python code for converting a decimal number to it’s binary equivalent and vice-versa.

Example:

From decimal to binary
Input : 8
Output : 1 0 0 0

From binary to decimal
Input : 100
Output : 4

Decimal to binary

Keep calling conversion function with n/2  till n > 1,
later perform n % 1 to get MSB of converted binary number.  
Example :- 7
1). 7/2 = Quotient = 3(greater than 1), Remainder = 1.
2). 3/2 = Quotient = 1(not greater than 1), Remainder = 1.
3). 1%2 = Remainder = 1.
Therefore, answer is 111.

Python3

# Function to print binary number for the
# input decimal using recursion
def decimalToBinary(n):

    if(n > 1):
        # divide with integral result
        # (discard remainder)
        decimalToBinary(n//2)


    print(n%2, end=' ')



# Driver code
if __name__ == '__main__':
    decimalToBinary(8)
    print("\n")
    decimalToBinary(18)
    print("\n")
    decimalToBinary(7)
    print("\n")

Output: 

1 0 0 0 
1 0 0 1 0 
1 1 1 

Decimal to binary using bin():

Python3

# Function to convert Decimal number
# to Binary number

def decimalToBinary(n):
    return bin(n).replace("0b","")

# Driver code
if __name__ == '__main__':
    print(decimalToBinary(8))
    print(decimalToBinary(18))
    print(decimalToBinary(7))

Output: 

1000
10010
111

Binary to decimal

Example -: 1011
1). Take modulo of given binary number with 10. 
    (1011 % 10 = 1)
2). Multiply rem with 2 raised to the power
    it's position from right end. 
    (1 * 2^0)
    Note that we start counting position with 0. 
3). Add result with previously generated result.
    decimal = decimal + (1 * 2^0)
4). Update binary number by dividing it by 10.
    (1011 / 10 = 101)
5). Keep repeating upper steps till binary > 0.

Final Conversion -: (1 * 2^3) + (0 * 2^2) +
                 (1 * 2^1) + (1 * 2^0) = 11

Python3

# Function calculates the decimal equivalent
# to given binary number

def binaryToDecimal(binary):

    binary1 = binary
    decimal, i, n = 0, 0, 0
    while(binary != 0):
        dec = binary % 10
        decimal = decimal + dec * pow(2, i)
        binary = binary//10
        i += 1
    print(decimal)


# Driver code
if __name__ == '__main__':
    binaryToDecimal(100)
    binaryToDecimal(101)
    binaryToDecimal(1001)

Output: 

4
5
9

Binary to decimal using int():

Python3

# Function to convert Binary number
# to Decimal number

def binaryToDecimal(n):
    return int(n,2)


# Driver code
if __name__ == '__main__':
    print(binaryToDecimal('100'))
    print(binaryToDecimal('101'))
    print(binaryToDecimal('1001'))

Output: 

4
5
9

Method: Using format specifier

Python3

n =4
print('{0:b}'.format(n))

Output

100

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