Basic in-place addition
Input
iadd_demo(2, 3)
Output
5
Creates MutableNumber(2), does += 3 (an int). The internal value becomes 5 and that value is returned by the helper function.
Full lesson preview
Support In-Place Addition with __iadd__
Implement in-place addition behavior for a mutable numeric wrapper using __iadd__.
Python practice25 minMagic Methods & Operator OverloadingAdvancedLast updated April 11, 2026
Problem statement
Create a small mutable numeric wrapper class MutableNumber that stores a numeric value. Implement the __iadd__ magic method so that the object supports in-place addition using the '+=' operator. The method should: - Mutate the receiver's stored value by adding the other operand's numeric value. - Support adding an int or float, or another MutableNumber instance. - Return self so chained in-place operations behave correctly. If the other operand type is unsupported, return NotImplemented.
Task
Learn to implement __iadd__ so objects can be updated with the '+=' operator and return themselves, handling different operand types correctly.
Examples
Input format
The test harness will call iadd_demo(a, b) where a is the initial numeric value and b is either a number (int/float) or a MutableNumber instance.
Output format
Return the numeric value stored inside the MutableNumber after performing the in-place addition.
Constraints
- You must implement __iadd__ on the MutableNumber class. - __iadd__ should mutate self.value and return self. - If the other operand is a MutableNumber, use its .value. - For unsupported types, return NotImplemented.
Samples
Sample 1
Input
iadd_demo(10, MutableNumber(5))
Output
15
Adding another MutableNumber adds its value.