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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...

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...

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...

var x = true, y = false; AND This operator will return true if both of the expressions evaluate to true. This boolean operator will employ short-circuiting and will not evaluate y if x evaluates to false. x && y; This will return false, because y is false. OR This operator wil...

The exit construct can be used to pass a return code to the executing environment. #!/usr/bin/php if ($argv[1] === "bad") { exit(1); } else { exit(0); } By default an exit code of 0 will be returned if none is provided, i.e. exit is the same as exit(0). As exit is not a ...

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': ...

At the command line, first verify that you have Git installed: On all operating systems: git --version On UNIX-like operating systems: which git If nothing is returned, or the command is not recognized, you may have to install Git on your system by downloading and running the installer. See...

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....

Consider a database with the following two tables. Employees table: IdFNameLNameDeptId1JamesSmith32JohnJohnson4 Departments table: IdName1Sales2Marketing3Finance4IT Simple select statement * is the wildcard character used to select all available columns in a table. When used as a substitute f...

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...

Logical OR (||), reading left to right, will evaluate to the first truthy value. If no truthy value is found, the last value is returned. var a = 'hello' || ''; // a = 'hello' var b = '' || []; // b = [] var c = '' || undefined; // c = undefined var d = 1 |...

Continuing a "for" Loop When you put the continue keyword in a for loop, execution jumps to the update expression (i++ in the example): for (var i = 0; i < 3; i++) { if (i === 1) { continue; } console.log(i); } Expected output: 0 2 Continuing a While...

Decorators augment the behavior of other functions or methods. Any function that takes a function as a parameter and returns an augmented function can be used as a decorator. # This simplest decorator does nothing to the function being decorated. Such # minimal decorators can occasionally be used ...

As mentioned in the introduction, a decorator is a function that can be applied to another function to augment its behavior. The syntactic sugar is equivalent to the following: my_func = decorator(my_func). But what if the decorator was instead a class? The syntax would still work, except that now m...

Decorators normally strip function metadata as they aren't the same. This can cause problems when using meta-programming to dynamically access function metadata. Metadata also includes function's docstrings and its name. functools.wraps makes the decorated function look like the original function b...

A decorator takes just one argument: the function to be decorated. There is no way to pass other arguments. But additional arguments are often desired. The trick is then to make a function which takes arbitrary arguments and returns a decorator. Decorator functions def decoratorfactory(message): ...

When you define a function, it creates a scope. Everything defined within the function is not accessible by code outside the function. Only code within this scope can see the entities defined inside the scope. function foo() { var a = 'hello'; console.log(a); // => 'hello' } consol...

About Protocols A Protocol specifies initialisers, properties, functions, subscripts and associated types required of a Swift object type (class, struct or enum) conforming to the protocol. In some languages similar ideas for requirement specifications of subsequent objects are known as ‘interfaces...

break statement When a break statement executes inside a loop, control flow "breaks" out of the loop immediately: i = 0 while i < 7: print(i) if i == 4: print("Breaking from loop") break i += 1 The loop conditional will not be evaluated a...

var re = /[a-z]+/; if (re.test("foo")) { console.log("Match exists."); } The test method performs a search to see if a regular expression matches a string. The regular expression [a-z]+ will search for one or more lowercase letters. Since the pattern matches the string,...