# Python __rshift__() Magic Method

## Syntax

`object.__rshift__(self, other)`

The Python `__rshift__()` method implements the built-in `>>` operation. So, when you cal `x >> y`, Python attempts to call `x.__rshift__(y)`. If the method is not implemented, Python first attempts to call `__rrshift__` 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 rshift()

The Python bitwise right-shift operator `x >> n` shifts the binary representation of integer `x` by `n` positions to the right.

It inserts a `0` bit on the left and removes the right-most bit. For example, if you right-shift the binary representation `0101` by one position, you’d obtain `0010`. Semantically, the bitwise right-shift operator is the same as performing integer division by `2**n`.

```print(8 >> 1)
# 4

print(8 >> 2)
# 2

print(-3 >> 1)
# -2```

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

## Example Custom __rshift__()

In the following example, you create a custom class `Data` and overwrite the `__rshift__()` method so that it returns a dummy string when trying to calculate the bitwise right-shift operation.

```class Data:

def __rshift__(self, other):
return '... my result of rshift...'

a = Data()
b = Data()

print(a >> b)
# ... my result of rshift...
```

If you hadn’t defined the `__rshift__()` method, Python would’ve raised a `TypeError`.

## TypeError: unsupported operand type(s) for >>

Consider the following code snippet where you try to calculate the right-shift operation on custom objects without defining the dunder method `__rshift__()`:

```class Data:
pass

a = Data()
b = Data()

print(a >> b)```

Running this leads to the following error message on my computer:

```Traceback (most recent call last):
File "C:UsersxcentDesktopcode.py", line 8, in <module>
print(a >> b)
TypeError: unsupported operand type(s) for >>: 'Data' and 'Data'```

The reason for this error is that the `__rshift__()` method has never been defined—and it is not defined for a custom object by default. So, to resolve the `TypeError: unsupported operand type(s) for >>`, you need to provide the `__rshift__(self, other)` method in your class definition as shown previously:

```class Data:

def __rshift__(self, other):
return '... my result of rshift...'```

Of course, you’d use another return value in practice as explained in the “Background rshift()” section.

## Python __rshift__ vs __rrshift__

Say, you want to calculate the right-shift operation on two custom objects `x` and `y`:

`print(x >> y)`

Python first tries to call the left object’s `__rshift__()` method `x.__rshift__(y)`. But this may fail for two reasons:

1. The method `x.__rshift__()` is not implemented in the first place, or
2. The method `x.__rshift__()` is implemented but returns a `NotImplemented` value indicating that the data types are incompatible.

If this fails, Python tries to fix it by calling the `y.__rrshift__()` for reverse right-shift on the right operand `y`. Not that this is not the same as left-shift, it just means that the right-shift operation is called on the second operand `y`.

If the reverse right-shift 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.__rshift__(x)` instead of `x.__rshift__(y)`, the result would be wrong because the operation is non-commutative. That’s why `y.__rrshift__(x)` is needed.

So, the difference between `x.__rshift__(y)` and `x.__rrshift__(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 __rrshift__(self, other):
return 'called reverse rshift'

x = Data_1()
y = Data_2()

print(x >> y)
# called reverse rshift
```

References:

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