Python in a Nutshell, 2nd Edition

Sequence Operations

Python supports a variety of operations applicable to all sequences, including strings, lists, and tuples. Some sequence operations apply to all containers (including, for example, sets and dictionaries, which are not sequences), and some apply to all iterables (meaning “any object on which you can loop,” as covered in Iterables; all containers, be they sequences or otherwise, are iterable, and so are many objects that are not containers, such as files, covered in File Objects, and generators, covered in Generators). In the following, I use the terms sequence, container, and iterable, quite precisely and specifically, to indicate exactly which operations apply to each category.

Sequences in General

Sequences are containers with items that are accessible by indexing or slicing. The built-in len function takes any container as an argument and returns the number of items in the container. The built-in min and max functions take one argument, a nonempty iterable whose items are comparable, and return the smallest and largest items, respectively. You can also call min and max with multiple arguments, in which case they return the smallest and largest arguments, respectively. The built-in sum function takes one argument, an iterable whose items are numbers, and returns the sum of the numbers.

Sequence conversions

There is no implicit conversion between different sequence types, except that plain strings are converted to Unicode strings if needed. (String conversion is ...