Tutorial by Examples: ar

Global Variables

In Python, variables inside functions are considered local if and only if they appear in the left side of an assignment statement, or some other binding occurrence; otherwise such a binding is looked up in enclosing functions, up to the global scope. This is true even if the assignment statement is ...

Python Language • Variable Scope and Binding

Changing the sequence you are iterating over

A for loop iterates over a sequence, so altering this sequence inside the loop could lead to unexpected results (especially when adding or removing elements): alist = [0, 1, 2] for index, value in enumerate(alist): alist.pop(index) print(alist) # Out: [1] Note: list.pop() is being used t...

Python Language • Common Pitfalls

Class and instance variables

There are several special variable types that a class can use for more easily sharing data. Instance variables, preceded by @. They are useful if you want to use the same variable in different methods. class Person def initialize(name, age) my_age = age # local variable, will be destroyed ...

Ruby Language • Classes

Accessing instance variables with getters and setters

We have three methods: attr_reader: used to allow reading the variable outside the class. attr_writer: used to allow modifying the variable outside the class. attr_accessor: combines both methods. class Cat attr_reader :age # you can read the age but you can never change it attr_writer...

Ruby Language • Classes

Logarithms

math.log(x) gives the natural (base e) logarithm of x. math.log(math.e) # 1.0 math.log(1) # 0.0 math.log(100) # 4.605170185988092 math.log can lose precision with numbers close to 1, due to the limitations of floating-point numbers. In order to accurately calculate logs close to 1, ...

Python Language • Math Module

Defining a function with optional mutable arguments

There is a problem when using optional arguments with a mutable default type (described in Defining a function with optional arguments), which can potentially lead to unexpected behaviour. Explanation This problem arises because a function's default arguments are initialised once, at the point whe...

Python Language • Functions

Basics of Arrays

Array is an ordered collection type in the Swift standard library. It provides O(1) random access and dynamic reallocation. Array is a generic type, so the type of values it contains are known at compile time. As Array is a value type, its mutability is defined by whether it is annotated as a var (...

Swift Language • Arrays

Accessing Array Values

The following examples will use this array to demonstrate accessing values var exampleArray:[Int] = [1,2,3,4,5] //exampleArray = [1, 2, 3, 4, 5] To access a value at a known index use the following syntax: let exampleOne = exampleArray[2] //exampleOne = 3 Note: The value at index two is th...

Swift Language • Arrays

Modifying values in an array

There are multiple ways to append values onto an array var exampleArray = [1,2,3,4,5] exampleArray.append(6) //exampleArray = [1, 2, 3, 4, 5, 6] var sixOnwards = [7,8,9,10] exampleArray += sixOnwards //exampleArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] and remove values from an array exampleAr...

Swift Language • Arrays

Making a shallow copy of an array

A quick way to make a copy of an array (as opposed to assigning a variable with another reference to the original array) is: arr[:] Let's examine the syntax. [:] means that start, end, and slice are all omitted. They default to 0, len(arr), and 1, respectively, meaning that subarray that we are ...

Python Language • Indexing and Slicing

Get Started

Download Xcode from the Mac App Store. Click to create a new project or playground:

Xcode • Getting started with Xcode

Getting Started

Create a new HTML file and paste the following content: <!DOCTYPE html> <html ng-app> <head> <title>Hello, Angular</title> <script src="https://code.angularjs.org/1.5.8/angular.min.js"></script> </head> <body ng-init="name=...

AngularJS • Getting started with AngularJS

Hello World Using Variables

Create a new file called hello.sh with the following content and give it executable permissions with chmod +x hello.sh. Execute/Run via: ./hello.sh #!/usr/bin/env bash # Note that spaces cannot be used around the `=` assignment operator whom_variable="World" # Use printf to sa...

Bash • Getting started with Bash

Getting Started

Creating a database in MySQL CREATE DATABASE mydb; Return value: Query OK, 1 row affected (0.05 sec) Using the created database mydb USE mydb; Return value: Database Changed Creating a table in MySQL CREATE TABLE mytable ( id int unsigned NOT NULL auto_increme...

MySQL • Getting started with MySQL

Logarithms

By default, the math.log function calculates the logarithm of a number, base e. You can optionally specify a base as the second argument. import math import cmath math.log(5) # = 1.6094379124341003 # optional base argument. Default is math.e math.log(5, math.e) # = 1.6094379124341003 ...

Python Language • Simple Mathematical Operators

Apply Margin on a Given Side

Direction-Specific Properties CSS allows you to specify a given side to apply margin to. The four properties provided for this purpose are: margin-left margin-right margin-top margin-bottom The following code would apply a margin of 30 pixels to the left side of the selected div. View Resu...

CSS • Margins

Counting number of times a substring appears in a string

One method is available for counting the number of occurrences of a sub-string in another string, str.count. str.count(sub[, start[, end]]) str.count returns an int indicating the number of non-overlapping occurrences of the sub-string sub in another string. The optional arguments start and end ...

Python Language • String Methods

Declaring Dictionaries

Dictionaries are an unordered collection of keys and values. Values relate to unique keys and must be of the same type. When initializing a Dictionary the full syntax is as follows: var books : Dictionary<Int, String> = Dictionary<Int, String>() Although a more concise way of initia...

Swift Language • Dictionaries

Modifying Dictionaries

Add a key and value to a Dictionary var books = [Int: String]() //books = [:] books[5] = "Book 5" //books = [5: "Book 5"] books.updateValue("Book 6", forKey: 5) //[5: "Book 6"] updateValue returns the original value if one exists or nil. let previous...

Swift Language • Dictionaries

Article Element

The <article> element contains self-contained content like articles, blog posts, user comments or an interactive widget that could be distributed outside the context of the page, for example by RSS. When article elements are nested, the contents of the inner article node should be related t...

HTML • Sectioning Elements