# bin() function in Python

## Introduction

The `bin()` function converts and returns the binary equivalent string of a given integer. If the parameter isn't an integer, it has to implement `__index__()` method to return an integer.

The syntax of `bin()` method is:

```python
bin(num)
```

where num is an integer number whose binary equivalent is to be calculated.

Note: In Python, a binary number is represented as a string prefixed with **0b**.

## Case 1: Integer to Binary

```python
num = 3
print(bin(num))
```

Output:

```bash
0b11
```

## Case 2: Object to Binary

In the case of Objects, we need to implement the `__index__()` method to get the binary equivalent string for an object.

```python
class Money:
    ten_rupee_note = 3
    fifty_rupee_note = 5
    hundred_rupee_note = 7

    def __index__(self):
        return (10*self.ten_rupee_note) + (50*self.fifty_rupee_note) + (100*self.hundred_rupee_note)


money = Money()
print(f"Total Money: {money.__index__()}")
print(f"Total Money in Binary: {bin(money)}")

```

Output:

```bash
Total Money: 980
Total Money in Binary: 0b1111010100

```

Here, we've created a ***Money*** class with three attributes - `ten_rupee_note`, `fifty_rupee_note`, and `hundred_rupee_note`. The `__index__()` method returns the total money, i.e. the sum of notes multiplied with their respective valuation. We then pass an object of the ***Money*** class to the binary function which returns the binary equivalent string of the integer returned by the `__index__()` method.

## Case 3: Raises Exception

```python
class Money:
    ten_rupee_note = 3
    fifty_rupee_note = 5
    hundred_rupee_note = 7


money = Money()
print(f"Total Money in Binary: {bin(money)}")

```

In the previous example, if we don't implement the `__index__()`method, we'll get a TypeError.

Output:

```bash
Traceback (most recent call last):
  File "D:\Quarantine\Test\Blog-Codes\Built-Ins\bin\error.py", line 8, in <module>
    print(f"Total Money in Binary: {bin(money)}")
TypeError: 'Money' object cannot be interpreted as an integer
```

## Conclusion

In this part, we learned about the Python `bin()` function with the help of examples. You can check out [this tool](https://www.calculator.net/binary-calculator.html) to convert to binary.