Python __abs__()

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Syntax

object.__abs__()

Python’s object.__abs__() method returns the absolute value of the object and implements the built-in function abs().

The absolute value of any numerical input argument -x or +x is the corresponding positive value +x. However, you can overwrite the default behavior by defining a custom __abs__() method.

We call this a “Dunder Method” for Double Underscore Method”. To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.

Example

In the following example, you create a custom class Data and overwrite the __abs__() method so that it multiplies the attribute self.value with 10.

class Data:

    def __init__(self, value):
        self.value = value
        
    def __abs__(self):
        return self.value * 10


my_value = Data(4.2)
print(abs(my_value))
# 42.0

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

How to Resolve TypeError: bad operand type for abs(): ‘Data’

Consider the following code snippet where you try to call the built-in function abs() on a custom object:

class Data:

    def __init__(self, value):
        self.value = value


my_value = Data(4.2)
print(abs(my_value))

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

Traceback (most recent call last):
  File "C:\Users\xcent\Desktop\code.py", line 8, in <module>
    print(abs(my_value))
TypeError: bad operand type for abs(): 'Data'

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

class Data:

    def __init__(self, value):
        self.value = value
        
    def __abs__(self):
        return self.value * 10


my_value = Data(4.2)
print(abs(my_value))
# 42.0

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