Tutorial by Examples: e

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

Roots: nth-root with fractional exponents

While the math.sqrt function is provided for the specific case of square roots, it's often convenient to use the exponentiation operator (**) with fractional exponents to perform nth-root operations, like cube roots. The inverse of an exponentiation is exponentiation by the exponent's reciprocal. S...

Python Language • Exponentiation

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

Format literals (f-string)

Literal format strings were introduced in PEP 498 (Python3.6 and upwards), allowing you to prepend f to the beginning of a string literal to effectively apply .format to it with all variables in the current scope. >>> foo = 'bar' >>> f'Foo is {foo}' 'Foo is bar' This works wi...

Python Language • String Formatting

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

Logging to Syslog service

It is possible to configure Django to output log to a local or remote syslog service. This configuration uses the python builtin SysLogHandler. from logging.handlers import SysLogHandler LOGGING = { 'version': 1, 'disable_existing_loggers': True, 'formatters': { 'standard':...

Django • Logging

Testing - a complete example

This assumes that you have read the documentation about starting a new Django project. Let us assume that the main app in your project is named td (short for test driven). To create your first test, create a file named test_view.py and copy paste the following content into it. from django.test impo...

Django • Unit Testing

Installation or Setup

Detailed instructions on getting couchbase set up or installed.

couchbase • Getting started with couchbase

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

Writing a lens without Template Haskell

To demystify Template Haskell, suppose you have data Example a = Example { _foo :: Int, _bar :: a } then makeLenses 'Example produces (more or less) foo :: Lens' (Example a) Int bar :: Lens (Example a) (Example b) a b There's nothing particularly magical going on, though. You can write ...

Haskell Language • Lens

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

Traversals

A Traversal' s a shows that s has 0-to-many as inside of it. toListOf :: Traversal' s a -> (s -> [a]) Any type t which is Traversable automatically has that traverse :: Traversal (t a) a. We can use a Traversal to set or map over all of these a values > set traverse 1 [1..10] [1,1,1,...

Haskell Language • Lens

Lenses compose

If you have a f :: Lens' a b and a g :: Lens' b c then f . g is a Lens' a c gotten by following f first and then g. Notably: Lenses compose as functions (really they just are functions) If you think of the view functionality of Lens, it seems like data flows "left to right"—this might ...

Haskell Language • Lens

Basic Test

main.go: package main import ( "fmt" ) func main() { fmt.Println(Sum(4,5)) } func Sum(a, b int) int { return a + b } main_test.go: package main import ( "testing" ) // Test methods start with `Test` func TestSum(t *testing.T) { go...

Go • Testing

Benchmark tests

If you want to measure benchmarks add a testing method like this: sum.go: package sum // Sum calculates the sum of two integers func Sum(a, b int) int { return a + b } sum_test.go: package sum import "testing" func BenchmarkSum(b *testing.B) { for i := 0; i < ...

Go • Testing