# Python int() Function

Python’s built-in `int(value)` function converts the argument `value` to an integer number. For example, `int('42')` converts the string value `'42'` into the integer number `42`. The `int()` function on a float argument rounds down to the closest integer.

```Input : `int('42')`
Output : `42`

Input : `int('-42')`
Output : `-42`

Input : `int(0)`
Output : `0`

Input : `int(3.41)`
Output : `3`

Input : `int(3.51)`
Output : `3`

Input : `int('101', base=2)`
Output : `5````

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## Python int() Rounding

The `int(x)` function on a float value `x` rounds down to the closest integer.

```>>> int(3.41)
3
>>> int(3.51)
3
>>> int(3.9999)
3```

## Python int() Custom Object

To allow a custom object as an input to the `int(object)` function, the object must implement the `__int__(self)` dunder method that returns an integer value. In fact, the `int(object)` built-in function is semantically equivalent to the `object.__int__()` function call.

```class Car:
def __int__(self):
return -1

porsche = Car()
print(int(porsche))
# -1```

In the example, you create a class `Car` and implement the `__init__(self)` method that always returns the integer -1. Thus, you can pass a `Car` object `porsche` into the `int()` function and Python doesn’t throw an exception.

Speaking of which…

## Python int() Exception

If you pass an object into the `int()` function that doesn’t overwrite the `__int__()` method—for example, a list, tuple, or set—Python throws a TypeError:

```class Car:
None

porsche = Car()
print(int(porsche))```

This leads to the error message:

```Traceback (most recent call last):
File "C:\Users\...\code.py", line 6, in <module>
print(int(porsche))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'Car'```

To fix the error, either pass an object that is convertible to an integer or implement your own `__int__(self)` method as shown previously:

```class Car:
def __int__(self):
return -1

porsche = Car()
print(int(porsche))
# -1```

Note that the same `TypeError` appears if you try to convert lists, sets, dictionaries, or tuples to integer values using the `int()` function.

Lists:

```>>> int([1, 2, 3])
Traceback (most recent call last):
File "<pyshell#10>", line 1, in <module>
int([1, 2, 3])
TypeError: int() argument must be a string, a bytes-like object or a number, not 'list'
```

Sets:

```>>> int({1, 2, 3})
Traceback (most recent call last):
File "<pyshell#11>", line 1, in <module>
int({1, 2, 3})
TypeError: int() argument must be a string, a bytes-like object or a number, not 'set'
```

Dictionaries:

```>>> int({'Alice': 23, 'Bob': 17})
Traceback (most recent call last):
File "<pyshell#12>", line 1, in <module>
int({'Alice': 23, 'Bob': 17})
TypeError: int() argument must be a string, a bytes-like object or a number, not 'dict'
```

Tuples:

```>>> int((1, 2, 3))
Traceback (most recent call last):
File "<pyshell#13>", line 1, in <module>
int((1, 2, 3))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'tuple'```

## Python int() base Argument

The `int(value, base=10)` function has an optional argument `base` that allows you to define the base of the numerical system in the `value` argument. If you set the base, the input must be a string. The `base` argument determines how the string argument is interpreted. For example, `int('10', base=2)` converts the string `'10'` —representing a binary number—to the integer 2.

```>>> int('10', base=2)
2```

## Summary

Python’s built-in `int(value)` function converts the argument `value` to an integer number.

For example, `int('42')` converts the string value `'42'` into the integer number `42`.

```>>> int('42')
42```

The `int()` function on a float argument rounds down to the closest integer.

```>>> int(3.99)
3```

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