It might be easily handled as I guess all arguments are references to python objects, and the regular code for expanding numbers could switch out the reference - but the point remains that proper tail call optimization in python needs to deal with objects as arguments. Come from has no indication on the other side that it will happen. -- Steven Skiena, lru_cache decorator is great for people who are happy to let the language handle the caching of results for them, and often leads to code which is much more concise than the dynamic programming approach. Python doesn't really need it. at the end of a map is as fast as doing a non-tail-recursive map. It’s much easier to understand tail recursion with an actual example followed by an explanation of that example. If you want fib(10000) you need to call fib(1) through fib(9999) first, as if you were implementing a dynamic programming solution. Does it actually "optimize" things and make the function take a constant space as it is calling itself? ;-). This can also be done using trampolines without using try/catch method: Code snippets you won't see if you have JS disabled: I've noticed a shift over the last while how privacy-protective people are becoming "out-group" and a little weird. And on 64 bit architectures address space isn't a problem, but the memory from a temporary large stack can't be re-used without swapping the old stack contents out which is slow. Many problems (actually any problem you can solve with loops,and a lot of those you can’t) can be solved by recursively calling a function until a certain condition is met. Tail recursion is considered a bad practice in Python, since the Python compiler does not handle optimization for tail recursive calls. The original article isn't too bad, but one of the other comments suggests re-writing the contents of the function at run time, which I really don't think is a practical suggestion (think about debugging such a thing). By the way, the first example where it has `return 1` is wrong. The new one gets rid of catching exceptions and is faster. It won't help unless you call it in a specific order e.g., fib(10_000) may produce RecursionError unless you run for n in range(10_000): fib(n). The decorator makes it a non-recursive function with a loop. The idea of function calls is much simpler - no yield magic necessary. Yes! This can be changed by setting the sys.setrecursionlimit(15000) which is faster however, this method consumes more memory. You are simply avoiding a stack overflow which is not the purpose of tail-call optimization. Also avoiding downloading JS libraries bigger than Quake while on the go. TCO can be applied are precisely the ones that are not For example in python you can do: Python's generators are more magic. Flash fully disabled in this day and age? It takes a constant space since it is not even recursive. ... and popped off the stack when the recursion finishes. I do think it's a shame that Python doesn't have general TCO. But some things are so easily expressed as a recursion but require considerable thought to be turned into a loop. You end up with a one sided tree structure that can't be parallel processed. A more accurate statement would be that all recursive programs that are _iterative_ (if they are loops in disguise), can be rewritten in a tail-call form. First, I'm talking about the stack in Scheme (the high level language), since that's what we are talking about here (you gave map as an example); whether there's a C stack used underneath somewhere only matters in this context if its size is tied to the stack size available to Scheme programs. many frameworks do exactly this. Confusing, I know, but stick with me. But it is funny to see technical preferences as a signaling mechanism. For all values of n > 1, that function will return 1, which is clearly not what the author intended. Scheme also did not just introduce tail recursion, but full tail call optimization. > else: return tail_factorial(n-1, accumulator * n), [ed: ah, no. Tail recursion is an important programming concept because it allows us to program recursively, but also because xkcd says it is. TCO, explicit or not, isn't wanted in Python. I'm not sure if there is any advantage when language/compiler does not provide a proper tail recursive optimization. Making the C stack large enough is not solving it on 32 bit architectures with enough physical RAM that you can't/don't want to waste address space. When compiling/transpiling/whatever between languages, I have found that relying on regular procedure calls and TCO is generally a lot simpler than having to force the looping facility of one language into the semantics of another language.
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