Data Structures and Algorithms in Python

Appendix A

Character Strings in Python

A string is a sequence of characters that come from some alphabet. In Python, the built-in str class represents strings based upon the Unicode international character set, a 16-bit character encoding that covers most written languages. Unicode is an extension of the 7-bit ASCII character set that includes the basic Latin alphabet, numerals, and common symbols. Strings are particularly important in most programming applications, as text is often used for input and output.

A basic introduction to the str class was provided in Section 1.2.3, including use of string literals, such as 'hello', and the syntax str(obj) that is used to construct a string representation of a typical object. Common operators that are supported by strings, such as the use of + for concatenation, were further discussed in Section 1.3. This appendix serves as a more detailed reference, describing convenient behaviors that strings support for the processing of text. To organize our overview of the str class behaviors, we group them into the following broad categories of functionality.

Searching for Substrings

The operator syntax, pattern in s, can be used to determine if the given pattern occurs as a substring of string s. Table A.1 describes several related methods that determine the number of such occurrences, and the index at which the leftmost or rightmost such occurrence begins. Each of the functions in this table accepts two optional parameters, start and end, which ...