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The fundamental part of most classes is its constructor, which sets up each instance's initial state and handles any parameters that were passed when calling new. It's defined in a class block as though you're defining a method named constructor, though it's actually handled as a special case. cla...

Set comprehension is similar to list and dictionary comprehension, but it produces a set, which is an unordered collection of unique elements. Python 2.x2.7 # A set containing every value in range(5): {x for x in range(5)} # Out: {0, 1, 2, 3, 4} # A set of even numbers between 1 and 10: {x f...

In some cases, when working with a web server, overriding the web server's default content type may be required. There may be cases where you need to send data as plain text, JSON, or XML, for example. The header() function can send a raw HTTP header. You can add the Content-Type header to notify t...

The addition operator (+) adds numbers. var a = 9, b = 3, c = a + b; c will now be 12 This operand can also be used multiple times in a single assignment: var a = 9, b = 3, c = 8, d = a + b + c; d will now be 20. Both operands are converted to primitive types. ...

The subtraction operator (-) subtracts numbers. var a = 9; var b = 3; var c = a - b; c will now be 6 If a string or boolean is provided in place of a number value, it gets converted to a number before the difference is calculated (0 for false, 1 for true): "5" - 1; // 4 7 - ...

The multiplication operator (*) perform arithmetic multiplication on numbers (literals or variables). console.log( 3 * 5); // 15 console.log(-3 * 5); // -15 console.log( 3 * -5); // -15 console.log(-3 * -5); // 15

The division operator (/) perform arithmetic division on numbers (literals or variables). console.log(15 / 3); // 5 console.log(15 / 4); // 3.75

Exponentiation makes the second operand the power of the first operand (ab). var a = 2, b = 3, c = Math.pow(a, b); c will now be 8 6 Stage 3 ES2016 (ECMAScript 7) Proposal: let a = 2, b = 3, c = a ** b; c will now be 8 Use Math.pow to find the nth root of a number....

ConstantsDescriptionApproximateMath.EBase of natural logarithm e2.718Math.LN10Natural logarithm of 102.302Math.LN2Natural logarithm of 20.693Math.LOG10EBase 10 logarithm of e0.434Math.LOG2EBase 2 logarithm of e1.442Math.PIPi: the ratio of circle circumference to diameter (π)3.14Math.SQRT1_2Square ro...

All angles below are in radians. An angle r in radians has measure 180 * r / Math.PI in degrees. Sine Math.sin(r); This will return the sine of r, a value between -1 and 1. Math.asin(r); This will return the arcsine (the reverse of the sine) of r. Math.asinh(r) This will return the hype...

Given a list comprehension you can append one or more if conditions to filter values. [<expression> for <element> in <iterable> if <condition>] For each <element> in <iterable>; if <condition> evaluates to True, add <expression> (usually a function...

dictionary = {"Hello": 1234, "World": 5678} print(dictionary["Hello"]) The above code will print 1234. The string "Hello" in this example is called a key. It is used to lookup a value in the dict by placing the key in square brackets. The number 1234 is ...

The dict() constructor can be used to create dictionaries from keyword arguments, or from a single iterable of key-value pairs, or from a single dictionary and keyword arguments. dict(a=1, b=2, c=3) # {'a': 1, 'b': 2, 'c': 3} dict([('d', 4), ('e', 5), ('f', 6)]) # {'d': 4, 'e': ...

When both operands are numeric, they are compared normally: 1 < 2 // true 2 <= 2 // true 3 >= 5 // false true < false // false (implicitly converted to numbers, 1 > 0) When both operands are strings, they are compared lexicographically (according to alphabeti...

Program options can be handled with the getopt() function. It operates with a similar syntax to the POSIX getopt command, with additional support for GNU-style long options. #!/usr/bin/php // a single colon indicates the option takes a value // a double colon indicates the value may be omitted ...

The git clone command is used to copy an existing Git repository from a server to the local machine. For example, to clone a GitHub project: cd <path where you'd like the clone to create a directory> git clone https://github.com/username/projectname.git To clone a BitBucket project: cd ...

In its most simple form, an if condition can be used like this: var i = 0; if (i < 1) { console.log("i is smaller than 1"); } The condition i < 1 is evaluated, and if it evaluates to true the block that follows is executed. If it evaluates to false, the block is skipped....

The JSONSerialization class is built into Apple's Foundation framework. 2.2 Read JSON The JSONObjectWithData function takes NSData, and returns AnyObject. You can use as? to convert the result to your expected type. do { guard let jsonData = "[\"Hello\", \"JSON\"]&q...

An enum provides a set of related values: enum Direction { case up case down case left case right } enum Direction { case up, down, left, right } Enum values can be used by their fully-qualified name, but you can omit the type name when it can be inferred: let dir = Dire...

This example assumes Ruby and Ruby on Rails have already been installed properly. If not, you can find how to do it here. Open up a command line or terminal. To generate a new rails application, use rails new command followed by the name of your application: $ rails new my_app If you want to c...