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` |

You can watch me go over all of these operators in the following video:

We’ll rush over all in-place operators one-by-one next!

Table of Contents

## Python In-Place Addition

Python provides the operator `x += y`

to add two objects in-place by calculating the sum `x + y`

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

. You can set up the in-place addition behavior for your own class by overriding the magic “dunder” method `__iadd__(self, other)`

in your class definition.

>>> x = 1 >>> x += 2 >>> x 3

The expression `x += y`

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

:

>>> x = 1 >>> x = x + 2 >>> x 3

**Related Tutorial:** Python In-Place Addition

## Python In-Place Subtraction

Python provides the operator `x -= y`

to subtract two objects in-place by calculating the difference `x - y`

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

. You can set up the in-place subtraction behavior for your own class by overriding the magic “dunder” method `__isub__(self, other)`

in your class definition.

>>> x = 3 >>> x -= 2 >>> x 1

The expression `x -= y`

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

:

>>> x = 3 >>> x = x - 2 >>> x 1

**Related Tutorial:** Python In-Place Subtraction

## Python In-Place Multiplication

Python provides the operator `x *= y`

to multiply two objects in-place by calculating the product `x * y`

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

. You can set up the in-place multiplication behavior for your own class by overriding the magic “dunder” method `__imul__(self, other)`

in your class definition.

>>> x = 2 >>> x *= 3 >>> x 6

The expression `x *= y`

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

:

>>> x = 2 >>> x = x * 3 >>> x 6

**Related Tutorial:** Python In-Place Multiplication

## Python In-Place Division

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

**Related Tutorial:** Python In-Place Division

## Python In-Place Modulo

Python provides the operator `x %= y`

to calculate the modulo operation `x % y`

, and assign the result in-place to the first operands variable `x`

. You can set up the in-place modulo behavior for your own class by overriding the magic “dunder” method `__imod__(self, other)`

in your class definition.

>>> x = 9 >>> x %= 4 >>> x 1

The expression `x %= y`

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

:

>>> x = 9 >>> x = x % 4 >>> x 1

**Related Tutorial:** Python In-Place Modulo

## Python In-Place Integer Division

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

**Related Tutorial:** Python In-Place Integer Division

## Python In-Place Exponentiation

Python provides the in-place exponentiation operator `x **= y`

that raises `x`

to the power of `y`

using `x ** y`

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

. You can set up the in-place exponentiation behavior for your own class by overriding the magic “dunder” method `__ipow__(self, other)`

in your class definition.

>>> x = 2 >>> x **= 3 >>> x 8

The expression `x **= y`

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

:

>>> x = 2 >>> x = x ** 3 >>> x 8

**Related Tutorial:** Python In-Place Exponentiation

## Python In-Place Bitwise AND

Python’s in-place bitwise AND operator `x &= y`

calcualtes bitwise-and `x & y`

and assigns the result to the first operand `x`

. To set it up for your own class, override the magic “dunder” method `__iand__(self, other)`

in your class definition.

>>> x = 1 >>> x &= 2 >>> x 0

The expression `x &= y`

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

:

>>> x = 1 >>> x = x & 2 >>> x 3

**Related Tutorial:** Python In-Place Bitwise AND

## Python In-Place Bitwise OR

Python’s `A |= B`

applies the `|`

operator in place. Thus, it is semantically identical to the longer-form version `A = A | B`

of first performing the operation `A | B`

and then assigning the result to the variable `A`

.

The following minimal example creates two Boolean variables A and B and performs the in-place `B |= A`

operation to perform a logical OR operation `B | A`

and assigning the result to the first operand `B`

that becomes `True`

:

>>> A = True >>> B = False >>> B |= A >>> B True

In this example, you’ve seen this in-place operation on Boolean operands. But the `|`

operator is overloaded in Python. The three most frequent use cases for the `|`

and `|=`

operators are the following:

- Python
**Sets**: set union operator - Python
**Dictionaries**: dictionary update operator - Python
**Booleans**: logical OR operator

**Related Tutorial:** Python In-Place Bitwise OR

## Python In-Place Bitwise XOR

Python’s in-place bitwise XOR operator `x ^= y`

calcualtes bitwise XOR `x `

and assigns the result to the first operand `^`

y`x`

. To set this up for your own class, override the magic “dunder” method `__ixor__(self, other)`

in your class definition.

>>> x = 1 >>> x ^= 2 >>> x 3

The expression `x `

is syntactical sugar for the longer-form `^`

= y`x = x `

:`^`

y

>>> x = 1 >>> x = x ^ 2 >>> x 3

**Related Tutorial:** Python In-Place Bitwise XOR

## Python In-Place Bitwise Right-Shift

Python’s *in-place bitwise right-shift operator*`x >>= y`

calculates the right-shift operation `x >> y`

, and assigns the result to the first operands variable name `x`

. You can set up the in-place right-shift behavior in your own class by overriding the magic “dunder” method `__irshift__(self, other)`

in your class definition.

>>> x = 8 >>> x >>= 2 >>> x 2

The expression `x >>= y`

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

:

>>> x = 8 >>> x = x >> 2 >>> x 2

**Related Tutorial:** Python In-Place Bitwise Right-Shift

## Python In-Place Bitwise Left-Shift

Python’s *in-place bitwise left-shift operator*`x <<= y`

calculates the left-shift operation `x << y`

, and assigns the result to the first operands variable name `x`

. You can set up the in-place left-shift behavior in your own class by overriding the magic “dunder” method `__ilshift__(self, other)`

in your class definition.

>>> x = 8 >>> x <<= 2 >>> x 32

The expression `x <<= y`

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

:

>>> x = 8 >>> x = x << 2 >>> x 32

**Related Tutorial:** Python In-Place Bitwise Left-Shift

## Python In-Place Magic Methods

The following table provides the names of the magic methods you need to define to enable in-place operators on your custom class:

Method Name | Description |
---|---|

`__iadd__(self, other)` | In-place addition |

`__isub__(self, other)` | In-place subtraction |

`__imul__(self, other)` | In-place multiplication |

`__truediv__(self, other)` | In-place and normal division |

`__imod__(self, other)` | In-place modulo |

`__floordiv__(self, other)` | In-place and normal integer division |

`__ipow__(self, other)` | In-place exponentiation |

`__iand__(self, other)` | In-place bitwise AND |

`__ior__(self, other)` | In-place bitwise OR |

`__ixor__(self, other)` | In-place bitwise XOR |

`__irshift__(self, other)` | In-place right-shift |

`__ilshift__(self, other)` | In-place left-shift |

In the following code example, we create a custom class `Data`

and define our “magic” double-underscore methods so that we can perform in-place computations on objects of this class.

class Data: def __init__(self, data): self.data = data def __iadd__(self, other): self.data += other.data return self def __isub__(self, other): self.data -= other.data return self def __imul__(self, other): self.data *= other.data return self def __truediv__(self, other): self.data /= other.data return self def __imod__(self, other): self.data %= other.data return self def __floordiv__(self, other): self.data //= other.data return self def __ipow__(self, other): self.data **= other.data return self def __iand__(self, other): self.data &= other.data return self def __ior__(self, other): self.data |= other.data return self def __ixor__(self, other): self.data ^= other.data return self def __irshift__(self, other): self.data >>= other.data return self def __ilshift__(self, other): self.data <<= other.data return self

Let’s try these out!

# In-Place Addition x = Data(3) y = Data(2) x += y print(x.data) # 5 # In-Place Subtraction x = Data(3) y = Data(2) x -= y print(x.data) # 1 # In-Place Multiplication x = Data(3) y = Data(2) x *= y print(x.data) # 6 # In-Place Division x = Data(3) y = Data(2) x /= y print(x.data) # 1.5 # In-Place Modulo x = Data(3) y = Data(2) x %= y print(x.data) # 1 # In-Place Integer Division x = Data(3) y = Data(2) x //= y print(x.data) # 1 # In-Place Power x = Data(3) y = Data(2) x **= y print(x.data) # 9 # In-Place Bitwise AND x = Data(3) y = Data(2) x &= y print(x.data) # 2 # In-Place Bitwise OR x = Data(3) y = Data(2) x |= y print(x.data) # 3 # In-Place Bitwise XOR x = Data(3) y = Data(2) x ^= y print(x.data) # 1 # In-Place Bitwise Right-Shift x = Data(3) y = Data(2) x >>= y print(x.data) # 0 # In-Place Bitwise Left-Shift x = Data(3) y = Data(2) x <<= y print(x.data) # 12

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. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.

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