memoization

In Java, explicitly declared Strings are interned by the JVM, so that subsequent declarations of the same String results in two pointers to the same String instance, rather than two separate (but identical) Strings. For example: public String baz() { String a = "astring"; return a; } public String bar() { String b = "astring" return b; } public void main() { String a = baz() String b = bar() assert(a == b) // passes } My question is, does CPython (or any other Python runtime) do the same thing for strings? For example, if I have some class: class example(): def __init__(): self._inst =

I'm writing some moderately performance critical code in numpy. This code will be in the inner most loop, of a computation that's run time is measured in hours. A quick calculation suggest that this code will be executed up something like 10^12 times, in some variations of the calculation. So the function is to calculate sigmoid(X) and another to calculate its derivative (gradient). Sigmoid has the property that for y=sigmoid(x), dy/dx= y(1-y) In python for numpy this looks like: sigmoid = vectorize(lambda(x): 1.0/(1.0+exp(-x))) grad_sigmoid = vectorize(lambda (x): sigmoid(x)*(1-sigmoid(x)))

Each time a function is called, if it's result for a given set of argument values is not yet memoized I'd like to put the result into an in-memory table. One column is meant to store a result, others to store arguments values. How do I best implement this? Arguments are of diverse types, including some enums. In C# I'd generally use DataTable. Is there an equivalent in Scala? Aaron Novstrup You could use a mutable.Map[TupleN[A1, A2, ..., AN], R] , or if memory is a concern, a WeakHashMap [1]. The definitions below (built on the memoization code from michid's blog ) allow you to easily memoize

I see that python 3.2 has memoization as a decorator in functools library. http://docs.python.org/py3k/library/functools.html#functools.lru_cache Unfortunately it is not yet backported to 2.7. Is there any specific reason as why it is not available in 2.7? Is there any 3rd party library providing the same feature or should I write my own? Paolo Moretti Is there any specific reason as why it is not available in 2.7? @Nirk has already provided the reason: unfortunately, the 2.x line only receive bugfixes, and new features are developed for 3.x only. Is there any 3rd party library providing the

Looking for a way to implement a universal generic memoization function which will take a function and return the memoized version of the same? Looking for something like @memo (from Norving's site)decorator in python. def memo(f): table = {} def fmemo(*args): if args not in table: table[args] = f(*args) return table[args] fmemo.memo = table return fmemo Going more general, is there a way to express generic and reusable decorators in C++, possibly using the new features of C++11? A compact one returning a lambda: template <typename R, typename... Args> std::function<R (Args...)> memo(R (*fn)