Tutorial by Examples: p

Say you have implemented some logic to detect attempts to modify an object in the database while the client that submitted changes didn't have the latest modifications. If such case happens, you raise a custom exception ConfictError(detailed_message). Now you want to return an HTTP 409 (Confict) st...

String to a primitive numeric type or a numeric wrapper type: Each numeric wrapper class provides a parseXxx method that converts a String to the corresponding primitive type. The following code converts a String to an int using the Integer.parseInt method: String string = "59"; int p...

The tile pane layout is similar to the FlowPane layout. TilePane places all of the nodes in a grid in which each cell, or tile, is the same size. It arranges nodes in neat rows and columns, either horizontally or vertically. import javafx.application.Application; import javafx.scene.Scene;...

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CSS ul { list-style: none; counter-reset: list-item-number; /* self nesting counter as name is same for all levels */ } li { counter-increment: list-item-number; } li:before { content: counters(list-item-number, ".") " "; /* usage of counters() function means val...

In many other languages, if you run the following (Java example) if("asgdsrf" == 0) { //do stuff } ... you'll get an error. You can't just go comparing strings to integers like that. In Python, this is a perfectly legal statement - it'll just resolve to False. A common gotcha ...

In the example of a message bubble illustrated below: the corners of the image should remain unchanged which is specified by UIEdgeInsets, but the borders and center of the image should expand to cover the new size. let insets = UIEdgeInsetsMake(12.0, 20.0, 22.0, 12.0) let image = UIImage(na...

Build constraints are commonly used to separate normal unit tests from integration tests that require external resources, like a database or network access. To do this, add a custom build constraint to the top of the test file: // +build integration package main import ( "testing&...

We can optimize a simple xor function for only architectures that support unaligned reads/writes by creating two files that define the function and prefixing them with a build constraint (for an actual example of the xor code which is out of scope here, see crypto/cipher/xor.go in the standard libra...

This is a simple but robust core-data set-up for iOS 10+. There are exactly two way to access core-data: viewContext. The viewContext can only be used from the main thread, and only for reading. strong enqueueCoreDataBlock. All writing should be done using enqueueCoreDataBlock. There is no ne...

// Core Data stack lazy var applicationDocumentsDirectory: NSURL = { let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask) return urls[urls.count-1] }() lazy var managedObjectModel: NSManagedObjectModel = { let modelURL = NSB...

lazy var persistentContainer: NSPersistentContainer = { let container = NSPersistentContainer(name: "ProjectName") container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error { fatalError("Unreso...

go() method The go() method loads a specific URL from the history list. The parameter can either be a number which goes to the URL within the specific position (-1 goes back one page, 1 goes forward one page), or a string. The string must be a partial or full URL, and the function will go to the f...

For Python, Guido van Rossum based the grouping of statements on indentation. The reasons for this are explained in the first section of the "Design and History Python FAQ". Colons, :, are used to declare an indented code block, such as the following example: class ExampleClass: #Eve...

The following example shows a basic main GUI window with a label widget, a toolbar, and a status bar using PyQt4. import sys from PyQt4 import QtGui class App(QtGui.QApplication): def __init__(self, sys_argv): super(App, self).__init__(sys_argv) self.build_ui() ...

The PBKDF2 algorithm exposed by hashlib module can be used to perform secure password hashing. While this algorithm cannot prevent brute-force attacks in order to recover the original password from the stored hash, it makes such attacks very expensive. import hashlib import os salt = os.urandom...

Let's add a custom operator to multiply a CGSize func *(lhs: CGFloat, rhs: CGSize) -> CGSize{ let height = lhs*rhs.height let width = lhs*rhs.width return CGSize(width: width, height: height) } Now this works let sizeA = CGSize(height:100, width:200) let sizeB = 1.1 * si...

When we have two separate array and we want to make key value pair from that two array, we can use array's reduce function like below: var columns = ["Date", "Number", "Size", "Location", "Age"]; var rows = ["2001", "5", "B...

char buf[8]; /* tiny buffer, easy to overflow */ printf("What is your name?\n"); scanf("%s", buf); /* WRONG */ scanf("%7s", buf); /* RIGHT */ If the user enters a string longer than 7 characters (- 1 for the null terminator), memory behind the buffer buf will be...

If realloc fails, it returns NULL. If you assign the value of the original buffer to realloc's return value, and if it returns NULL, then the original buffer (the old pointer) is lost, resulting in a memory leak. The solution is to copy into a temporary pointer, and if that temporary is not NULL, th...