I’ve been reading a lot about closures and I think I understand them, but without clouding the picture for myself and others, I am hoping someone can explain closures as succinctly and clearly as possible. I’m looking for a simple explanation that might help me understand where and why I would want to use them.
Closures are an incredibly useful language feature. They let us do clever things that would otherwise take a lot of code, and often enable us to write code that is more elegant and more clear. In Python 2.x, closures variable names cannot be rebound; that is, a function defined inside another lexical scope cannot do something like some_var = 'changed!' for variables outside of its local scope. Can someone explain why that is? There have been situations in which I would like to create a closure that rebinds variables in the outer scope, but it wasn’t possible. I realize that in almost all cases (if not all of them), this behavior can be achieved with classes, but it is often not as clean or as elegant. Why can’t I do it with a closure?
Where X is any programming language (C#, Javascript, Lisp, Perl, Ruby, Scheme, etc) which supports some flavour of closures.
Beazley pg 100 mentions:
There’s a surprise here:
The following test fails:
is it possible to access the python function object attributes from within the function scope?
I’m trying to find a way to make a decorator that does something like injecting a name into the scope of another function (such that the name does not leak outside the decorator’s scope). For example, if I have a function that says to print a variable named var that has not been defined, I would like to define it within a decorator where it is called. Here is an example that breaks:
A 3rd party library we use contains a rather long function that uses a nested function inside it. Our use of that library triggers a bug in that function, and we very much would like to solve that bug.