Table of Contents

## Syntax

object.__ror__(self, other)

The Python `__ror__()`

method implements the reverse Bitwise OR | operation with reflected, swapped operands. So, when you call `x | y`

, Python attempts to call `x.__or__(y)`

. If the method is not implemented, Python attempts to call `__ror__`

on the right operand and if this isn’t implemented either, it raises a `TypeError`

.

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.

## Background Bitwise OR |

Python’s bitwise OR `x | y`

performs *logical OR* on each bit position on the binary representations of integers `x`

and `y`

.

Each output bit evaluates to 1 *if and only if *at least one of the two input bits at the same position are 1.

For example, the integer expression `4 | 3`

is translated to the binary operation `0100 | 0011`

which results in `0111`

because for the last three positions at least one bit is 1.

In this example, you apply the ** bitwise OR **operator to two integers 32 and 16:

>>> 32 | 16 48

The expression `32 | 16`

operates on the bit representations `"010000"`

(decimal 32) and `"001000"`

(decimal 16) and performs ** bitwise OR**. Each

`"1"`

position propagates remains in the result `"110000"`

(decimal 48):First Operand `x` | 1 | 0 | 0 | 0 | 0 | 0 |

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

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

To understand this operation in detail, feel free to read over our tutorial or watch the following video:

## Python __or__ vs __ror__

Say, you want to calculate the `|`

operation on two custom objects `x`

and `y`

:

print(x | y)

Python first tries to call the left object’s `__or__()`

method `x.__or__(y)`

. But this may fail for two reasons:

- The method
`x.__or__()`

is not implemented in the first place, or - The method
`x.__`

is implemented but returns a`or`

__()`NotImplemented`

value indicating that the data types are incompatible.

If this fails, Python tries to fix it by calling the `y.__ror__()`

for *reverse bitwise OR *on the right operand `y`

.

If the reverse bitwise OR method is implemented, Python knows that it doesn’t run into a potential problem of a non-commutative operation. If it would just execute `y.__or__(x)`

instead of `x.__or__(y)`

, the result would be wrong because the operation may be non-commutative when defined as a custom operation. That’s why `y.__ror__(x)`

is needed.

So, the difference between `x.__or__(y)`

and `x.__ror__(y)`

is that the former calculates `x | y`

whereas the latter calculates `y | x`

— both calling the respective method defined on the object `x`

.

You can see this in effect here where we attempt to call the operation on the left operand `x`

—but as it’s not implemented, Python simply calls the reverse operation on the right operand `y`

.

class Data_1: pass class Data_2: def __ror__(self, other): return 'called reverse bitwise OR' x = Data_1() y = Data_2() print(x | y) # called reverse bitwise OR

**References:**

## Where to Go From Here?

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