I have an article on this very topic. (It has lots of examples.) In essence, a closure is a block of code which can be executed at a later time, but which maintains the environment in which it was first created – i.e. it can still use the local variables etc of the method which … Read more
Are you talking about lambda expressions? Like lambda x: x**2 + 2*x – 5 Those things are actually quite useful. Python supports a style of programming called functional programming where you can pass functions to other functions to do stuff. Example: mult3 = filter(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, … Read more
The nested function looks up variables from the parent scope when executed, not when defined. The function body is compiled, and the ‘free’ variables (not defined in the function itself by assignment), are verified, then bound as closure cells to the function, with the code using an index to reference each cell. pet_function thus has … Read more
It’s all about variable scoping. Variables declared in the self executing function are, by default, only available to code within the self executing function. This allows code to be written without concern of how variables are named in other blocks of JavaScript code. For example, as mentioned in a comment by Alexander: (function() { var … Read more
Python doesn’t have variable declarations, so it has to figure out the scope of variables itself. It does so by a simple rule: If there is an assignment to a variable inside a function, that variable is considered local.[1] Thus, the line counter += 1 implicitly makes counter local to increment(). Trying to execute this … Read more
you may force the capture of a variable using an argument with a default value: >>> for i in [0,1,2,3]: … adders[i]=lambda a,i=i: i+a # note the dummy parameter with a default value … >>> print( adders[1](3) ) 4 the idea is to declare a parameter (cleverly named i) and give it a default value … Read more
Yes – take a copy of the variable inside the loop: while (variable < 5) { int copy = variable; actions.Add(() => copy * 2); ++ variable; } You can think of it as if the C# compiler creates a “new” local variable every time it hits the variable declaration. In fact it’ll create appropriate … Read more
Quoting myself for an explanation of the first example: JavaScript’s scopes are function-level, not block-level, and creating a closure just means that the enclosing scope gets added to the lexical environment of the enclosed function. After the loop terminates, the function-level variable i has the value 5, and that’s what the inner function ‘sees’. In … Read more
JavaScript closure inside loops – simple practical example
Sure, you can do: def italic(predecessor): x = predecessor def successor(): return “<italic/>” + x() + “</italic>” return successor Just like you can do: def italic(predecessor): x = predecessor x2 = x def successor(): return “<italic/>” + x2() + “</italic>” return successor or def italic(predecessor): x = predecessor x2 = x x3 = x2 def … Read more