# Python __floor__() Magic Method

## Syntax and Definition

``object.__floor__(self)``

The Python `__floor__()` method implements the behavior of the `math.floor()` function. For example, if you attempt to call `math.floor(x)`, Python will run the `x.__floor__()` method to obtain the return value.

We call this a “Dunder Method” for Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.

## Example

The following code snippet overrides the `__floor__()` dunder method to return the “rounded down” age of a `Person` when you pass an object of type `Person` into the `math.floor()` function:

```import math

class Person:
def __init__(self, age):
self.age = age

def __floor__(self):
floor_value = int(self.age)
return floor_value

alice = Person(42.99999)
print(math.floor(alice))
# 42

bob = Person(42.0)
print(math.floor(bob))
# 42
```

## How to fix “TypeError: must be real number, not XXX”?

Note that without defining the `__floor__()` method, Python would’ve raised a `TypeError`:

```import math

class Person:
def __init__(self, age):
self.age = age

alice = Person(42.99999)
print(math.floor(alice))```

Output:

```Traceback (most recent call last):
File "C:\Users\...\code.py", line 10, in <module>
print(math.floor(alice))
TypeError: must be real number, not Person```

To fix this `TypeError`, simply define the `__floor__()` method as outlined in the first code snippet in this article.

## Background

Let’s first recall what the floor function `⌊⋅⌋` does in mathematical terms. For a real number x, its floor function `⌊x⌋` is just `x` “rounded down”, i.e. the largest integer not exceeding `x`. In particular, if `x` is an integer, then its floor is just itself.

For instance, if `x=9.1`, then the floor of `x` is just `9`. On the other hand, if `x=−9.1`, then the largest integer not exceeding `x` is `−10` (rather than `−9`), so `⌊x⌋=−10`.

If we rephrase this in terms of the integer part `n` of `x`, we get

You can read more in our full guide:

References:

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