Python reverse() vs [::-1] slice performance
Question:
Python provides two ways to reverse a list:
List slicing notation
['a','b','c'][::-1] # ['c','b','a']
Built-in reversed() function
reversed(['a','b','c']) # ['c','b','a']
Are there any relevant differences in implementation/performance, or scenarios when one is preferred over the other?
Answers:
The slicing operator constructs a new list in memory, which has implications on both memory and runtime.
reversed, on the other hand, returns an iterator which simply yields items one after another from the original list in reversed order. It does not allocate any additional memory.
So if all you’re doing is iterating over the list in reverse and there’s no need to construct a new (for example if you need to mutate it), then I’d say go for reversed.
Python provides two ways to reverse a list:
List slicing notation
['a','b','c'][::-1] # ['c','b','a']
Built-in reversed() function
reversed(['a','b','c']) # ['c','b','a']
Are there any relevant differences in implementation/performance, or scenarios when one is preferred over the other?
The slicing operator constructs a new list in memory, which has implications on both memory and runtime.
reversed, on the other hand, returns an iterator which simply yields items one after another from the original list in reversed order. It does not allocate any additional memory.
So if all you’re doing is iterating over the list in reverse and there’s no need to construct a new (for example if you need to mutate it), then I’d say go for reversed.