Tutorial by Examples: le

Assuming python and python3 are both installed, it is possible to create a virtual environment for Python 3 even if python3 is not the default Python: virtualenv -p python3 foo or virtualenv --python=python3 foo or python3 -m venv foo or pyvenv foo Actually you can create virtual ...

Getting ("a", 1) ^. _1 -- returns "a" ("a", 1) ^. _2 -- returns 1 Setting ("a", 1) & _1 .~ "b" -- returns ("b", 1) Modifying ("a", 1) & _2 %~ (+1) -- returns ("a", 2) both Traversal (1, 2) & bot...

Simple record {-# LANGUAGE TemplateHaskell #-} import Control.Lens data Point = Point { _x :: Float, _y :: Float } makeLenses ''Point Lenses x and y are created. let p = Point 5.0 6.0 p ^. x -- returns 5.0 set x 10 p -- returns Point { _x = 10.0, _y = 6.0 } p & x +~ ...

Requirements: Installed Java JDK or JRE (version 7 or higher for Gradle 3.x version) Installation steps: Download Gradle distribution from the official web site Unpack the ZIP Add the GRADLE_HOME environment variable. This variable should point to the unpacked files from the previous step. Ad...

First of all, implement your view holder: implements View.OnClickListener, View.OnLongClickListener Then, register the listeners as follows: itemView.setOnClickListener(this); itemView.setOnLongClickListener(this); Next, override the listeners as follows: @Override public void onClick(Vie...

By default error message appears below textbox in <div class="help-block"></div> on keyUp or after pressing submit button if any validation constraints aren't met. Sometimes we want a message on submit only i.e. no validation at onKeyup event. Let's check yii2/widgets/ActiveF...

An interface in Kotlin can have default implementations for functions: interface MyInterface { fun withImplementation() { print("withImplementation() was called") } } Classes implementing such interfaces will be able to use those functions without reimplementing cl...

INSERT INTO `my_table` (`field_1`, `field_2`) VALUES ('data_1', 'data_2'), ('data_1', 'data_3'), ('data_4', 'data_5'); This is an easy way to add several rows at once with one INSERT statement. This kind of 'batch' insert is much faster than inserting rows one by one. Typically...

Pseudo-elements are added to selectors but instead of describing a special state, they allow you to style certain parts of a document. The content attribute is required for pseudo-elements to render; however, the attribute can have an empty value (e.g. content: ""). div::after { conte...

The double-negation !! is not a distinct JavaScript operator nor a special syntax but rather just a sequence of two negations. It is used to convert the value of any type to its appropriate true or false Boolean value depending on whether it is truthy or falsy. !!1 // true !!0 ...

While loops and do while loops are allowed in Dart: while(peopleAreClapping()) { playSongs(); } and: do { processRequest(); } while(stillRunning()); Loops can be terminated using a break: while (true) { if (shutDownRequested()) break; processIncomingRequests(); } You can s...

x = (1, 2, 3) x[0] # 1 x[1] # 2 x[2] # 3 x[3] # IndexError: tuple index out of range Indexing with negative numbers will start from the last element as -1: x[-1] # 3 x[-2] # 2 x[-3] # 1 x[-4] # IndexError: tuple index out of range Indexing a range of elements print(x[:-1]) # (1,...

SELECT * FROM Employees ORDER BY LName This statement will return all the columns from the table Employees. IdFNameLNamePhoneNumber2JohnJohnson24681012141JamesSmith12345678903MichaelWilliams1357911131 SELECT * FROM Employees ORDER BY LName DESC Or SELECT * FROM Employees ORDER BY LName ASC...

If a name is bound inside a function, it is by default accessible only within the function: def foo(): a = 5 print(a) # ok print(a) # NameError: name 'a' is not defined Control flow constructs have no impact on the scope (with the exception of except), but accessing variable that w...

x and y are extracted from the tuple: val (x, y) = (1337, 42) // x: Int = 1337 // y: Int = 42 To ignore a value use _: val (_, y: Int) = (1337, 42) // y: Int = 42 To unpack an extractor: val myTuple = (1337, 42) myTuple._1 // res0: Int = 1337 myTuple._2 // res1: Int = 42 Note that...

The null coalescing operator makes it easy to ensure that a method that may return null will fall back to a default value. Without the null coalescing operator: string name = GetName(); if (name == null) name = "Unknown!"; With the null coalescing operator: string name = GetN...

One of the main differences between lists and tuples in Python is that tuples are immutable, that is, one cannot add or modify items once the tuple is initialized. For example: >>> t = (1, 4, 9) >>> t[0] = 2 Traceback (most recent call last): File "<stdin>", l...

With promises: function doTheThing() { return doOneThing() .then(doAnother) .then(doSomeMore) .catch(handleErrors) } With async functions: async function doTheThing() { try { const one = await doOneThing(); const another = await doAnother(...

HTML <div class="scale"></div> CSS .scale { width: 100px; height: 100px; background: teal; transform: scale(0.5, 1.3); } This example will scale the div to 100px * 0.5 = 50px on the X axis and to 100px * 1.3 = 130px on the Y axis. The center of the...

You can handle multiple errors in the same rescue declaration: begin # an execution that may fail rescue FirstError, SecondError => e # do something if a FirstError or SecondError occurs end You can also add multiple rescue declarations: begin # an execution that may fail rescue ...