# Python float() Function

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Python’s built-in `float(value)` function converts the argument `value` to a float number. For example, `float('42')` converts the string value `'42'` into the float number `42.0`.

```>>> float('42')
42.0
>>> float('-42')
-42.0
>>> float('+1.42')
1.42
>>> float('   -11\n')
-11.0
>>> float('10e-3')
0.01
>>> float('+1E6')
1000000.0```

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## Python float() Custom Object

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

```class Car:
def __float__(self):
return -3.21

porsche = Car()
print(float(porsche))
# -3.21
```

In the example, you create a class `Car` and implement the `__init__(self)` method that always returns the float (e.g., `-3.21`). Thus, you can pass a `Car` object `porsche` into the `float()` function and Python doesn’t throw an exception.

Speaking of which…

## Python float() Exception

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

```class Car:
None

porsche = Car()
print(float(porsche))```

This leads to the error message:

```Traceback (most recent call last):
File "C:\Users\finxter\...\code.py", line 6, in <module>
print(float(porsche))
TypeError: float() argument must be a string 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 __float__(self):
return 42.42

porsche = Car()
print(float(porsche))
# 42.42```

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

Lists:

```>>> float([1, 2, 3])
Traceback (most recent call last):
File "<pyshell#28>", line 1, in <module>
float([1, 2, 3])
TypeError: float() argument must be a string or a number, not 'list'```

Sets:

```>>> float({1, 2, 3})
Traceback (most recent call last):
File "<pyshell#29>", line 1, in <module>
float({1, 2, 3})
TypeError: float() argument must be a string or a number, not 'set'```

Dictionaries:

```>>> float({'Alice': 23, 'Bob': 17})
Traceback (most recent call last):
File "<pyshell#30>", line 1, in <module>
float({'Alice': 23, 'Bob': 17})
TypeError: float() argument must be a string or a number, not 'dict'```

Tuples:

```>>> float((1, 2, 3))
Traceback (most recent call last):
File "<pyshell#31>", line 1, in <module>
float((1, 2, 3))
TypeError: float() argument must be a string or a number, not 'tuple'```

## Summary

Python’s built-in `float(value)` function converts the argument `value` to a float number.

For example, `float('42')` converts the string value `'42'` into the float number `42.0`.

```>>> float('42')
42.0```

Want to keep improving your Python skills? Check out our free Python cheat sheets:

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