High Dunder Methods Question 196 of 228

How do reflected numeric dunders such as radd get chosen?

Python & Django · Speak this in 60–90 seconds · Faridabad & Delhi NCR

IdeaDunder Methods

HowWhat happens inside

Why they askShows real use

For a + b, Python tries a.__add__(b)

Why interviewers care about Dunder Methods:

This is a process

question about Dunder Methods.

Panels listen for order,

trade-offs, and what you would actually do on a Python project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before you speak the answer, walk the interviewer through these steps:

1
For a + b,
Python tries a.__add__(b)
2
if that returns NotImplemented,
it tries b.__radd__(a).
3
Subclass instances may skip
the left op so the subclass can coerce types.
4
Returning NotImplemented rather than
raising TypeError is what makes mixed-type arithmetic work.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“Subclass instances may skip the left op so the subclass can coerce types.”

Break into beats

Subclassinstancesmayskiptheleft

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

For a + b, Python tries a.__add__(b) if that returns NotImplemented, it tries b.__radd__(a).

How do reflected numeric dunders such as __radd__ get chosen?