Tutorial by Examples: d

List and Details views

Template views are fine for static page and you could use them for everything with get_context_data but it would be barely better than using function as views. Enter ListView and DetailView app/models.py from django.db import models class Pokemon(models.Model): name = models.CharField(max...

Django • Class based views

Form and object creation

Writing a view to create object can be quite boring. You have to display a form, you have to validate it, you have to save the item or return the form with an error. Unless you use one of the generic editing views. app/views.py from django.core.urlresolvers import reverse_lazy from django.views.g...

Django • Class based views

Creating a random user password

In order to create a random user password we can use the symbols provided in the string module. Specifically punctuation for punctuation symbols, ascii_letters for letters and digits for digits: from string import punctuation, ascii_letters, digits We can then combine all these symbols in a name...

Python Language • Random module

Starting a new thread

To start a new thread: use std::thread; fn main() { thread::spawn(move || { // The main thread will not wait for this thread to finish. That // might mean that the next println isn't even executed before the // program exits. println!("Hello from spa...

Rust • Parallelism

Setting Minimum and Maximum dates for a datepicker

jQuery UI Library • Datepicker

Why use Default Methods?

The simple answer is that it allows you to evolve an existing interface without breaking existing implementations. For example, you have Swim interface that you published 20 years ago. public interface Swim { void backStroke(); } We did a great job, our interface is very popular, there ar...

Java Language • Default Methods

Speeding tough-to-vectorize for loops by byte compiling

Following the Rcpp example in this documentation entry, consider the following tough-to-vectorize function, which creates a vector of length len where the first element is specified (first) and each element x_i is equal to cos(x_{i-1} + 1): repeatedCosPlusOne <- function(first, len) { x <-...

R Language • Speeding up tough-to-vectorize code

Creating a model with relationships

Many-to-One Relationship from django.db import models class Author(models.Model): name = models.CharField(max_length=50) #Book has a foreignkey (many to one) relationship with author class Book(models.Model): author = models.ForeignKey(Author, on_delete=models.CASCADE) publish_...

Django • Models

Basic Django DB queries

Django ORM is a powerful abstraction that lets you store and retrieve data from the database without writing sql queries yourself. Let's assume the following models: class Author(models.Model): name = models.CharField(max_length=50) class Book(models.Model): name = models.CharField(max...

Django • Models

jQuery UI Sortable - Drop Placeholder

This example of the Sortable using a Placeholder is common usage. Sortable is applied to a group of DOM elements, allowing the user to move items around in the list via Drag'n Drop style actions. <!doctype html> <html lang="en"> <head> <meta charset="utf-8&q...

jQuery UI Library • jquery ui sortable

Using modules from other program units

To access entities declared in a module from another program unit (module, procedure or program), the module must be used with the use statement. module shared_data implicit none integer :: iarray(4) = [1, 2, 3, 4] real :: rarray(4) = [1., 2., 3., 4.] end module program test !...

Fortran • Usage of Modules

A basic unmanaged table.

At some point in your use of Django, you may find yourself wanting to interact with tables which have already been created, or with database views. In these cases, you would not want Django to manage the tables through its migrations. To set this up, you need to add only one variable to your model's...

Django • Models

Background Position

The background-position property is used to specify the starting position for a background image or gradient .myClass { background-image: url('path/to/image.jpg'); background-position: 50% 50%; } The position is set using an X and Y co-ordinate and be set using any of the units used withi...

CSS • Backgrounds

Simple text input widget

The most simple example of widget is custom text input. For instance, to create an <input type="tel">, you have to subclass TextInput and set input_type to 'tel'. from django.forms.widgets import TextInput class PhoneInput(TextInput): input_type = 'tel'

Django • Form Widgets

Composite widget

You can create widgets composed of multiple widgets using MultiWidget. from datetime import date from django.forms.widgets import MultiWidget, Select from django.utils.dates import MONTHS class SelectMonthDateWidget(MultiWidget): """This widget allows the user to fill in ...

Django • Form Widgets

Using custom deleters to create a wrapper to a C interface

Many C interfaces such as SDL2 have their own deletion functions. This means that you cannot use smart pointers directly: std::unique_ptr<SDL_Surface> a; // won't work, UNSAFE! Instead, you need to define your own deleter. The examples here use the SDL_Surface structure which should be fre...

C++ • Smart Pointers

Lens and Prism

A Lens' s a means that you can always find an a within any s. A Prism' s a means that you can sometimes find that s actually just is a but sometimes it's something else. To be more clear, we have _1 :: Lens' (a, b) a because any tuple always has a first element. We have _Just :: Prism' (Maybe a) a...

Haskell Language • Lens

Table-driven unit tests

This type of testing is popular technique for testing with predefined input and output values. Create a file called main.go with content: package main import ( "fmt" ) func main() { fmt.Println(Sum(4, 5)) } func Sum(a, b int) int { return a + b } After you r...

Go • Testing

Example tests (self documenting tests)

This type of tests make sure that your code compiles properly and will appear in the generated documentation for your project. In addition to that, the example tests can assert that your test produces proper output. sum.go: package sum // Sum calculates the sum of two integers func Sum(a, b in...

Go • Testing

Simple queries on a standalone model

Here is a simple model that we will use to run a few test queries: class MyModel(models.Model): name = models.CharField(max_length=10) model_num = models.IntegerField() flag = models.NullBooleanField(default=False) Get a single model object where the id/pk is 4: (If there are no...

Django • Querysets