Tutorial by Examples: el

Effects of the del command

Removing a variable name from the scope using del v, or removing an object from a collection using del v[item] or del[i:j], or removing an attribute using del v.name, or any other way of removing references to an object, does not trigger any destructor calls or any memory being freed in and of itsel...

Python Language • Garbage Collection

Select by position

The iloc (short for integer location) method allows to select the rows of a dataframe based on their position index. This way one can slice dataframes just like one does with Python's list slicing. df = pd.DataFrame([[11, 22], [33, 44], [55, 66]], index=list("abc")) df # Out: # 0...

pandas • Indexing and selecting data

Implement Singleton pattern with a single-element enum

Enum constants are instantiated when an enum is referenced for the first time. Therefore, that allows to implement Singleton software design pattern with a single-element enum. public enum Attendant { INSTANCE; private Attendant() { // perform some initialization routine ...

Java Language • Enums

Using ActiveModel::Validations

You can validate any object, even plain ruby. class User include ActiveModel::Validations attr_reader :name, :age def initialize(name, age) @name = name @age = age end validates :name, presence: true validates :age, numericality: { only_integer: true, greater_than...

Ruby on Rails • ActiveModel

"Hello, World!" Program

To start using Vue.js, make sure you have the script file included in your HTML. For example, add the following to your HTML. <script src="https://npmcdn.com/vue/dist/vue.js"></script> Simple Example HTML template <div id="app"> {{ message }} </div&...

Vue.js • Getting started with Vue.js

Swift - UICollectionViewDelegateFlowLayout

// MARK: - UICollectionViewDelegateFlowLayout extension ViewController: UICollectionViewDelegateFlowLayout { func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize { return ...

iOS • UICollectionView

Indented code blocks inside lists

When adding indented code blocks inside a list you first need a blank line, then to indent the code further. Different flavours of Markdown have different rules for this. StackExchange requires code to be indented by 8 characters instead of the usual 4. (Spaces replaced with * for clarity): 1...

Markdown • Code

Currency Formatting US Dollars Using the locale Module

import locale locale.setlocale(locale.LC_ALL, '') Out[2]: 'English_United States.1252' locale.currency(762559748.49) Out[3]: '$762559748.49' locale.currency(762559748.49, grouping=True) Out[4]: '$762,559,748.49'

Python Language • The locale Module

Destructuring remaining elements into a sequence

Let's say you have a vector like so: (def my-vec [1 2 3 4 5 6]) And you want to extract the first 3 elements and get the remaining elements as a sequence. This can be done as follows: (let [[x y z & remaining] my-vec] (println "first:" x ", second:" y "third:&quot...

clojure • Clojure destructuring

#![no_std] Hello, World!

#![feature(start, libc, lang_items)] #![no_std] #![no_main] // The libc crate allows importing functions from C. extern crate libc; // A list of C functions that are being imported extern { pub fn printf(format: *const u8, ...) -> i32; } #[no_mangle] // The main function, with...

Rust • Bare Metal Rust

Alternative loop syntax

You can also use loop with curly brackets like this: if ( have_posts() ) { while ( have_posts() ) { the_post(); var_dump( $post ); } }

WordPress • The Loop (main WordPress loop)

Handling no items in the loop

If you want to handle such scenario just add an if/else statement. if ( have_posts() ) : while ( have_posts() ) : the_post(); var_dump( $post ); endwhile; else : __('This Query does not have any results'); endif;

WordPress • The Loop (main WordPress loop)

Calculate Content Bounds (for i.e. dynamic cell heights)

A common use case for wanting to calculate the frame a label will take up is for sizing table view cells appropriately. The recommended way of doing this is using the NSString method boundingRectWithSize:options:attributes:context:. options takes String drawing options: NSStringDrawingUsesLineFr...

iOS • UILabel

Use requestAnimationFrame to fade in element

View jsFiddle: https://jsfiddle.net/HimmatChahal/jb5trg67/ Copy + Pasteable code below: <html> <body> <h1>This will fade in at 60 frames per second (or as close to possible as your hardware allows)</h1> <script> // Fad...

JavaScript • requestAnimationFrame

Devise Controller Filters & Helpers

To set up a controller with user authentication using devise, add this before_action: (assuming your devise model is 'User'): before_action :authenticate_user! To verify if a user is signed in, use the following helper: user_signed_in? For the current signed-in user, use this helper: current_us...

Ruby on Rails • User Authentication in Rails

Simple lambda expressions

// A simple adder function defined as a lambda expression. // Unlike with regular functions, parameter types often may be omitted because the // compiler can infer their types let adder = |a, b| a + b; // Lambdas can span across multiple lines, like normal functions. let multiplier = |a: i32, ...

Rust • Closures and lambda expressions

select_related for all queries

Model with ForeignKey We will work with these models : from django.db import models class Book(models.Model): name= models.CharField(max_length=50) author = models.ForeignKey(Author) class Author(models.Model): name = models.CharField(max_length=50) Suppose we often (always) access ...

Django • Custom Managers and Querysets

Hello World

The program outputs Hello World! to standard output. module HELLO_WORLD(); // module doesn't have input or outputs initial begin $display("Hello World"); $finish; // stop the simulator end endmodule Module is a basic building block in Verilog. It represent a collection...

verilog • Hello World

belongs_to

A belongs_to association sets up a one-to-one connection with another model, so each instance of the declaring model "belongs to" one instance of the other model. For example, if your application includes users and posts, and each post can be assigned to exactly one user, you'd declare th...

Ruby on Rails • ActiveRecord Associations

Slicing with labels

When using labels, both the start and the stop are included in the results. import pandas as pd import numpy as np np.random.seed(5) df = pd.DataFrame(np.random.randint(100, size=(5, 5)), columns = list("ABCDE"), index = ["R" + str(i) for i in range(5)]) ...

pandas • Indexing and selecting data