How do I refer to the null object in Python?

In Python, the 'null' object is the singleton None.

The best way to check things for "Noneness" is to use the identity operator, is:

if foo is None:
    ...

source - http://stackoverflow.com/questions/3289601/null-object-in-python

HTML DOM Events

HTML DOM Events

HTML DOM events allow JavaScript to register different event handlers on elements in an HTML document.

Events are normally used in combination with functions, and the function will not be executed before the event occurs (such as when a user clicks a button).

Tip: The event model was standardized by the W3C in DOM Level 2.

HTML DOM Events

DOM: Indicates in which DOM Level the property was introduced.

Mouse Events

Keyboard Events

Frame/Object Events

Form Events

Drag Events

Clipboard Events

Print Events

Media Events

Animation Events

Transition Events

Server-Sent Events

Misc Events

Touch Events

Event Object

Constants

Properties

Methods

MouseEvent Object

KeyboardEvent Object

HashChangeEvent Object

PageTransitionEvent Object

FocusEvent Object

AnimationEvent Object

TransitionEvent Object

WheelEvent Object

source - http://www.w3schools.com/jsref/dom_obj_event.asp

KeyboardEvent keyCode Property

 Event Object

More "Try it Yourself" examples below.

Definition and Usage

The keyCode property returns the Unicode character code of the key that triggered the onkeypress event, or the Unicode key code of the key that triggered theonkeydown or onkeyup event.

The difference between the two code types:

• Character codes - A number which represents an ASCII character
• Key codes - A number which represents an actual key on the keyboard

These types do not always mean the same thing; for example, a lower case "w" and an upper case "W" have the same keyboard code, because the key that is pressed on the keyboard is the same (just "W" = the number "87"), but a different character code because the resulting character is different (either "w" or "W", which is "119" or "87") - See "More Examples" below to better understand it.

Tip: To find out if the user is pressing a printable key (e.g. "a" or "5"), it is recommended to use this property on the onkeypress event. To find out if the user is pressing a function key (e.g. "F1", "CAPS LOCK" or "Home") use the onkeydown or onkeyup event.

Note: In Firefox, the keyCode property does not work on the onkeypress event (will only return 0). For a cross-browser solution, use the which property together with keyCode, e.g:

Tip: For a list of all Unicode characters, please study our Complete Unicode Reference.

Tip: If you want to convert the returned Unicode value into a character, use the fromCharCode() method.

Note: This property is read-only.

Note: Both the keyCode and which property is provided for compatibility only. The latest version of the DOM Events Specification recommend using the keyproperty instead (if available).

Tip: If you want to find out whether the "ALT", "CTRL", "META" or "SHIFT" key was pressed when a key event occured, use the altKey, ctrlKey, metaKey orshiftKey property.

source - http://www.w3schools.com/jsref/event_key_keycode.asp