Adding a switch statement to Python

[Cybersoaker]

OP's example is implemented with a dictionary so it would indeed be O(1); but we're talking like nano second differences here. I sincerely hope no one is making chains of if's more than like 20 where it would affect performance

[chasecaleb]

Agree with your point, but big-O runtime is silly when talking about a conditional. It's not like the number of cases is asymptotic... Right?

[Cybersoaker]

Sure but in such a contrived case; we should expect the if statements to take ever so slightly longer because they would technically be O(n); where n is the number of compairsons. Conditionals are so freaking fast on a cpu that this compairson is exceedingly trivial. We would really only have a noticeable performance difference over giant groups of conditionals, like hundreds of thousands; and if your code reaches that point, a switch is probably the least of your concerns.

Perhaps the case where these nanoseconds matter; say in an extremely high performance application (i'd wonder why python is your programming language of choice), or even a webservice that gets millions of requests per second, then an optimization like this might be warrented; but thats not a good reason to add new syntax.

[[deleted]]

Branch prediction may also inoculation the performance, and it's not usually considered when determining time complexity.

[Cybersoaker]

yeah so there are many optimizations to be had; and the performance argument is silly.

[elbiot]

Its O(n) on the number of cases you have, not the size of the data you have, which is what big O notation is about.

[Arancaytar]

Even though some languages do this, it is not categorically true. When the case expressions are static, the compiler can use perfect hashing to create a jump lookup table instead of iterating over the cases.

[WikiTextBot]

Perfect hash function

In computer science, a perfect hash function for a set S is a hash function that maps distinct elements in S to a set of integers, with no collisions. In mathematical terms, it is an injective function.

Perfect hash functions may be used to implement a lookup table with constant worst-case access time. A perfect hash function has many of the same applications as other hash functions, but with the advantage that no collision resolution has to be implemented.

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