Tutorial by Examples: g

With a through model

class Skill(models.Model): name = models.CharField(max_length=50) description = models.TextField() class Developer(models.Model): name = models.CharField(max_length=50) skills = models.ManyToManyField(Skill, through='DeveloperSkill') class DeveloperSkill(models.Model): ...

Django • Many-to-many relationships

Print out an Analog Value

int val = 0; // variable used to store the value // coming from the sensor void setup() { Serial.begin(9600); //Begin serializer to print out value // Note: Analogue pins are // automatically set as inputs } void loop() { val = analogRead(0); // read the va...

arduino • Analog Inputs

Do not catch everything!

While it's often tempting to catch every Exception: try: very_difficult_function() except Exception: # log / try to reconnect / exit gratiously finally: print "The END" # it runs no matter what execute. Or even everything (that includes BaseException and all its c...

Python Language • Exceptions

Catching multiple exceptions

There are a few ways to catch multiple exceptions. The first is by creating a tuple of the exception types you wish to catch and handle in the same manner. This example will cause the code to ignore KeyError and AttributeError exceptions. try: d = {} a = d[1] b = d.non_existing_fiel...

Python Language • Exceptions

Using Single-case Discriminated Unions as Records

Sometimes it is useful to create union types with only one case to implement record-like types: type Point = Point of float * float let point1 = Point(0.0, 3.0) let point2 = Point(-2.5, -4.0) These become very useful because they can be decomposed via pattern matching in the same way as tu...

F# • Discriminated Unions

Instantiating class with no parameter: {} vs ()

Let's say we have a class MyClass with no constructor argument: class MyClass In Scala we can instantiate it using below syntax: val obj = new MyClass() Or we can simply write: val obj = new MyClass But, if not paid attention, in some cases optional parenthesis may produce some unexpecte...

Scala Language • Classes and Objects

Singleton & Companion Objects

Singleton Objects Scala supports static members, but not in the same manner as Java. Scala provides an alternative to this called Singleton Objects. Singleton objects are similar to a normal class, except they can not be instantiated using the new keyword. Below is a sample singleton class: object...

Scala Language • Classes and Objects

Using map to reformat objects in an array

Array.prototype.map(): Returns a new array with the results of calling a provided function on every element in the original array. The following code example takes an array of persons and creates a new array containing persons with a 'fullName' property var personsArray = [ { id: 1, f...

JavaScript • Arrays

Passing arguments by reference or value

In JavaScript all arguments are passed by value. When a function assigns a new value to an argument variable, that change will not be visible to the caller: var obj = {a: 2}; function myfunc(arg){ arg = {a: 5}; // Note the assignment is to the parameter variable itself } myfunc(obj); conso...

JavaScript • Functions

Assert Error Messages

A trick exists that can display an error message along with an assertion. Normally, you would write code like this void f(void *p) { assert(p != NULL); /* more code */ } If the assertion failed, an error message would resemble Assertion failed: p != NULL, file main.c, line 5 Ho...

C Language • Assertion

Escaping curly brackets inside a String.Format() expression

string outsidetext = "I am outside of bracket"; string.Format("{{I am in brackets!}} {0}", outsidetext); //Outputs "{I am in brackets!} I am outside of bracket"

C# Language • String.Format

Distance Filter using

Example : CLLocationManager *locationManager = [[CLLocationManager alloc] init]; locationManager.delegate = self; locationManager.desiredAccuracy = kCLLocationAccuracyBest; locationManager.distanceFilter = 5; E.g. In the above example code above, location changes of less than 5 m...

iOS • CLLocation

Using ngStorage to share data

Firstly, include the ngStorage source in your index.html. An example injecting ngStorage src would be: <head> <title>Angular JS ngStorage</title> <script src = "http://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script> &l...

AngularJS • Sharing Data

Declaring permissions in your manifest file

Any permission required by your application to access a protected part of the API or to interact with other applications must be declared in your AndroidManifest.xml file. This is done using the <uses-permission /> tag. Syntax <uses-permission android:name="string" android...

Android • The Manifest File

Create Single Gift Card

// Instantiate Gift Card Model $gift_card = Mage::getModel('enterprise_giftcardaccount/giftcardaccount'); // Populate Gift Card values $gift_card // Your redeemable code, doesn't have to be in this format. ->setCode('2i2j2j-24k1ii1-67774k-231l') // Also has STATUS_DISABLED ...

magento • Create Enterprise Gift Cards Programmatically

Mistakenly writing = instead of == when comparing

The = operator is used for assignment. The == operator is used for comparison. One should be careful not to mix the two. Sometimes one mistakenly writes /* assign y to x */ if (x = y) { /* logic */ } when what was really wanted is: /* compare if x is equal to y */ if (x == y) { ...

C Language • Common pitfalls

Getting a shell into a running (detached) container

Log into a running container A user can enter a running container in a new interactive bash shell with exec command. Say a container is called jovial_morse then you can get an interactive, pseudo-TTY bash shell by running: docker exec -it jovial_morse bash Log into a running container with a s...

Docker • Running containers

Using an extension method for collection initialization

Collection initialization syntax can be used when instantiating any class which implements IEnumerable and has a method named Add which takes a single parameter. In previous versions, this Add method had to be an instance method on the class being initialized. In C#6, it can also be an extension me...

C# Language • C# 6.0 Features

Context switching

The two possible ways of issuing a context.become (replacing or adding the new behavior) are offered separately to enable a clutter-free notation of nested receives: val a = actor(new Act { become { // this will replace the initial (empty) behavior case "info" ⇒ sender() ! "A...

akka • Actor DSL

Life-cycle Management

Life-cycle hooks are also exposed as DSL elements, where later invocations of the methods shown below will replace the contents of the respective hooks: val a = actor(new Act { whenStarting { testActor ! "started" } whenStopping { testActor ! "stopped" } }) The above i...

akka • Actor DSL