Tutorial by Examples: n

A table may be joined to itself, with different rows matching each other by some condition. In this use case, aliases must be used in order to distinguish the two occurrences of the table. In the below example, for each Employee in the example database Employees table, a record is returned containi...

The increment and decrement operators exist in prefix and postfix form. int a = 1; int b = 1; int tmp = 0; tmp = ++a; /* increments a by one, and returns new value; a == 2, tmp == 2 */ tmp = a++; /* increments a by one, but returns old value; a == 3, tmp == 2 */ tmp = --b; ...

The basic closure syntax is { [capture list] (parameters) throws-ness -> return type in body }. Many of these parts can be omitted, so there are several equivalent ways to write simple closures: let addOne = { [] (x: Int) -> Int in return x + 1 } let addOne = { [] (x: Int) -> Int in...

Functions may accept closures (or other functions) as parameters: func foo(value: Double, block: () -> Void) { ... } func foo(value: Double, block: Int -> Int) { ... } func foo(value: Double, block: (Int, Int) -> String) { ... } Trailing closure syntax If a function's last parameter ...

class MyClass { func sayHi() { print("Hello") } deinit { print("Goodbye") } } When a closure captures a reference type (a class instance), it holds a strong reference by default: let closure: () -> Void do { let obj = MyClass() // Captures a strong re...

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...

You can define a new class using the class keyword. class MyClass end Once defined, you can create a new instance using the .new method somevar = MyClass.new # => #<MyClass:0x007fe2b8aa4a18>

A class can have only one constructor, that is a method called initialize. The method is automatically invoked when a new instance of the class is created. class Customer def initialize(name) @name = name.capitalize end end sarah = Customer.new('sarah') sarah.name #=> 'Sarah' ...

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 ...

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...

In Python 2.6 and higher, math.copysign(x, y) returns x with the sign of y. The returned value is always a float. Python 2.x2.6 math.copysign(-2, 3) # 2.0 math.copysign(3, -3) # -3.0 math.copysign(4, 14.2) # 4.0 math.copysign(1, -0.0) # -1.0, on a platform which supports signed zero ...

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 2.x2.3 raw_input will wait for the user to enter text and then return the result as a string. foo = raw_input("Put a message here that asks the user for input") In the above example foo will store whatever input the user provides. Python 3.x3.0 input will wait for the user ...

Python 3.x3.0 In Python 3, print functionality is in the form of a function: print("This string will be displayed in the output") # This string will be displayed in the output print("You can print \n escape characters too.") # You can print escape characters too. Pyth...

def input_number(msg, err_msg=None): while True: try: return float(raw_input(msg)) except ValueError: if err_msg is not None: print(err_msg) def input_number(msg, err_msg=None): while True: try: return ...

Python 2.x2.3 In Python 2.x, to continue a line with print, end the print statement with a comma. It will automatically add a space. print "Hello,", print "World!" # Hello, World! Python 3.x3.0 In Python 3.x, the print function has an optional end parameter that is what...

The simplest way to iterate over a file line-by-line: with open('myfile.txt', 'r') as fp: for line in fp: print(line) readline() allows for more granular control over line-by-line iteration. The example below is equivalent to the one above: with open('myfile.txt', 'r') as fp: ...

The preferred method of file i/o is to use the with keyword. This will ensure the file handle is closed once the reading or writing has been completed. with open('myfile.txt') as in_file: content = in_file.read() print(content) or, to handle closing the file manually, you can forgo with...

with open('myfile.txt', 'w') as f: f.write("Line 1") f.write("Line 2") f.write("Line 3") f.write("Line 4") If you open myfile.txt, you will see that its contents are: Line 1Line 2Line 3Line 4 Python doesn't automatically add line b...

if (navigator.geolocation) { navigator.geolocation.getCurrentPosition(geolocationSuccess, geolocationFailure); } else { console.log("Geolocation is not supported by this browser."); } // Function that will be called if the query succeeds var geolocationSuccess = function(pos) {...