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The special symbol T represents the value true in Common Lisp, while the special symbol NIL represents false: CL-USER> (= 3 3) T CL-USER> (= 3 4) NIL They are called “Constant Variables” (sic!) in the standard, since they are variables whose value cannot be modified. As a consequence, y...

Actually any value different from NIL is considered a true value in Common Lisp. For instance: CL-USER> (let ((a (+ 2 2))) (if a a "Oh my! 2 + 2 is equal to NIL!")) 4 This fact can be combined with the boolean operators to make programs m...

R has a number of build in constants. The following constants are available: LETTERS: the 26 upper-case letters of the Roman alphabet letters: the 26 lower-case letters of the Roman alphabet month.abb: the three-letter abbreviations for the English month names month.name: the English names fo...

The command prompt comes pre-installed on all Windows NT, Windows CE, OS/2 and eComStation operating systems, and exists as cmd.exe, typically located in C:\Windows\system32\cmd.exe On Windows 7 the fastest ways to open the command prompt are: Press Win 𐌎, type "cmd" and then press ...

Any ASCII editor can edit batch files. A list of editors that can syntax highlight batch syntax can be found here. You can also use the default notepad shipped with windows to edit and view a batch file, although it does not offer syntax highlighting. To open notepad: Press Win 𐌎+R, type notepa...

To enable translation in templates you must load the i18n library. {% load i18n %} Basic translation is made with the trans template tag. {% trans "Some translatable text" %} {# equivalent to python `ugettext("Some translatable text")` #} The trans template tag supports ...

One could easily center a child element using table display property. HTML <div class="wrapper"> <div class="parent"> <div class="child"></div> </div> </div> CSS .wrapper { display: table; vertica...

Expires — specifies date when the resource becomes stale. It relies on servers and clients having accurate clocks and supporting time zones correctly. Cache-control: max-age takes precedence over Expires, and is generally more reliable. post-check and pre-check directives are non-standard I...

Many commands and programs in the remote side are screen-based (e.g. mc) or they need to ask password (e.g. sudo), to be able to run these kind of programs you can use option -t. ssh -t [email protected] sudo ls / [sudo] password for alice: bin root dev etc home lib mnt opt proc root run usr ...

Django handles a request by routing the incoming URL path to a view function. The view function is responsible for returning a response back to the client making the request. Different URLs are usually handled by different view functions. To route the request to a specific view function, Django look...

This is a very common workflow when using Ansible for provisioning an AWS EC2 instance. This post assumes a basic understand of Ansible and most importantly, assumes you've properly configured it to connect to AWS. As Ansible official documentation insists, we are going to use four roles: 1- ami_f...

Managing AWS resources that scale up and down runs into the limits of the static inventory host file, that's why we need something dynamic. And that's what the dynamic inventories are for. Let's start: Download these ec2.ini and ec2.py files to the your project folder: cd my_ansible_project wget...

If you are using multiple namespaces that may have same-name classes(such as System.Random and UnityEngine.Random), you can use an alias to specify that Random comes from one or the other without having to use the entire namespace in the call. For instance: using UnityEngine; using System; Ran...

Over time, our classes may implement more and more interfaces. When these interfaces have many methods, the total number of methods in our class will become very large. For example, let's suppose that we have two interfaces and a class implementing them: interface Printable { public functio...

To install an APK file, use the following command: adb install path/to/apk/file.apk or if the app is existing and we want to reinstall adb install -r path/to/apk/file.apk To uninstall an application, we have to specify its package adb uninstall application.package.name Use the following...

import cv2 image_path= #put your image path here #use imread() function to read image data to variable img. img = cv2.imread(image_path) #display image data in a new window with title 'I am an image display window' cv2.imshow('I am an image display window',img) #wait until user hi...

With the ~ selector, you can easily implement a global accessible boolean without using JavaScript. Add boolean as a checkbox To the very beginning of your document, add as much booleans as you want with a unique id and the hidden attribute set: <input type="checkbox" id="sideba...

Clojure functions can be defined with zero or more parameters. (defn welcome "Without parameters" [] "Hello!") (defn square "Take one parameter" [x] (* x x)) (defn multiplier "Two parameters" [x y] (* x y)) ...

First, Install gulp, gulp-clean-css and gulp-rename to project directory localy npm install --save-dev gulp gulp-clean-css gulp-rename Than add following minify-css task to your gulpfile.js var gulp = require('gulp'); var cleanCSS = require('gulp-clean-css'); var rename = require('gulp-rename...

An existing working copy can be quickly transformed to reflect the contents of a different branch in the same repository. For example, you might have a working copy of the trunk and now need to work on a development branch. Instead of checking out a completely new working copy (which can waste a l...