How Does the = Operator Work with Custom Objects in Python?

Understanding the = Operator in Python

In Python, the = operator is a versatile tool that simplifies code by combining assignment and addition. It is essentially syntactic sugar for the iadd special method. If iadd is not present in a class, add or radd may be used instead.

For example, consider the list object. When you use the = operator on a list, Python iterates over the provided iterable, appending each element to the list. This behavior is similar to the list's extend method.

To illustrate how the iadd method works, let's create a custom class called Adder:

class Adder(object):
    def __init__(self, num=0):
        self.num = num

    def __iadd__(self, other):
        print('in __iadd__', other)
        self.num += other
        return self.num

In this class, the iadd method adds the provided number to the Adder object's num attribute and returns the updated value.

Using the = operator on an Adder object will call the iadd method:

a = Adder(2)
a += 3  # Will print "in __iadd__ 3"
print(a)  # Outputs 5

By customizing the iadd method, you can tailor the addition behavior for your own objects. This adds flexibility and expressiveness to your code.

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