Use the tail_recursive decorator to simply define tail recursive functions.. #!/usr/bin/env python2.4 # This program shows off a python decorator which implements tail call optimization. The module allows a coder to write tail-recursive functions as well as using continuation-passing style in his/her code without having the size of the execution stack increasing. For runs under the limit anyway, it'd be interesting to see whether it's any faster. If you are encountering maximum recursion depth errors or out-of-memory crashes tail recursion can be a helpful strategy.. 2.969 -- undecorated 3.312 -- with Cython decorator + 11% 7.437 -- with Python decorator + 150% These are about the same proportions as for factorial example. pip install tail-recursive. Tail-call optimization. Python has a small limit to how many recursive calls can be made (typically ~1000). We need Python to discard the previous frame when a tail-recursive function calls itself. It takes a constant space since it is not even recursive. However, as the output shows Python still executes it like a recursive function and keeps all the frames. The reference Python implementation (CPython) does not implement tail-call optimization, so running the above code will hit the recursion limit and throw an exception. In all four cases I get the same results, so it does work with both # Tail Recursion Optimization Through Stack Introspection This is a quite good result and I don’t shy away from recommending it. It # does this by throwing an exception if it is it's own grandparent, and catching such # exceptions to recall the stack. tail-recursion? It'll effectively side-steps the recursion limit in Python. Example from tail_recursive import tail_recursive # Pick a larger value if n is below your system's recursion limit. Here we have seen what is tail recursion & how to let Python eliminate tail calls by using the tail_recursive decorator to simply define tail recursive functions. It trades function call overhead for exception handling overhead. Tail-call optimization is a method which allows infinite recursion of tail- recursive functions to occur without stack overflow. Installation. And, although, Python's "hardware" won't allow it, its introspective nature already allow us to do so, via decorators. Pure python tail-call optimization? Tail Calls. Tail recursion is considered a bad practice in Python, since the Python compiler does not handle optimization for tail recursive calls. Basic Usage. From the google page do "define: tail recursion" I tried the tail_recursion decorator from the cookbook-recipe with both definitions of factorial, and I tried both definitions of the factorial function with and without tail_recursion decorator. here is the idea: You wrap the too-be-tail-recursive function in an object that, when called, takes note of the thread it's running, the depth of the call, and the parameters used. Instead, we can also solve the Tail Recursion problem using stack introspection. The decorator makes it a non-recursive function with a loop. Consider the factorial function below: When we make the call fac(3), two recursive calls are made: fac(2, 3) and fac(1, 6).The last call returns 6, then fac(2, 3) returns 6, and finally the original call returns 6.I would recommend looking at the execution in Python Tutor: My conclusion is that one can expect about 10% performance penalty for Cythons tail_recursive decorator. 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