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In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
A list may contain the same value more than once, and each occurrence is considered a distinct item. A singly-linked list structure, implementing a list with three integer elements. The term list is also used for several concrete data structures that can be used to implement abstract lists, especially linked lists and arrays.
In all versions of Python, boolean operators treat zero values or empty values such as "", 0, None, 0.0, [], and {} as false, while in general treating non-empty, non-zero values as true. The boolean values True and False were added to the language in Python 2.2.1 as constants (subclassed from 1 and 0 ) and were changed to be full blown ...
In Python, == compares by value. Python's is operator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example, a <= b <= c. Python uses and, or, and not as Boolean operators. Python has a type of expression named a list comprehension, and a more general expression named a generator ...
Download as PDF; Printable version; ... The MediaWiki parameter default function doesn't return the default value for empty parameters. ... in the above examples ...
Instead, any value can behave as Boolean in Boolean context (condition of if or while statement, argument of && or ||, etc.). The number 0, the strings "0" and "", the empty list (), and the special value undef evaluate to false. [8] All else evaluates to true. Lua has a Boolean data type, but non-Boolean values can also behave as Booleans.
An empty list (), which is a special object usually called nil. A cons cell whose car is the first element of the list and whose cdr is a list containing the rest of the elements. This forms the basis of a simple, singly linked list structure whose contents can be manipulated with cons , car , and cdr .
Every finite or countably infinite subset of the real numbers is a null set. For example, the set of natural numbers , the set of rational numbers and the set of algebraic numbers are all countably infinite and therefore are null sets when considered as subsets of the real numbers.