Decimal to Binary

def decToBin(dec):
    binary = "";
    while(dec != 0):
        binary = str(dec%2) + binary;
        dec = int(dec/2);
    return binary;

print(decToBin(int(input("ENTER DECIMAL"))));

Binary to Decimal

def binToDec(bin):
    dec = 0;
    bin = str(bin);
    for i in range(len(bin)):
        dec += int(bin[i])*(2**(len(bin)-1-i));
    return dec;

print(binToDec(1111));

Decimal to Hexadecimal

def decToHex(dec):
    hexadecimal = "";
    while(dec != 0):
        if(dec%16 <= 10):
            hexadecimal= str(dec%16) + hexadecimal;
        elif (dec%16 == 10):
            hexadecimal= "A" + hexadecimal;
        elif (dec%16 == 11):
            hexadecimal= "B" + hexadecimal;
        elif (dec%16 == 12):
            hexadecimal= "C" + hexadecimal;
        elif (dec%16 == 13):
            hexadecimal= "D" + hexadecimal;
        elif (dec%16 == 14):
            hexadecimal= "E" + hexadecimal;
        elif (dec%16 == 15):
            hexadecimal= "F" + hexadecimal;
        dec = int(dec/16);
    return hexadecimal;

print(decToHex(1000));

3E8

Hexadecimal to Decimal

def decToHex(decimal_number):
    hexadecimal_number = ""

    while decimal_number > 0:
        remainder = decimal_number % 16

        if remainder == 0:
            hexadecimal_number = "0" + hexadecimal_number
        elif remainder == 1:
            hexadecimal_number = "1" + hexadecimal_number
        elif remainder == 2:
            hexadecimal_number = "2" + hexadecimal_number
        elif remainder == 3:
            hexadecimal_number = "3" + hexadecimal_number
        elif remainder == 4:
            hexadecimal_number = "4" + hexadecimal_number
        elif remainder == 5:
            hexadecimal_number = "5" + hexadecimal_number
        elif remainder == 6:
            hexadecimal_number = "6" + hexadecimal_number
        elif remainder == 7:
            hexadecimal_number = "7" + hexadecimal_number
        elif remainder == 8:
            hexadecimal_number = "8" + hexadecimal_number
        elif remainder == 9:
            hexadecimal_number = "9" + hexadecimal_number
        elif remainder == 10:
            hexadecimal_number = "A" + hexadecimal_number
        elif remainder == 11:
            hexadecimal_number = "B" + hexadecimal_number
        elif remainder == 12:
            hexadecimal_number = "C" + hexadecimal_number
        elif remainder == 13:
            hexadecimal_number = "D" + hexadecimal_number
        elif remainder == 14:
            hexadecimal_number = "E" + hexadecimal_number
        elif remainder == 15:
            hexadecimal_number = "F" + hexadecimal_number

        decimal_number = decimal_number // 16

    return hexadecimal_number

print(decToHex(100));

Decimal To Octal

def decToHex(dec):
    octal = "";
    while(dec != 0):
        octal= str(dec%8) + octal;
        dec = int(dec/8);
    return octal;

print(decToHex(1000));

Octal To Decimal

def octalToDec(octal):
    dec = 0;
    octal = str(octal);
    for i in range(len(octal)):
        dec += int(octal[i])*(8**(len(octal)-1-i));
    return dec;

print(octalToDec(1111));