syntactic-sugar

问题 In C/C++, switch/case compares only an integral type with a compile time constants. It's not possible to use them to compare user/library defined types like std::string with runtime values. Why the switch statement cannot be applied on strings? Can we implement look-a-like switch/case which gives similar syntactic sugar and serves the purpose of avoiding plain if/else comparisons. struct X { std::string s; bool operator== (const X& other) const { return s == other.s; } bool operator== (const

问题 This is what I'm doing now library(Rcpp) A <- diag(c(1.0, 2.0, 3.0)) rownames(A) <- c('X', 'Y', 'Z') colnames(A) <- c('A', 'B', 'C') cppFunction(' void scaleMatrix(NumericMatrix& A, double x) { A = A * x; }') Unfortunately It doesn't work :( > A A B C X 1 0 0 Y 0 2 0 Z 0 0 3 > scaleMatrix(A, 2) > A A B C X 1 0 0 Y 0 2 0 Z 0 0 3 I learned from Rcpp FAQ, Question 5.1 that Rcpp should be able to change the object I passed by value. Stealing an example from Dirk's answer to my previous question:

问题 This is what I'm doing now library(Rcpp) A <- diag(c(1.0, 2.0, 3.0)) rownames(A) <- c('X', 'Y', 'Z') colnames(A) <- c('A', 'B', 'C') cppFunction(' void scaleMatrix(NumericMatrix& A, double x) { A = A * x; }') Unfortunately It doesn't work :( > A A B C X 1 0 0 Y 0 2 0 Z 0 0 3 > scaleMatrix(A, 2) > A A B C X 1 0 0 Y 0 2 0 Z 0 0 3 I learned from Rcpp FAQ, Question 5.1 that Rcpp should be able to change the object I passed by value. Stealing an example from Dirk's answer to my previous question:

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Understanding Python decorators I am quite new on using Python decorators and from what I understand on my first impression that they are just syntactic sugar. Is there a more profound use of them for more complex uses ? 回答1: Yes it is syntactic sugar. Everything can be achieved without them, but with a few more lines of code. But it helps you write more concise code. Examples: from functools import wraps def

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Understanding Python decorators I am quite new on using Python decorators and from what I understand on my first impression that they are just syntactic sugar. Is there a more profound use of them for more complex uses ? 回答1: Yes it is syntactic sugar. Everything can be achieved without them, but with a few more lines of code. But it helps you write more concise code. Examples: from functools import wraps def

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Understanding Python decorators I am quite new on using Python decorators and from what I understand on my first impression that they are just syntactic sugar. Is there a more profound use of them for more complex uses ? 回答1: Yes it is syntactic sugar. Everything can be achieved without them, but with a few more lines of code. But it helps you write more concise code. Examples: from functools import wraps def

问题 def strange_syntax(stuff): return ".".join(item for item in stuff) How (and why) works this code? What happens here? Normally I can't use this syntax. Also, this syntax doesn't exist if it's not inside some function as an argument. I know, I could do the same with: def normal_syntax(stuff): return ".".join(stuff) 回答1: When used in a function call, the syntax: f(a for a in b) implicitly is compiled as a generator, meaning f((a for a in b)) This is just syntactic sugar, to make the program look

问题 The following AWK format: /REGEX/ {Action} Will execute Action if the current line matches REGEX . Is there a way to add an else clause, which will be executed if the current line does not matches the regex, without using if-then-else explicitly, something like: /REGEX/ {Action-if-matches} {Action-if-does-not-match} 回答1: Not so short: /REGEX/ {Action-if-matches} ! /REGEX/ {Action-if-does-not-match} But (g)awk supports the ternary operator too: { /REGEX/ ? matching=1 : matching = 0 ; if (

问题 The following AWK format: /REGEX/ {Action} Will execute Action if the current line matches REGEX . Is there a way to add an else clause, which will be executed if the current line does not matches the regex, without using if-then-else explicitly, something like: /REGEX/ {Action-if-matches} {Action-if-does-not-match} 回答1: Not so short: /REGEX/ {Action-if-matches} ! /REGEX/ {Action-if-does-not-match} But (g)awk supports the ternary operator too: { /REGEX/ ? matching=1 : matching = 0 ; if (

问题 Lists or numpy arrays can be unpacked to multiple variables if the dimensions match. For a 3xN array, the following will work: import numpy as np a,b = [[1,2,3],[4,5,6]] a,b = np.array([[1,2,3],[4,5,6]]) # result: a=[1,2,3], b=[4,5,6] How can I achieve a similar behaviour for the columns of a pandas DataFrame ? Extending the above example: import pandas as pd df = pd.DataFrame([[1,2,3],[4,5,6]]) df.columns = ['A','B','C'] # Rename cols and df.index = ['i', 'ii'] # rows for clarity The