expression

问题 I know that assignment is a statement in Python, i.e., it doesn't evaluate to a value unlike an expression. How does the following line of code work in Python, then? Please explain what happens internally in the Python interpreter (lexing, parsing, formation of abstract syntax tree). # this works spam = eggs = 'ham' # this doesn't work. Throws SyntaxError spam = (eggs = 'ham') 回答1: why the first line above works while the second doesn't? It's not about operator precedence. It's a designated

问题 In Chrome and Firefox, typeof foo evalulates to 'undefined' . But typeof (function() { return foo; })() throws an error: ReferenceError: foo is not defined This destroys the notions that I have of susbstitutability of expressions! Until now, I knew of no conditions for which foo and (function() { return foo; })() are not the same. Is this standard behavior? If so, it would be helpful to quote the relevant part of the ECMAScript standard. EDIT: Another example: typeof (foo) typeof (foo + 0) I

问题 This is an extension to a related question answered Here I have a weekly csv file which needs to be parsed. it looks like this. "asdf","asdf","asdf","asdf" But sometimes there are text fields which contain an extra unescaped double quote string like this "asdf","as "something" df","asdf","asdf" From the other posts on here, I was able to put together a regex (?m)""(?![ \t]*(,|$)) which matches two successive double quotes, only "if they DON'T have a comma or end-of-the-line ahead of them with

问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 6 years ago . Here is a list of examples of PHP regular expressions examples. Maybe this helps someone, as admin/ or another user can't make clear that I was trying to

问题 I am trying to label a plot with the following label: "Some Assay EC50 (uM)" where the "u" is a micro symbol. I currently have: assay <- "Some Assay" plot(0,xlab=expression(paste(assay," AC50 (",mu,"M)",sep=""))) But that gives: "assay EC50 (uM)" rather than the desired "Some Assay EC50 (uM)". Suggestions? Thanks. I also tried: paste(assay,expression(paste(" AC50 (",mu,"M)",sep="")),sep="") 回答1: You want a combination of bquote() and a bit of plotmath fu: assay <- "Some Assay" xlab <- bquote(

问题 I am quite new to programming. This is in relation to python. So the idea is to take an expression such as 3/5 or, at most, 3/5*2(at most two operators, note that the operators can be any of +,-,/,*) and solve it. White space can exist anywhere within the expression. The user enters the expression, say 3/5, and the program needs to solve the expression and display the answers. What I have tried is below. Note, I only have attempted the first part, once I can properly split the original

问题 How do I parse and evaluate expressions in an infix calculator grammar? I thought of two ways. The 1st involves using two stacks. One is for numbers and the other is for operators, and I would assess the operator precedence and association in order to figure out how to evaluate an expression. The second method involves converting the infix expression to postfix which I have no idea how I'd go about doing. It was just an idea. Currently I set up my program with the intention to use the 1st

问题 I need a way to recreate dynamically generated reports at some point in the future. Long story short, I need to store a specific linq query (different for each report) into database and then execute the query with dynamic Linq later on. This is all good, but I can't find a way to convert expression to string. As in: Expression<Func<Product, bool>> exp = (x) => (x.Id > 5 && x.Warranty != false); should become: "Product.Id > 5 && Product.Warranty != false" Is there a way to do that? 回答1: This

问题 I'm having performance problems with using reflection. So I decided to create delegates for the properties of my objects and so far got this: TestClass cwp = new TestClass(); var propertyInt = typeof(TestClass).GetProperties().Single(obj => obj.Name == "AnyValue"); var access = BuildGetAccessor(propertyInt.GetGetMethod()); var result = access(cwp); static Func<object, object> BuildGetAccessor(MethodInfo method) { var obj = Expression.Parameter(typeof(object), "o"); Expression<Func<object,

问题 This question already has answers here : How set value a property selector Expression<Func<T,TResult>> (6 answers) Closed 6 years ago . Given the following method: public static void SetPropertyValue(object target, string propName, object value) { var propInfo = target.GetType().GetProperty(propName, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.DeclaredOnly); if (propInfo == null) throw new ArgumentOutOfRangeException("propName", "Property not found on