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A string is a substring (or factor) [1] of a string if there exists two strings and such that =.In particular, the empty string is a substring of every string. Example: The string = ana is equal to substrings (and subsequences) of = banana at two different offsets:
The empty string has several properties: |ε| = 0. Its string length is zero. ε ⋅ s = s ⋅ ε = s. The empty string is the identity element of the concatenation operation. The set of all strings forms a free monoid with respect to ⋅ and ε. ε R = ε. Reversal of the empty string produces the empty string, so the empty string is a palindrome.
String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly.
Python uses the + operator for string concatenation. Python uses the * operator for duplicating a string a specified number of times. The @ infix operator is intended to be used by libraries such as NumPy for matrix multiplication. [104] [105] The syntax :=, called the "walrus operator", was introduced in Python 3.8. It assigns values to ...
Example of Kleene star applied to the empty set: ∅ * = {ε}. Example of Kleene plus applied to the empty set: ∅ + = ∅ ∅ * = { } = ∅, where concatenation is an associative and noncommutative product. Example of Kleene plus and Kleene star applied to the singleton set containing the empty string:
Use of the word "string" to mean any items arranged in a line, series or succession dates back centuries. [5] [6] In 19th-century typesetting, compositors used the term "string" to denote a length of type printed on paper; the string would be measured to determine the compositor's pay. [7] [4] [8]
[7] [8] A detailed survey of indexing techniques that allows one to find an arbitrary substring in a text is given by Navarro et al. [7] A computational survey of dictionary methods (i.e., methods that permit finding all dictionary words that approximately match a search pattern) is given by Boytsov.
For example, a space character (U+0020 SPACE, ASCII 32) represents blank space such as a word divider in a Western script. A printable character results in output when rendered, but a whitespace character does not. Instead, whitespace characters define the layout of text to a limited degree, interrupting the normal sequence of rendering ...