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

Let’s dive into the bitwise AND operator first—because if you’ve mastered bitwise AND, understanding the in-place bitwise AND operator is a breeze in the summer.

## Bitwise AND Refresher

Python’s ** bitwise AND** operator

`x & y`

performs *logical AND*on each bit position on the binary representations of integers

`x`

and `y`

. Thus, each output bit is 1 if both input bits at the same position are 1, otherwise, it’s 0. For example, the integer expression 4 & 3 is translated to binaries 0100 & 0011 which results in 0000 because all four input bit positions are different. In this example, you apply the ** bitwise AND **operator to two integers 32 and 16:

>>> 32 & 16 0

The expression `32 & 16`

operates on the bit representations `"010000"`

(decimal 32) and `"001000"`

(decimal 16) and performs ** bitwise AND**. As all i-th bit positions are different, the result is 0:

First Operand `x` | 1 | 0 | 0 | 0 | 0 | 0 |

Second Operand `y` | 0 | 1 | 0 | 0 | 0 | 0 |

`x & y` | 0 | 0 | 0 | 0 | 0 | 0 |

Similarly, let’s have a look at a slightly modified example to showcase the ** bitwise AND **operator:

>>> 31 & 15 15

You can see this in the following visualization:

First Operand `x` | 1 | 1 | 1 | 1 | 1 |

Second Operand `y` | 0 | 1 | 1 | 1 | 1 |

`x & y` | 0 | 1 | 1 | 1 | 1 |

The decimal representation of the bit sequence `"01111"`

is 15.

**Related Article: **Python Bitwise AND Operator Deep Dive

## Python In-Place Bitwise AND Magic Method

To use the in-place bitwise AND operator `&=`

on custom objects, define the `__iand__()`

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

and `other`

, updates the first argument `self`

with the result of the operation, and returns the updated object.

In the following code, you calculate the result on two `Data`

objects:

class Data: def __init__(self, data): self.data = data def __iand__(self, other): self.data &= other.data return self x = Data(1) # b001 y = Data(3) # b011 x &= y # b001 print(x.data) # 1

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

## 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.

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