scoping

I've been going through Javascript function scope and have run into this: var scope = "global"; function f(){ console.log(scope); var scope = "local"; console.log(scope); } f(); Now I understand that the output of the first log is "undefined" because of how js hoists variables at the top of the function. BUT when I remove var from "var scope = "local";" the first log outputs "global" and this has got me scratching my head. Can someone explain why that is happening please? I mean doesn't js sequentially run the code? As such how can removing VAR have any impact on the first log? Two-pass

This question already has an answer here: Scoping in Python 'for' loops 6 answers Consider this example: for iter in xrange(10): myvar = iter print myvar # 9 Here myvar is clearly outside the loop? But it is still accessible. If this is Perl, it will throw an error. What's the reason behind such feature in Python? Is it harmful? What's the best practice then, to declare a variable before looping? There is no new scope created by the for loop (Ruby also behaves the same way). This may be surprising if you are coming from a language that creates new scopes for blocks. I don't believe it's

>>> x = 'foo' >>> {0: locals().get('x')} {0: 'foo'} >>> {0: locals().get('x' + spam) for spam in ['']} {0: None} What is the reason for this discrepancy in behaviour? Dict comprehensions and generator comprehensions create their own local scope. List comprehensions do not in Python 2.x, but do in Python 3. (Note that your first example is not a dict comprehension. It's just a literal dict that happens to have an expression as the value for the key 0.) 来源： https://stackoverflow.com/questions/13117020/python-scoping-in-dict-comprehension

I have a Javascript "class" defined like so: var Welcomer = function(name) { var pName = name; var pMessage = function() { return "Hi, " + pName + "!"; }; return { sayHi: function() { alert(pMessage()); } }; }; new Welcomer('Sue').sayHi(); Is there a way to "subclass" Welcomer in such a way that I can redefine the public methods and have access to the private methods and variables? The following will give me access to the public methods, but not to the private ones: var UnhappyWelcomer = function(name) { var pSadMessage = function() { // won't work, b/c I don't have access to pMessage return

This question already has an answer here: How to check if object (variable) is defined in R? 6 answers I want to determine whether an object exists inside a function in R: foo <- function() { y <- "hello" if (exists(y, envir = sys.frame())) print(y) } foo() Error in exists(y, envir = sys.frame()) : invalid first argument I thought adding the envir = sys.frame() would do the trick. Also tried envir = environment() Expected foo() "hello" You should have checked ?exists : Usage: exists(x, where = -1, envir = , frame, mode = "any", inherits = TRUE) Arguments: x: a variable name (given as a

Let me add another scoping problem in R, this time with the snowfall package. If I define a function in my global environment, and I try to use that one later in an sfApply() inside another function, my first function isn't found any more : #Runnable code. Don't forget to stop the cluster with sfStop() require(snowfall) sfInit(parallel=TRUE,cpus=3) func1 <- function(x){ y <- x+1 y } func2 <- function(x){ y <- sfApply(x,2,function(i) func1(i) ) y } y <- matrix(1:10,ncol=2) func2(y) sfStop() This gives : > func2(y) Error in checkForRemoteErrors(val) : 2 nodes produced errors; first error: could