Tutorial by Examples: an

Generally speaking, empty commits (or commits with state that is identical to the parent) is an error. However, when testing build hooks, CI systems, and other systems that trigger off a commit, it's handy to be able to easily create commits without having to edit/touch a dummy file. The --allow-e...

Regular instances require: All instance types must be of the form (T a1 ... an) where a1 ... an are *distinct type variables*, and each type variable appears at most once in the instance head. That means that, for example, while you can create an instance for [a] you can't create an instance f...

This is a type system extension that allows types that are existentially quantified, or, in other words, have type variables that only get instantiated at runtime†. A value of existential type is similar to an abstract-base-class reference in OO languages: you don't know the exact type in contains,...

Database transactions ensure that a set of data changes will only be made permanent if every statement is successful. Any query or code failure during a transaction can be caught and you then have the option to roll back the attempted changes. PDO provides simple methods for beginning, committing,...

If a function contains just one expression, we can omit the brace brackets and use an equals instead, like a variable assignment. The result of the expression is returned automatically. fun sayMyName(name: String): String = "Your name is $name"

One of the very basic animations that you could come across is the NumberAnimation. This animation works by changing the numeric value of a property of an item from an initial state to a final state. Consider the following complete example: import QtQuick 2.7 import QtQuick.Controls 2.0 ...

iex(1)> 1 + 1 2 iex(2)> v 2 iex(3)> 1 + v 3 See also: Get the value of a row with `v`

Dim array = New Integer() {1, 2, 3, 4} or Dim array As Int32() = {1, 2, 3, 4}

A model can provide a lot more information than just the data about an object. Let's see an example and break it down into what it is useful for: from django.db import models from django.urls import reverse from django.utils.encoding import python_2_unicode_compatible @python_2_unicode_compati...

You can also combine several operators together to create more complex WHERE conditions. The following examples use the Employees table: Id FName LName PhoneNumber ManagerId DepartmentId Salary Hire_date CreatedDate ModifiedDate 1 James Smith 1234567890 NULL ...

ViewData is the mechanism for a controller to provide data to the view it presents, without using a ViewModel. Specifically, ViewData is a dictionary which is available both in MVC action methods and views. You may use ViewData to transfer some data from your action method to the view returned by th...

For instance, a computation involving commands to read and write from the prompt: First we describe the "commands" of our computation as a Functor data type {-# LANGUAGE DeriveFunctor #-} data TeletypeF next = PrintLine String next | ReadLine (String -> next) derivin...

There are two parts of a class: the interface and the implementation. The interface is the exposed functionality of the class. Its public methods and variables are part of the interface. The implementation is the internal workings of a class. Other classes shouldn't need to know about the implemen...

Empty array np.empty((2,3)) Note that in this case, the values in this array are not set. This way of creating an array is therefore only useful if the array is filled later in the code. From a list np.array([0,1,2,3]) # Out: array([0, 1, 2, 3]) Create a range np.arange(4) # Out: array(...

The basics After making changes to your source code, you should stage those changes with Git before you can commit them. For example, if you change README.md and program.py: git add README.md program.py This tells git that you want to add the files to the next commit you do. Then, commit your...

If an object is defined with static, thread, or automatic storage duration, and it has a character type, either: char, unsigned char, or signed char, it may not be accessed by a non-character type. In the below example a char array is reinterpreted as the type int, and the behavior is undefined on e...

First download anaconda from the Continuum site. Either via the graphical installer (Windows/OSX) or running a shell script (OSX/Linux). This includes pandas! If you don't want the 150 packages conveniently bundled in anaconda, you can install miniconda. Either via the graphical installer (Window...

Forms can be defined, in a similar manner to models, by subclassing django.forms.Form. Various field input options are available such as CharField, URLField, IntegerField, etc. Defining a simple contact form can be seen below: from django import forms class ContactForm(forms.Form): contac...

Channels can be used to send data from one thread to another. Below is an example of a simple producer-consumer system, where the main thread produces the values 0, 1, ..., 9, and the spawned thread prints them: use std::thread; use std::sync::mpsc::channel; fn main() { // Create a channel...

The notation 'thing is equal to (quote thing). The reader will do the expansion: > (read-from-string "'a") (QUOTE A) Quoting is used to prevent further evaluation. The quoted object evaluates to itself. > 'a A > (eval '+ 1 2) 3