NotImplemented Not implemented marker
Last updated: 2026-09-22
NotImplemented Not implemented marker
NotImplemented is returned by binary dunder methods to signal 'try the reflected operation'.
| Category | Keywords & Statements |
|---|---|
| Kind | Keyword / Statement |
| Python Version | all |
📝 Syntax
NotImplemented▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
False💡 Related Cases
More case studies coming soon — check back later.
❓ FAQ
QWhat is the difference between `NotImplemented` and `NotImplementedError`?
A`NotImplemented` is a singleton object returned by binary-operator methods like `__eq__` or `__add__`, meaning «I do not support this operation, please try the reflected operation». `NotImplementedError` is an exception class meaning «this abstract method is not yet implemented».
QWhat happens if my `__eq__` returns `NotImplemented`?
APython swaps the operands and tries the reflected method of the other side (e.g. `other.__eq__(self)`). If the other side also returns `NotImplemented`, the final result of `==` is `False` (and `!=` is `True`).
QWhen should I return `NotImplemented`?
AWhen implementing binary-operation dunder methods like `__eq__`, `__add__`, `__lt__`, if you encounter an unrecognized type, return `NotImplemented` rather than raising `TypeError`, so Python can try other mechanisms.
