Python’s in-place integer division operator `x //= y`

divides two objects in-place by calculating `x // y`

and assigning the result to the first operands variable name `x`

. Set up in-place integer (or floor) division for your own class by overriding the magic “dunder” method `__floordiv__(self, other)`

in your class definition.

>>> x = 5 >>> x //= 2 >>> x 2

The expression `x /= y`

is syntactical sugar for the longer-form `x = x / y`

:

>>> x = 5 >>> x = x // 2 >>> x 2

Let’s explore some examples on different data types of the operands.

## Integer Example

The `//=`

operator on integer operands stores the result of the mathematical *floor division* of both operands in the left-hand operands’ variable.

>>> x = 9 >>> x //= 2 >>> x 4

## Float Example

If at least one of the operands is a float value, the result is also a float—float is infectious!

>>> x = 9.0 >>> x //= 2 >>> x 4.0

## Incompatible Data Type

What if two operands have an incompatible data type—unlike floats and integers? For example, if you try to divide a list by an integer variable?

>>> x = [1, 2, 3] >>> x //= 3 Traceback (most recent call last): File "<pyshell#30>", line 1, in <module> x //= 3 TypeError: unsupported operand type(s) for //=: 'list' and 'int'

The result of incompatible division is a `TypeError: unsupported operand type(s)`

. You can fix it by using only compatible data types for the in-place integer division operation.

Can you use the division operator on custom objects? Yes!

## Python In-Place Floor Division Magic Method

To use the in-place division operator `//=`

on custom objects, you need to define the `__floordiv__()`

method (*“dunder method”, “magic method”*) that takes two arguments `self`

and `other`

, updates the first argument `self`

with the result of the integer division, and returns the updated object.

In the following code, you divide two `Data`

objects using integer division on their contents contents:

class Data: def __init__(self, data): self.data = data def __floordiv__(self, other): self.data //= other.data return self x = Data(9) y = Data(2) x //= y print(x.data) # 4

You can see that the content of the first operand is updated as a result of the in-place integer division operation.

Note that if you want to override ** in-place division** rather than

**, you need to define the**

*in-place integer division*`__truediv__(self, other)`

method in your class.Here’s an analogous example:

class Data: def __init__(self, data): self.data = data def __truediv__(self, other): self.data /= other.data return self x = Data(9) y = Data(2) x /= y print(x.data) # 4.5

Now Python internally performs the true division `9 / 2 == 4.5`

and not the integer division `9 // 2 == 4`

.

## Python In-Place Operators

In-place assignment operators (also called *compound* assignment operators) perform an operation in-place on a variable provided as first operand. They overwrite the value of the first operand variable with the result of the operation when performing the operator without assignment. For example, `x += 3`

is the same as `x = x + 3`

of first calculating the result of `x +3`

and then assigning it to the variable x.

Operator | Name | Short Example | Equivalent Long Example |
---|---|---|---|

`=` | In-place Assignment | `x = 3` | |

`+=` | In-place Addition | `x += 3` | `x = x + 3` |

`-=` | In-place Subtraction | `x -= 3` | `x = x - 3` |

`*=` | In-place Multiplication | `x *= 3` | `x = x * 3` |

`/=` | In-place Division | `x /= 3` | `x = x / 3` |

`%=` | In-place Modulo | `x %= 3` | `x = x % 3` |

`//=` | In-place Integer Division | `x //= 3` | `x = x // 3` |

`**=` | In-place Power | `x **= 3` | `x = x ** 3` |

`&=` | In-place Bitwise And | `x &= 3` | `x = x & 3` |

`|=` | In-place Bitwise Or | `x |= 3` | `x = x | 3` |

`^=` | In-place Bitwise XOR | `x ^= 3` | `x = x ^ 3` |

`>>=` | In-place Bitwise Shift Right | `x >>= 3` | `x = x >> 3` |

<<= | In-place Bitwise Shift Left | `x <<= 5` | `x = x << 5` |

While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.

To help students reach higher levels of Python success, he founded the programming education website Finxter.com that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.

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