4 ms·
For the basic sequence types (list, tuple, and range), len is definitely not expensive to compute. For custom types, it will depend on your implementation of __
by fantod 6y ago
For the basic sequence types (list, tuple, and range), len is definitely not expensive to compute. For custom types, it will depend on your implementation of __len__ (but then, computation of bool(...) will also depend on your implementation of __bool__).
- orf 6y agoYes, len() with the basic types are not expensive, and it can vary based on the container implementation, but that’s not really the point. The reason you should use “if x” is the same reason you should use “if x not in y” rather than “if not x in y”. It better expresses the semantics of your operation with the side effect that it may be faster.
- fantod 6y agoOh yeah, totally agree that it's idiomatic and (in my opinion) cleaner.