In this post, we will learn number system conversion in Python using built-in functions with detailed explanations and examples.

There are many built-in functions in Python that help us convert decimal numbers to binary, octal, and hexadecimal numbers, or vice-versa. Let’s learn each of these functions with the help of examples.

## bin() Function

The `bin()` function is used to convert decimal integers into their respective binary representation.

``````num = int(input("Enter a number: "))
binary = bin(num)

print(f"Binary of {num} is : {binary}")``````

Output:

``````Enter a number: 10
Binary of 10 is : 0b1010``````

The first two characters `0b` represent that it is a binary number and the remaining character `1010` is the actual binary representation of the given number.

## oct() function

The `oct()` function is used to convert decimal integers into their respective octal representation.

``````num = int(input("Enter a number: "))
octal = oct(num)

print(f"Octal of {num} is : {octal}")``````

Output:

``````Enter a number: 10
Octal of 10 is : 0o12``````

As we already discussed, the first two characters `0o` represent that it is an octal number, and the remaining `12` is the actual octal representation of given number.

## hex() function

The `hex()` function is used to convert decimal integers into their respective hexadecimal representations.

``````num = int(input("Enter a number: "))

Output:

``````Enter a number: 10
Hexadeciaml of 10 is : 0xa``````

The first two characters `0x` represent that it is a hexadecimal number and the remaining character `a` is the actual hexadecimal representation of the given number.

Now let’s discuss how we can convert any binary, octal, and hexadecimal number into their respective decimal numbers.

## Binary to Decimal Number

We use the `int()` function to convert any binary number into its respective decimal number. There is one attribute of the `int()` function called `base` that helps us convert any number system into its respective decimal number.

If you want to convert a binary number into a decimal number, you can achieve this by simply changing the `base=2` in the `int()` function by default `base` is set to 10. But remember one thing You have to pass a binary number or another number system such as an octal or hexadecimal number in the form of a string otherwise you will get an error.

``````binary = "10"
decimal = int(binary,base=2)

print(f"Decimal of binary number {binary} is: {decimal}")``````

Output:

``Decimal of binary number 10 is: 2``

## Octal to Decimal Number

To convert an octal number to its respective decimal representation, pass the octal number as a string to the `int()` function and set the `base` to 8.

``````octal = "12"
decimal = int(octal,base=8)

print(f"Decimal of octal number {octal} is: {decimal}")``````

Output:

``Decimal of octal number 12 is: 10``

To convert a hexadecimal number to its respective decimal representation, pass the hexadecimal number as a string to the `int()` function and set the `base` to 16.

``````hexadecimal = "a"

``Decimal of hexadecimal number a is: 10`` 