Tutorial by Examples: od

Example for reading file data_file.csv such as: File: index,header1,header2,header3 1,str_data,12,1.4 3,str_data,22,42.33 4,str_data,2,3.44 2,str_data,43,43.34 7, str_data, 25, 23.32 Code: pd.read_csv('data_file.csv') Output: index header1 header2 header3 0 1 str_dat...

Models are typically defined in the models.py file under your application subdirectory. The Model class of django.db.models module is a good starting class to extend your models from. For example: from django.db import models class Book(models.Model): title = models.CharField(max_length=100...

select LastName, FirstName, from Person Returns message: Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from Person' at line 2. Getting a "1064 error" message from MySQL mean...

// decode NSString *string = [[NSString alloc] initWithData:utf8Data encoding:NSUTF8StringEncoding]; // encode NSData *utf8Data = [string dataUsingEncoding:NSUTF8StringEncoding]; Some supported encodings are: NSASCIIStringEncoding NSUTF8StringEnc...

There are several ways methods can be inherited public abstract class Car { public void HonkHorn() { // Implementation of horn being honked } // virtual methods CAN be overridden in derived classes public virtual void ChangeGear() { // Implementation of gear...

A function defined as async is a function that can perform asynchronous actions but still look synchronous. The way it's done is using the await keyword to defer the function while it waits for a Promise to resolve or reject. Note: Async functions are a Stage 4 ("Finished") proposal on tr...

A context manager is an object that is notified when a context (a block of code) starts and ends. You commonly use one with the with statement. It takes care of the notifying. For example, file objects are context managers. When a context ends, the file object is closed automatically: open_file = ...

In Python 2, an iterator can be traversed by using a method called next on the iterator itself: Python 2.x2.3 g = (i for i in range(0, 3)) g.next() # Yields 0 g.next() # Yields 1 g.next() # Yields 2 In Python 3 the .next method has been renamed to .__next__, acknowledging its “magic” ro...

The null coalescing operator makes it easy to ensure that a method that may return null will fall back to a default value. Without the null coalescing operator: string name = GetName(); if (name == null) name = "Unknown!"; With the null coalescing operator: string name = GetN...

Suppose you have defined the following Person class: public class Person { String name; int age; public Person (int age, String name) { this.age = age; this.name = name; } } If you instantiate a new Person object: Person person = new Person(25, &qu...

CommandDescription<Esc>Leaves insert mode, triggers autocommands and abbreviations<C-[>Exact synonymous of <Esc><C-c>Leaves insert mode, doesn't trigger autocommands Some people like to use a relatively uncommon pair of characters like jk as shortcut for <Esc> or <C...

Download and install Visual Studio. Visual Studio can be downloaded from VisualStudio.com. The Community edition is suggested, first because it is free, and second because it involves all the general features and can be extended further. Open Visual Studio. Welcome. Go to File → New ...

Given a random vector v = rand(10,1); if you want the sum of its elements, do NOT use a loop s = 0; for ii = 1:10 s = s + v(ii); end but use the vectorized capability of the sum() function s = sum(v); Functions like sum(), mean(), prod() and others, have the ability to operate ...

Method overloading, also known as function overloading, is the ability of a class to have multiple methods with the same name, granted that they differ in either number or type of arguments. Compiler checks method signature for method overloading. Method signature consists of three things - Met...

Method overriding is the ability of subtypes to redefine (override) the behavior of their supertypes. In Java, this translates to subclasses overriding the methods defined in the super class. In Java, all non-primitive variables are actually references, which are akin to pointers to the location of...

Using reflection, a method of an object can be invoked during runtime. The example shows how to invoke the methods of a String object. import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; String s = "Hello World!"; // method without parameters // i...

Let's say we have an interface for logging: interface Logger { function log($message); } Now say we have two concrete implementations of the Logger interface: the FileLogger and the ConsoleLogger. class FileLogger implements Logger { public function log($message) { // Append...

SQLiteOpenHelper is a helper class to manage database creation and version management. In this class, the onUpgrade() method is responsible for upgrading the database when you make changes to the schema. It is called when the database file already exists, but its version is lower than the one spec...

Enums can define abstract methods, which each enum member is required to implement. enum Action { DODGE { public boolean execute(Player player) { return player.isAttacking(); } }, ATTACK { public boolean execute(Player player) { re...

Responding to Editing Notifications textViewShouldBeginEditing(_:) textViewDidBeginEditing(_:) textViewShouldEndEditing(_:) textViewDidEndEditing(_:) Responding to Text Changes textView(_:shouldChangeTextIn:replacementText:) textViewDidChange(_:) Responding to URL textView(_: UITe...