The simple answer is that nil is not defined to be a valid value for type string in the language specification. …but maybe you want a longer answer? nil is the zero value for pointers, interfaces, channels, slices, maps and function types, and it represents an uninitialized state. Consider the following variable declarations: var a … Read more
One case when you need to include more structure on the left hand side of the assignment is when you’re asking Python unpack a slightly more complicated sequence. E.g.: # Works >>> a, (b, c) = [1, [2, 3]] # Does not work >>> a, b, c = [1, [2, 3]] Traceback (most recent call … Read more
In an assignment statement, the right-hand side is always evaluated fully before doing the actual setting of variables. So, x, y = y, x + y evaluates y (let’s call the result ham), evaluates x + y (call that spam), then sets x to ham and y to spam. I.e., it’s like ham = y … Read more
When Python parses the body of a function definition and encounters an assignment such as feed = … Python interprets feed as a local variable by default. If you do not wish for it to be a local variable, you must put global feed in the function definition. The global statement does not have to … Read more
What does dis tell us: Python 3.4.1 (default, May 19 2014, 13:10:29) [GCC 4.2.1 Compatible Apple LLVM 5.1 (clang-503.0.40)] on darwin Type “help”, “copyright”, “credits” or “license” for more information. >>> from dis import dis >>> dis(“””x = [1,2,3,4,5] … for x in x: … print(x) … print(x)”””) 1 0 LOAD_CONST 0 (1) 3 LOAD_CONST … Read more
Your understanding is wrong. self is itself a parameter to that function definition, so there’s no way it can be in scope at that point. It’s only in scope within the function itself. The answer is simply to default the argument to None, and then check for that inside the method: def doSomething(self, a=None): if … Read more
You use the function missing() for that. f <- function(p1, p2) { if(missing(p2)) { p2=p1^2 } p1-p2 } Alternatively, you can set the value of p2 to NULL by default. I sometimes prefer that solution, as it allows for passing arguments to nested functions. f <- function(p1, p2=NULL) { if(is.null(p2)) { p2=p1^2 } p1-p2 } … Read more
Not with object literals (this has the same value during constructing of the literal that it did before-hand). But you can do var carousel = new (function() { this.$slider = $(‘#carousel1 .slider’); this.panes = this.$slider.children().length; })(); This uses an object created from an anonymous function constructor. Note that $slider and panes are public, so can … Read more
Basically, the Logical AND operator (&&), will return the value of the second operand if the first is truthy, and it will return the value of the first operand if it is by itself falsy, for example: true && “foo”; // “foo” NaN && “anything”; // NaN 0 && “anything”; // 0 Note that falsy … Read more
In TF1, the statement x.assign(1) does not actually assign the value 1 to x, but rather creates a tf.Operation that you have to explicitly run to update the variable.* A call to Operation.run() or Session.run() can be used to run the operation: assign_op = x.assign(1) sess.run(assign_op) # or `assign_op.op.run()` print(x.eval()) # ==> 1 (* In … Read more