Python’s in-place 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 division for your own class by overriding the magic “dunder” method __truediv__(self, other)
in your class definition.
>>> x = 4 >>> x /= 2 >>> x 2
The expression x /= y
is syntactical sugar for the longer-form x = x / y
:
>>> x = 4 >>> 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 mathematical division of both operands in the left-hand operands’ variable name.
>>> x = 42 >>> x /= 2 >>> x 21
Float Example
If at least one of the operands is a float value, the result is also a float—float is infectious!
>>> x = 42 >>> x /= 2.0 >>> x 21.0
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#2>", line 1, in <module> x /= 3 TypeError: unsupported operand type(s) for /=: 'list' and 'int'
The result of incompatible division is a TypeError
. You can fix it by using only compatible data types for the in-place division operation.
Can you use the division operator on custom objects? Yes!
Python In-Place Division Magic Method
To use the in-place division operator /=
on custom objects, you need to define the __truediv__()
method (“dunder method”, “magic method”) that takes two arguments self
and other
, updates the first argument self
with the result of the division, and returns the updated object.
In the following code, you divide two Data
objects together by combining their contents:
class Data: def __init__(self, data): self.data = data def __truediv__(self, other): self.data /= other.data return self x = Data(42) y = Data(2) x /= y print(x.data) # 21
You can see that the content of the first operand is updated as a result of the in-place division operation.
Note that if you want to override in-place integer division, you need to define the __floordiv__(self, other)
method in your class definition.
Here’s an analogous example:
class Data: def __init__(self, data): self.data = data def __floordiv__(self, other): self.data //= other.data return self x = Data(42.99) y = Data(2.1) x //= y print(x.data) # 20.0
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 |

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